EVALUATION OF BORDER CROPS AND VARIETAL RESISTANCE FOR THE

MANAGEMENT OF DIAMONDBACK MOTH ( Plutella xylostella L.) ON CABBAGE

(Brassica oleracea var. capitata)

EDDIE BIRNIE S. HASHEELA

B.Sc. Agric (Crop Science) University of Namibia

A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQ UIREMENTS FOR

THE AWARD OF MASTER OF SCIENCE IN CROP PROTECTION

2009

ii

DECLARATION

I declare that this is an original version of my studies and has not been presented for an award of

a degree in any other University.

Signature……………………………………………………..Date………………………………

Eddie Birnie S. Hasheela

This thesis is submitted for examination with our approval as the University supervisors:

Signature……………………………… Date………………………….

Prof. J. H. Nderitu

Department of Plant Science and Crop Protection

Faculty of Agriculture, University of Nairobi

Signature……………………………. Date………………………….

Dr. F. M. Olubayo

Department of Plant Science and Crop Protection

Faculty of Agriculture, University of Nairobi

iii

DEDICATION

To my parents, brothers, sister and the entire Hasheela family for their supports and

encouragement

iv

ACKNOWLEDGEMENTS

I appreciate our Lord for giving me courage to undertake this study, and acknowledge the

Ministry of Agriculture, Water and Forestry of the Republic of Namibia for granting me the

scholarship and study leave. I am thankful to my supervisors Prof. J. H. Nderitu and Dr. F. M.

Olubayo for their guidance throughout the course of this work. I acknowledge the technical

assistance offered me by the technical staff, Department of Plant Science and Crop Protection,

and Kabete Field station. My regards also go to Dr. J. M. Kasina of National Agricultural

Research Laboratories (KARI - NARL) for his invaluable comments and tirelessly availing

himself for consultations and Mr. E. G. Thuranira (KARI-NARL) for assistance in statistical

inferences. Special tributes go to Mr. Godfrey Livasia who assisted me very much in the setting

up of field experiments. I also express my gratitude to the University of Nairobi management

particularly College of Agriculture and Veterinary Sciences, for granting me opportunity to study

at this University. Finally, my sincere appreciation goes to my family and relatives for their

unremitting support and concerns while undertaking my studies in Kenya.

v

TABLE OF CONTENTS Title page ………………………………………………………………………………………….i

Declaration ...................................................................................................................................... ii

Dedication ...................................................................................................................................... iii

Acknowledgement ......................................................................................................................... iv

Table of contents ............................................................................................................................. v

List of tables ................................................................................................................................. viii

List of plates ................................................................................................................................... ix

List of figures ................................................................................................................................. ix

Abstracts ......................................................................................................................................... x

CHAPTER 1: INTRODUCTION ................................................................................................ 1

1.1. Background Information .......................................................................................................... 1

1.2. Problem statement .................................................................................................................... 3

1.3. Justification .............................................................................................................................. 4

1.4. Objectives ................................................................................................................................ 5

1.5. Hypotheses ............................................................................................................................... 5

1.6. References ................................................................................................................................ 6

CHAPTER 2: LITERATURE REVIEW .................................................................................. 8

2.1. Cabbage Classification and Production ................................................................................... 8

2.2. Constraints to Cabbage production .......................................................................................... 8

2.3. Diamond back moth (DBM), Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) ......... 9

2.3.1. Pest status and Distribution of Diamondback moth .............................................................. 9

2.3.2. Biology and life cycle of Diamondback moth ...................................................................... 9

2.3.3. Host Plants of Diamondback moth .................................................................................... 11

vi

2.3.4. Symptoms of attacks on cabbage and related losses ........................................................... 12

2.3.5. Pest population .................................................................................................................... 13

2.4. Control of Diamondback moth .............................................................................................. 13

2.4.1. Biological control................................................................................................................ 13

2.4.2. Chemical ............................................................................................................................. 14

2.4.3. Cultural control ................................................................................................................... 15

2.4.3.1. Crop rotation or maintenance of a host-free season ......................................................... 15

2.4.3.2. Trap cropping ................................................................................................................... 16

2.4.3.3. Border trap cropping ........................................................................................................ 16

2.4.3.4. Row intercropping ........................................................................................................... 17

2.4.3.5. Companion cropping ........................................................................................................ 17

2.4.4. Host plant resistance ........................................................................................................... 18

2.5. References .............................................................................................................................. 19

CHAPTER 3: EVALUATION OF CABBAGE VARIETIES FOR RESI STANCE TO

DIAMONDBACK MOTH (Plutella xylostella) INFESTATION ................... 25

3.1. Abstract .................................................................................................................................. 25

3.2. Introduction ............................................................................................................................ 26

3.3. Material and methods ............................................................................................................. 27

3.4. Results .................................................................................................................................... 28

3.4.1. Immature Diamondback moth Infestation and fluctuation trends ...................................... 28

3.4.2. Diamondback moth damage levels ..................................................................................... 30

3.4.3. Yield .................................................................................................................................... 31

3.4. Discussion .............................................................................................................................. 33

3.5. References .............................................................................................................................. 35

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CHAPTER 4: EVALUATION OF BORDER CROPS ON THE DIAMON DBACK MOTH

(Plutellaxylostella) INFESTATION AND THE DAMAGE ON CABBAGE

(Brassica oleracea var. capitata) ……………………………….……...……….37

4.1. Abstract .................................................................................................................................. 37

4.2. Introduction ............................................................................................................................ 38

4.3. Material and Methods ............................................................................................................ 39

4.4. Results .................................................................................................................................... 40

4.4.1. Diamondback moth infestation and fluctuation trends ....................................................... 40

4.4.2. Diamondback moth damage levels ..................................................................................... 42

4.4.3. Yield .................................................................................................................................... 43

4.5. Discussion .............................................................................................................................. 45

4.6. References .............................................................................................................................. 46

CHAPTER 5: GENERAL DISCUSION, CONCLUSIONS AND

RECOMMENDATIONS .................................................................................. 49

5.1. General Discussion ................................................................................................................ 49

5.2. Conclusions ............................................................................................................................ 50

5.3. Recommendations .................................................................................................................. 51

5.3. References .............................................................................................................................. 52

viii

LIST OF TABLES Table 3.1. Cabbage damage Scores scale used at Kabete Field Station in 2008 and 2009

plantings ....................................................................................................................... 28

Table 3.2. Mean number of immature Diamondback moth on sprayed and unsprayed cabbage

varieties at Kabete Field Station. ................................................................................. 30

Table 3.3. Mean damage scores by Diamondback moth on cabbage varieties at Kabete

Field Station . .............................................................................................................. 31

Table 3.4. Mean number of marketable and unmarketable cabbage heads per variety at Kabete

Field Station. ................................................................................................................ 32

Table 3.5. Mean yield of marketable cabbage heads (Kg) at Kabete Field Station. .................... 32

Table 3.6. Relationship between immature Diamondback moth and damage scores on cabbage

heads at Kabete Field Station. ........................................................................................ 33

Table 4.1. Mean number of immature Diamondback moth on Cabbages surrounded by different

border crops at Kabete Field Station. ............................................................................ 42

Table 4.2. Mean damage scores on Cabbage surrounded by different border crops at Kabete

Field Station. ............................................................................................................... 43

Table 4.3. Mean number of marketable and unmarketable cabbage heads at Kabete

Field Station. ................................................................................................................ 44

Table 4.4. Mean weights (Kg) of marketable and unmarketable cabbage heads from plots

surrounded with different border crops at Kabete Field Station. ................................. 44

Table 4.4. Relationship between immature Diamondback moth and damage scores on cabbage

heads at Kabete Field Station. ..................................................................................... 45

ix

LIST OF PLATES

Plate 1: Cabbage damaged by Diamondback moth ...................................................................... 13

LIST OF FIGURES

Figure 3.1. Mean number of immature Diamondback moth on sprayed and unsprayed cabbage

varieties at Kabete Field Station. ................................................................................... 29

Figure 4.1. Mean number of immature Diamondback moth on Cabbage plots surrounded by

different border crops at Kabete Field Station. ............................................................... 41

x

ABSTRACT Cabbage (Brassica oleracea L. var. capitata) is one of the most important vegetables grown in

Kenya for home consumption and as an important source of income to many small-scale farmers.

The production of cabbage is, however, constrained by several pests. Among those pests,

Diamondback moth (Plutella xylostella) is ranked as the most important pest and is regarded as

the most destructive insect pest of cruciferous crops worldwide. As an attempt to overcome the

problem, field experiments were conducted at the University of Nairobi, College of Agriculture

and Veterinary Sciences farm in 2008 and 2009. The study was carried out to screen six cabbage

varieties for resistance and evaluate the effects of border crops on Diamondback moth infestation

and damage on cabbage. Six cabbage varieties which were screened were: Drumhead, Sugarloaf,

Golden Acre, Gloria F1, Copenhagen Market and Pruktor F1. The experiment was set up in a

split plot design consisting of four replicates per treatment whereby one set of the treatments

were sprayed with Dimethoate and the others were not sprayed. The cabbage varieties were

compared in Diamondback moth damage and infestation. In border crops experiment, crops

evaluated were Indian mustard, Radish, Kale, Tomato, Coriander and Cleome. They were

planted around cabbage Copenhagen Market variety in the field 15 days prior to cabbage

transplanting. The experiment was laid out using a Randomised Complete Block Design (RCBD)

consisting of four replicates. In both experiments, five randomly selected plants per plot were

used to record the numbers of larvae, pupae and damage scores. The yield in terms of quality and

quantity of cabbage heads per variety were assessed on all the plants per plot at maturity stage. It

was evident from the study that there were significant differences (P<0.05) among the sprayed

and unsprayed varieties on infestation by the immature DBM. Among the sprayed and unsprayed

treatments, Copenhagen Market and Pruktor F1 had the lowest mean number of the immature

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Diamondback moth. The unsprayed varieties recorded higher DBM damage compared with the

sprayed varieties. The lowest damage was recorded on cabbage var. Pruktor F1 and Sugarloaf

both in sprayed and unsprayed treatments. Among the unsprayed varieties, cabbage var. Pruktor

F1 and Copenhagen Market had the highest number of the marketable cabbage heads. However,

the highest cabbage head weights were recorded from Pruktor F1 in the sprayed as well as in the

unsprayed treatments. The study on border crops indicated that the mean number of immature

Diamondback moth was significantly lower (P<0.05) on cabbages surrounded by the Indian

mustard and Coriander border crops compared with those surrounded by the other crops. The

results also indicated that cabbage plots bordered with the Indian mustard had the lowest number

of damaged cabbage heads. Plots surrounded with Indian mustard and Coriander border crops

produced highest marketable cabbage heads and highest cabbage head weights. The results

obtained in these studies reveal that cabbage var. Pruktor F1 and Copenhagen market and Indian

mustard border crop can be adopted by farmers for the management of Diamondback moth on

cabbage.

1

CHAPTER 1 INTRODUCTION

1.1. Background information

Cabbage (Brassica oleracea var. capitata L.) is one of the most important vegetables grown in

Kenya. It is grown in all the eight provinces of Kenya, but mostly at altitudes of 800-2000 m

above sea level. The major growing provinces are Central and Rift Valley provinces with 40%

and 39% respectively of the total national production. In Kenya, the cabbage average annual

production from 2002 to 2005 was 416,373.0 tons (MOA, 2006). Commercially, the world

annual average production in 2005 was about 62 million metric tons of the fresh heads from 2.8

million hectares (FAO, 2007).

Cabbage is grown under both rain fed and irrigated conditions by both small and medium scale

farmers and marketed in rural and urban areas. In the local farming systems, cabbage is usually

part of a diversified cropping pattern, and is mostly grown as a cash crop for local market

(Macharia et al., 2005). It is used as an important source of vitamins, is relatively high in

vitamins A and C but it is low in protein content, and minerals particularly potassium as well as

source of income for smallholder farmers. Other cultivars like the green cabbages tend to be

higher in vitamin A than the red cabbages, while savoy types tend to have more vitamin A than

the smooth types (Bewick, 1994).

Cabbage production is hindered by many insect pests and diseases. Insect pests like

Diamondback moth (DBM), cabbage looper and cabbage-worm comprise the major insect pests

attacking this crop. Therefore, in order to produce blemish-free cabbage heads so as to meet the

market and consumer demands, growers rely on routine chemical insecticide applications. Such

2

kind of widespread and intensive use of insecticides and the genetic elasticity of DBM have led

to serious problems including insecticide resistance which have prompted the need of alternative

control methods (Vickers et al., 2004; Sarfraz and Keddie, 2005). Incidences of resistance to

insecticides in DBM occurs every where even whenever different classes of insecticides are used

for control (Talekar and Shelton, 1993). Also, routine spraying has a disastrous impact on the

natural populations of beneficial insects in a cabbage field. Additionally, routine spray

applications are costly, have negative impacts on the environment, human health, non targets and

the overall farm ecosystem.

Diamondback moth has become the most abundant and damaging pest of cruciferous crops in

Kenya and has gained economic importance over the years. Integrated Pest Management (IPM)

systems based on functional biodiversity and ecological engineering have been considered to be

the only viable long-term solutions to combat this pest (Verkerk and Wright, 1996). The ability

of DBM to develop resistance to nearly all the available insecticides, combined with concerns

about the impact of excessive insecticide use on human health and the environment, have

stimulated interest in the alternative management practices such as trap cropping. Several types

of trap crops have been recommended for DBM management, including collards (Brassica

oleracea var. acephala) and Indian mustard (Brassica juncea L.) (Shelton et al., 2007).

However, the results have been variable because populations of DBM often develop on these

trap crops and spill over to the cash crop. The control measures adopted as part of an IPM

package is based on many factors some of which include available resources, such as money,

manpower, technical knowhow, skills; the agroecosystem; geographical location and socio-

economic situations. Host plant resistance forms an important component of the integrated pest

3

management programs. Resistant cultivars cost the farmer little, nor does their adoption

necessarily disrupt his farming system.

1.2. Problem statement

Diamondback moth is one of the most important and destructive pests on crucifers worldwide.

Particularly in Kenya, Diamondback moth population cause heavy damage to brassicas in

different districts of the country (Rossbach et al., 2006). Brassica producers are experiencing

serious economic losses caused by Diamondback moth despite the effort mostly by small scale

farmers on control measures by mostly using new insecticides of different classes. The pest is

known to cause damage amounting to 90% loss of the cabbage yield (Verkerk and Wright, 1996)

and it is estimated to cause losses amount to US$7.9 million per year in the whole country

(Macharia et al., 2005). As an attempt to reduce crop losses, farmers tend to use insecticides

repeatedly but this does not alleviate the problem since Diamondback moth has potential

capacity to develop resistance to insecticides (Safraz et al., 2005). However, the destructiveness

of DBM has made this pest the focus of Integrated Pest Management research because it is only

the multiple-component of the Integrated Pest Management strategies can offer the greatest

opportunities for the acceptable management of this insect. The use of cultural measures in

Integrated Pest Management cannot be over emphasized with exclusion of integrating cultural

control measures (Momanyi et al., 2006). Therefore, Diamondback moth needs to be managed in

a more sustainable manner that should include the development of multiple management

practices such as the non-chemical techniques. This study was conducted to evaluate the

potential of border crops and resistant varieties in reducing infestation and damage of cabbage by

Diamondback moth.

4

1.3. Justification

Several reports in Kenya have indicated that there is serious DBM damage on cabbage even

when pesticides are used to control the pest (Odour et al., 1996). Diamondback moth is known to

have a potential capacity to develop resistance to pesticides in a short period of time. Conversely,

pesticides can affect negatively even beneficial insects, such as natural enemies, and cause even

contamination on the produce. This problem has prompted the need for more rational approach,

namely Intergraded Pest Management (IPM), to seek for control methods which are able to

maximize the use of safer and effective alternatives. There is urgent need to reduce the use of

pesticides in the management of Diamondback moth by making use of other pest control

methods which can allow little use of pesticides. Such pest management methods can be

developed through conducting research to generate more knowledge about their potential. These

include cultural methods such as use of insect-resistant varieties, trap and companion cropping

systems. Cultural control methods depend on adequate knowledge of the pest’s life history, host

plant interactions and other aspects of its biology. Plants used in trap and companion cropping

systems repel or attract insect pests thus lowering the pest’s general equilibrium position. This

enables the farmer to spray only on trap or companion crops whenever the particular insect pest

population reaches economic threshold level in plants without contaminating the main crop. One

positive impact of such control measure will be spending less on pesticides which are even too

expensive for most small scale farmers unless provided with subsidy by the government. This

study seeks to evaluate the potential usage of different trap crops, through use of attractive and

repulsive plants, and to evaluate different cabbage varieties for resistance to DBM infestation in

cabbage as an environmental friendly approach.

5

1.4. Objectives 1.4.1. Overall objective

To evaluate the potential of trap crops and cabbage varieties in reducing infestation and damage

of caused by Diamondback moth.

1.4.2. Specific objectives:

1. To evaluate cabbage varieties for resistance to Diamondback moth infestation.

2. To evaluate the effect of border crops on Diamondback moth infestation and damage on

cabbage.

1.5. Hypotheses 1. Diamondback moth infestation and damage on cabbage do not differ significantly with

use of different border crops

2. All cabbage varieties are infested similarly by Diamondback moth

6

1.6. References

Bewick, T.A. (1994). Cabbage: Use and production. University of Florida: Florida Cooperate

Extension Service Fact Sheet H5-712.

FAO (2007). FAO database. http://www.fao.org.

Macharia, I., Löhr, B. and De Groote, H. (2005). Assessing the potential impact of

biological control of Plutella xylostella (Diamondback moth) in cabbage production in

Kenya. Crop Protection. 24: 981 – 989.

MOA (2006). Ministry of Agriculture, Kenya: Annual Report of year 2005, Nairobi-Kenya.

Momanyi, C. M, Lohr, B. and Gitonga, L. (2006). Biological impact of the exotic parasitoid,

Diadegma semiclausum (Hellen), of Diamondback moth, Plutella xylostella L., in

Kenya. Biological Control 38: 254-263.

Odour, G. I., Löhr, B., Seif, A. A. (1996). Seasonality of major cabbage pests and incidence of

their enemies in Central of Kenya. In: Sirvapragragasam, Lim (Eds.), The

Management of DBM and Other Crucifer Pests. Proceeding of the Third International

Workshop, Kuala Lumpur, Malaysia.

Rossbach, A., B. Löhr, B and Vidal, S. (2006). Host shift to peas in the Diamondback moth

Plutella xylostella (Lepidoptera: Plutellidae) and response of its parasitoid Diadegma

mollipla (Hymenoptera: Ichneumonidae) Bulletin of Entomological Research 96, 413–

419.

Sarfraz, M. and Keddie, B. A. (2005). Conserving the efficacy of insecticides against Plutella

xylostella (L.) (Lep., Plutellidae). Journal Applied Entomology 129: 149–157.

7

Shelton, A.M., Hatch, S.L., Zhao, J.Z., Chen, M., Earle, E.D. and Cao, J. (2007). Suppression of

Diamondback moth using Bt-transgenic plants as a trap crop. Crop Protection. 27: (3-

5), 403-409.

Talekar, N. S. and Shelton, A. M. (1993). Biology, ecology, and management of the

Diamondback moth. Annual Review of Entomology 38: 275–301.

Verkerk, R. H. J. and Wright, D. J. (1996). Common cabbage resistance mechanisms against the

Diamondback moth: Annal of Applied Biology 128: 571–577.

Vickers, R. A., Furlong, M. J., White, A. and Pell, J. K. (2004). Initiation of fungal epizootics in

Diamondback moth populations within a large field cage: proof of concept of auto

dissemination. Entomologia Experimentalis et Applicata 111: 7–17.

8

CHAPTER 2

LITERATURE REVIEW

2.1. Cabbage classification and production

Cabbage belongs to Brassicaceae (or Cruciferae) family and is one of the plants that belong to

the Capitata group. The original Brassica oleracea ancestors originated from Mediterranean

region of Europe. Cabbage is classified as herbaceous, biennial, and a dicotyledonous flowering

plant with leaves forming a characteristic compact cluster (Nonnecke, 1989). During the first

half of the growing period, cabbage develops slowly for both early maturing and late maturing

varieties. In areas with high annual rainfall, sandy or sandy loam soils are described to be the

best because of their improved drainage. Cabbage requires high application of fertilizers and is

moderately sensitive to soil salinity (Lockhart and Wiseman, 1984).

2.2. Constraints to cabbage production

Major constraints of cabbage production in Kenya, like in other tropical countries, are pests and

diseases. Among cabbage diseases, the one taken to be most serious in constraining production

are Black rot (Xanthomonas campestris pv. campestris), Black leg (Phoma lingam) and Soft rot

caused by several different pathogens such as Erwinia carotovora pv. carotovora, Erwinia

chrysanthemi and Pseudomonas fluorescens (MOA, 2006). Cabbage insects pests include the

Diamondback moth (P. xylostella), and three species of aphids: Brevicoryne brassicae (L.),

Lipaphis erysimi (Kaltenbach), and Myzus persicae (Sulzer) (Odour et al., 1996). The

Diamondback moth is considered as the most destructive pest worldwide and occurs wherever

Brassica crops are cultivated (Talekar and Shelton, 1993). Its damage to cabbage crop results in

crop losses and low marketability due to contamination of the heads with larvae or their frass. In

9

order minimize output losses, farmers widely use synthetic pesticides and most farmers in Africa

solely depend on their use (Varela et al., 2003).

2.3. Diamond back moth (DBM), Plutella xylostella (Linnaeus) (Lepidoptera:

Plutellidae)

2.3.1. Pest status and distribution of diamondback moth

The Diamondback moth Plutella xylostella L. (Lepidoptera: Plutellidae), also referred to as

cabbage moth or Plutella, is believed to have originated from Mediterranean area but now is

found throughout the Americas and in Europe, Southeast Asia, Australia, Africa and New

Zealand (Hartcourt, 1955). Diamondback moth is a destructive insect pest of cruciferous crops

with a completely cosmopolitan distribution and can tolerate tropical, subtropical and temperate

climates (Sarfraz, et al., 2005). It is considered a major pest in all countries of Eastern and

Southern Africa region and is one of the most important pests of cruciferous plants throughout

the world. It is considered the most damaging insect pest of cruciferous crops throughout the

world (Talekar, 1992).

2.3.2. Biology and life cycle of diamondback moth

Normally Diamondback moth takes about 32 days to develop from egg to adult. However, time

to complete a generation may vary from 21 days to 32 days depending on weather and food

conditions. During its life cycle, several generations per growing season usually overlap and all

the four life stages may be present in the field at the same time (Oke, 2008).

Egg

Diamondback moth eggs are oval and flattened, and measure 0.44 mm long and 0.26 mm wide.

Eggs are yellow or pale green in color, and are deposited singly or in small groups of two to

10

eight eggs in depressions on the surface of foliage, or occasionally on other plant parts. Females

may deposit 250 to 300 eggs but the average total egg production is probably 150 eggs

(Capinera, 2000).The incubation period is 3 to 8 days depending on the environment (Varela et

al., 2003).

Larva

The Diamondback moth has four larval instars. Throughout their development, larvae remain

quite small and active. If disturbed, they often wriggle violently, move backward, and spin down

from the plant on a strand of silk. Overall length of each instar rarely exceeds 1.7, 3.5, 7.0, and

11.2 mm, respectively, for instars 1 through 4. Mean head capsule widths for these instars are

about 0.16, 0.25, 0.37, and 0.61 mm respectively. The larval body form tapers at both ends, and a

pair of prolegs protrudes from the posterior end, forming a distinctive "V" shape. The first instar

larvae are colorless but thereafter are pale green, and widest in the middle part of the body and

measure from 8 to12 mm when fully grown. The body bears relatively few hairs, which are short

in length, and most of them are marked by the presence of small white patches. Initially, the

feeding habit of the first instar larvae is leaf mining, although they are so small that the mines are

difficult to notice. The larvae emerge from their mines at the conclusion of the first instar, molt

beneath the leaf, and thereafter feed on the lower surface of the leaf. Their chewing results in

irregular patches of damage, and the upper leaf epidermis is often left intact. The total larval

period varies from 14 – 28 days and there are four larval instars (Varela et al., 2003).

Pupa

Harcourt (1955) reported that pupation occurs in a loose silk cocoon, usually formed on the

lower or outer leaves. In cauliflower and broccoli, pupation may occur in the florets. The

11

yellowish pupa is 7 to 9 mm in length. The pupa is greenish at first and changes to brown colour

as the moth develops. The duration of the cocoon averages about 8.5 days (range five to 15

days).

Adult

Diamondback moth is a small moth with long antennae. It is grayish-brown with a broad cream

or light brown band along the back. It has a characteristic diamond pattern on its back, which can

be seen when its wings are closed at rest (Varela et al., 2003). In females, the upper two-thirds of

forewing is light ochreous or light grey-ochreous, the contrast not so pronounced between upper

and lower portions in coloration, but the markings are like those of males. Adult males and

females live about 12 and 16 days, respectively, and females deposit eggs for about 10 days. The

moths are weak fliers, usually flying within 2 m of the ground, and not flying long distances.

However, they are readily carried by the wind. The adult is the overwintering stage in temperate

areas, but moths do not survive cold winters such as is found in most of Canada. They routinely

re-invade these areas each spring, evidently aided by southerly winds (Harcourt, 1955).

2.3.3. Host Plants

Throughout the world Diamondback moth is considered the main insect pest of crucifers,

particularly cabbages, broccoli and cauliflowers (Talekar and Shelton, 1993). Apart from crucifer

family, Talekar et al. (1993) reported that sporadic occurrences on other crops exist. For

example, Rossbach et al. (2006) reported population of Diamondback moth to shift to sugar

snap- and snow peas (Pisum sativum) in Kenya, resulting in heavy damage of those crops.

DBM attacks all cruciferous vegetable crops such as broccoli, brussels sprouts, cabbage, Chinese

cabbage, cauliflower, collard, kale, kohlrabi, mustard, radish, turnip, and watercress. The host

12

range is limited to crucifers because they contain mustard oils and their glucosides (Hillyer and

Thorsteinson, 1971). Many glucosites stimulate feeding in P. xylostella but two of these 3-

butenyl and 2-phenyl ethyl, are toxic at high concentrations (Nayar and Thorsteinson, 1963). Not

all crucifers are equally preferred for feeding and oviposition; however, collard green will

usually be chosen by the ovipositing moths relative to cabbage. Non-host plants may contain

these stimulants but also contain feeding inhibitors or toxins (Gupta and Thorsteinson, 1960).

Several cruciferous weeds are reported as important hosts, especially early in the season before

the cultivated crops are available (Valentine, 1998).

2.3.4. Symptoms of attacks on cabbage and related losses

The damage on cabbage is usually caused by newly hatched DBM caterpillars through feeding

inside the leaf tissue while older caterpillars normally feed on the entire leaf (Plate 1). After they

feed on the leaf tissues, the upper leaf surface remains intact characterized by a type of damage

called “windowing”. The damaged layer i.e. epidermis tear as the leaf grows, creating holes and

tear in the leaf. If caterpillars feed on the growing tips of the plant they disrupt head formation in

cabbage, broccoli, and cauliflower resulting in poor further normal development thus resulting to

deformation on the plant (Shelton et al., 1995). Although larvae are very small, their feeding can

cause complete removal of foliar tissue leaving the leaf veins only untouched. Sometimes large

caterpillars or cocoons hide in the heads which cause produce to be rejected for export, even if

the level of plant tissue removed is insignificant (Serafinchon, 2001). However, heavy damage

results in the marketable parts contaminated with excrement, which results to reduction in quality

and market values.

13

Plate 1: Cabbage damaged by Diamondback moth 2.3.5. Pest population

Diamondback moth life cycle can be completed in one to two weeks depending on the

temperature. Cool windy weather reduces adult activity and females often die before they lay all

their eggs. Heavy rainfall can reduce pest population by drowning small larvae. In the tropics,

the life cycle is shorter in the lowlands than in high altitudes which allow fast building of pest

population. Shelton et al. (1995) reported that DBM is a serious pest in the dry season, but during

heavy rains, large proportions of young larvae are often killed by rainfall. However, the most

important factor determining population trends is thought to be adult mortality.

2.4. Control of Diamondback moth

2.4.1. Biological control

In Kenya natural enemies such as larval endoparasitoid Diadegma semicclausum (Hellen) have

been evaluated as part of biological control of Diamondback moth to reduce dependence on the

use of synthetic pesticides (Momanyi et al., 2006). The parasitoid was introduced from Taiwana

for the control of Diamondback moth and was released in Nyamira District in Western Kenya for

the first time in July 2002. The released parasitoids were assessed after 27 months through data

14

collections made at equidistant points in four cardinal directions. It was indicated that the total

percentage parasitism increased from 12.7% recorded during the ten months baseline data

collection to 58.2% within the release area with D. semiclausum accounting for 94.7% of the

overall parasitism. The DBM population was low (below 1.0/plant) at all sampling points and

differences between the points of release were insignificant (Löhr et al., 2006). Other biological

control method reported in Kenya is the use of entomopathogenic nematodes which showed

great potential in the control of DBM (Nyasani et al., 2008). Similarly, the use of biological

agent’s isolates of the entomopathogenic fungi Beauveria bassiana Bba5653 isolates against

Diamondback moth larvae was reported to cause significant mortality of larvae compared with

other isolates (Godonou et al., 2008).

2.4.2. Chemical

Syed (1992) reported that pesticides have dominated attempts to control Plutella xylostella (L.)

for over 40 years. Controlling DBM with insecticides has become difficult and even

uneconomical due to resistance build up especially in the sub-tropical and tropical countries,

where farmers tend to grow cabbage continuously and applying mixture of chemical insecticides

sometimes more than twice a week (Sarfraz and Keddie, 2005). Such resistance development by

DBM is influenced by high fecundity, reproductive potential, a long growing season, extensive

acreage of crucifers and frequent insecticide applications (Magaro and Edelson, 1990). Most of

synthetic insecticides are not selective for the pest to be controlled and to some extent also affect

other living organisms especially parasites or predators of the pest against which treatment is

aimed.

15

2.4.3. Cultural control

Because of the failure of insecticides to control Diamondback moth, there is increased interest in

cultural control in commercial crucifer production. Various cultural control methods have been

used for Diamondback moth and these include intercropping, rotation and clean cultivation.

Endersby and Morgan (1991) provided a thorough review of cultural control methods against

Plutella xylostella, including physical barriers, physical toxicants, intercropping and companion

planting. Crop diversity can influence abundance of Diamondback moth. Larvae generally are

fewer in numbers and more heavily parasitized when crucifer crops are interplanted with another

crop or when weeds are present. Surrounding cabbage crops with two or more rows of more

preferred hosts such as collard and mustard can delay or prevent the dispersal of Diamondback

moth into cabbage crops (McHugh and Foster, 1995).

2.4.3.1. Crop rotation or maintenance of a host-free season

Crop rotation has been practiced by farmers with little understanding of the reason behind, that

growing a single crop year after year in the same field gives pest populations sufficient time to

become established and build up to damaging levels. Crop rotation interrupts normal life cycle of

insect pests by placing the insects in a non-host habitat. Rotating the field to a different type of

crop can break this cycle by starving pests that cannot adapt to a different host plant. Crop

rotation schemes work because they increase the diversity of a pest's environment and create

discontinuity in its food supply. As a rule, rotations are most likely practical and effective when

they are used against pests that attack annual or biennial crops, have a relatively narrow host

range, cannot move easily from one field to another, and are present before the crop is planted.

Perrin (1977) reported that crop rotation practice worked in the control of white fringed weevil

complex, Graphognathus leucoloma (Boheman) and G. peregrinus (Buchanan), adults which lay

16

many eggs when are fed on soybean and cause heavy damage to this crop. But the grass crops,

including corn, are in some way nutritionally deficient to support feeding, and did not suffer

damage from this pest.

2.4.3.2. Trap cropping

Shelton and Badenes-Perez (2006) reported trap cropping system of field trials undertaken on P.

xylostella as a pest of cabbage but most of the results obtained from the trials were variable from

different regions. Through trap cropping system field trials, several trap crops have been

identified which are able to reduce Diamondback moth infestation on cabbage. Trap cropping

system is most worthwhile for pests that are abundant and destructive in most years like

Diamondback moth. The number of field trials on trap cropping has been tried using single rows

of early-planted trap crop (Michanec, 2003) and perimeter trap cropping against different insect

pests (Boucher, 2003, Boucher and Durgy, 2003). Trap cropping system can be done in two

ways; border (perimeter) trap cropping and row intercropping.

2.4.3.3. Border trap cropping

Border trap cropping system experimental works have been conducted on different crops to test

their effectiveness as trap crops against Diamondback moth. Srinivasan and Krishna (1991)

reported the use of Indian mustard as a trap crop for Diamondback moth in cabbage fields in

Bangalore, India. On the other hand, Silva-Krott et al. (1995) found Indian mustard not attractive

to Diamondback moth in Guam. Nevertheless, Charleston and Kfir (2000) found Indian mustard

to be attractive to Diamondback moth in South Africa and recommended its use as a trap crop in

cabbage.

17

2.4.3.4. Row intercropping

In some crops, intercropping creates discontinuity in the pest's food supply that keeps crops to

remain "out of phase" with pest populations. Several row intercropping field trials conducted

using different intercrops such as tomato, garlic, coriander and carrot to control Diamondback

moth on cabbage revealed that they can reduce the infestation. The intercrops were grown in

alternate rows with cabbage to estimate their influence on Diamondback moth population. The

results reported indicated that the intercropped plots had significantly lower numbers of

Diamondback moth larvae and pupae, and a higher yield of good quality cabbage heads, as

compared to the control (pure stand) cabbage plots. Tomato planted in interrows with cabbage

exhibits deleterious effect on Diamondback moth due to the release of certain volatile chemicals

which have a repellent action on the adults (Sivapragasam and Ruwaida, 1982). Similarly, garlic

in interrows of cabbage also reportedly reduced Diamondback moth infestation (Talekar and

Griggs, 1986). Furthermore, mustard planted in alternate rows reportedly had reduced numbers

of Diamondback moth larvae and pupae on cabbages compared to those planted on pure stand.

Mustard plants have stimulant property due to volatile compounds such as isothiocyanates which

makes Diamondback moth to prefer mustard for oviposition. Apart from lowering insect pest’s

infestation, intercrops can provide additional revenue to the grower, improve soil structure and

soil fertility.

2.4.3.5. Companion cropping

Companion cropping schemes are designed to mask the smell of crop plants by interplating them

with other strong-smelling plants on the basis that insects often locate their host plants by smell.

Morollo-Rejesus (1986) reported that 88 plants have insecticidal properties against Diamondback

moth most of these belonging to the Asteraceaa, Fabaceae and Eurphorbiaceae. Many of such

18

botanicals also have repellent properties although their potential in this role is as yet to be

exploited.

2.4.4. Host plant resistance

Cruciferous crops differ somewhat in their susceptibility to attack by Diamondback moth. The

range of host plants that Diamondback moth attacks is restricted to members of the Brassicaceae

family, which contain glucosinolates that degrade into volatile mustard oils (Salinas, 1986). The

glucosinolates stimulate feeding in P. xylostella, but two of these (3-butenyl and 2-phenylethyl)

are toxic at high concentrations (Nayar and Thorsteinson, 1963). The glucosides sinigrin,

sinalbin and glucocherirolin act as specific feeding stimulants for P. xylostella and 40 plant

species containing one or more of these chemicals serve as hosts.

Many morphological characteristics have been used in plant breeding to reduce pest abundance

and damage. Certain colors are less attractive to certain insects. For example, cabbage worm is

less attracted to red colored Brassica species (cabbages, broccoli, and related species) (Norris

and Marcos, 1980). Mustard, turnip, and kohlrabi are among the more resistant crucifers, but

resistance is not as pronounced as it is for imported cabbage worm and cabbage looper. Varieties

also differ in susceptibility to damage by Diamondback moth, and a major component of this

resistance is the presence of leaf wax. Glossy varieties lacking the normal waxy bloom and

therefore green rather than grayish green are somewhat resistant to larva. Larvae apparently

spend more time searching and less time feeding on glossy varieties (Sanford et al., 1991).

19

2.5. References

Boucher, T. J. (2003). Insect management update for peppers and eggplant. Proceeding of New

England Vegetable and Berry Conference. www.nevbc.org/proceedings.html.

Boucher, T. J. and Durgy, R. (2003). Perimeter trap cropping for summer squash and

cucumbers. Proceedings of New England Vegetable and Berry Conference.

www.nevbc.org/proceedings.html.

Capinera, J. L. (2000). Diamondback moth biology. University of Florida, Institute of Food and

Agricultural Sciences, Department of Entomology and Nematology.

Capinera, J. L. (2000). Handbook of Vegetable Pests. Academic Press, San Diego. 729 pp.

Charleston, D.S. and Kfir, R. (2000). The possibility of using Indian mustard, Brassica juncea as

a trap crop for the Diamondback moth, Plutella xylostella, in South Africa. Crop

Protection 19: 455-460.

Endersby, N. M. and Morgan, W. C. (1991). Alternatives to synthetic chemical insectcides for

use in crucifer crops. Biological Agriculture and Horticulture 8: 33-52.

Godonou I., James, B., Atcha-Ahowé, C., Vodouhè, S. Kooyman,C., Ahanchédé, A. and Korie,

S. (2008). Potential of Beauveria bassiana and Metarhizium anisopliae isolates from

Benin to control Plutella xylostella L. (Lepidoptera: Plutellidae). Crop Protection 28

(3): 220-224.

Gupta, P. D. and Thorsteinson, A. J. (1960). Food plant relationship of diamondback moth

(Plutella maculipennis (Curt.)). I. Gustation and olfaction in relation to botanical

specificity of larvae. Entomologia Experimentalis et Applicata. 3: 241–250.

20

Hartcourt, D. G. (1955). Biology of the diamondback moth, Plutella maculipennis (Curt.)

(Lepidoptera: Plutelladae), in eastern Ontario. Rpt. Quebec Soc. Prot. Plants. 37:155-

160.

Hillyer, R. J. and Thorsteinson, A. J. (1971). Influence of the host plant or males on

programming of oviposition in the Diamondback moth (Plutella maculipennis (Curt.):

Lepidoptera). Canada Journal of Zoology. 49: 983–990.

Lockhart, J. A. R. and Wiseman A. J. L. (1984). Introduction to crop husbandry including

grassland, Fifth edition, Oxford, Pergamon Press. pp. 112.

Löhr, B., Gathu, R., Kariuki, C., Obiero, J. and Gichini, G. (2006). Impact of an exotic parasitoid

on Plutella xylostella (Lepidoptera: Plutellidae) population dynamics, damage and

indigenous natural enemies in Kenya. Bulletin of Entomological Research

(Submitted).

Magaro, J. J. and Edelson, J. V. (1990). Diamondback moth (Lepidoptera: Plutellidae) in south

Texas: a technique for resistance monitoring in the field. Journal of Economic

Entomology 83:1201-06

McHugh, Jr. J. J and Foster, R. E. (1995). Reduction of Diamondback moth (Lepidoptera:

Plutellidae) infestation in head cabbage by overhead irrigation. Journal of Economic

Entomology 88: 162-168.

Michanec, J. (2003). Successful Trap Cropping for Colorado Potato Beetles.

MOA (2006) Ministry of Agriculture, Kenya: Annual Report of year 2005, Nairobi-Kenya.

Momanyi, C. M., Löhr, B. and Gitonga, L. (2006). Biological impact of the exotic of the

parasitoid, Diadegma semiclausum (Hellen), of Diamondback moth, Plutella xylostella

L., in Kenya. Biological Control 38: 254-263.

21

Morollo-Rejesus, B. (1986). Botanical insecticides against the diamondback moth. In: Talekar,

N.S. (Ed.), Diamondback Moth Management. Proceedings of the First International

Workshop, 11–15 March 1985. Asian Vegetable Research and Development Center,

Tainan, Taiwan, pp. 241–255.

Nayar, J. K. and Thorsteinson, A. J. (1963). Further investigations into the chemical basis of

insect host plant relationship in an Oligophagous insect Plutella maculipennis (Curtis)

Lepidoptera: Plutelidae) Canada Journal Zoology 41: 923 – 29.

Nonnecke, L. (1989). Vegetable Production. Norstrand Rinhold, New York, pp 657.

www.nevegetable.org/index.cfm.

Norris, D. and Marcos, K. (1980). Biochemical and morphological bases of resistance. In F.C.

Maxwell and P.R Jennings. (eds.) Breeding plants resistant to insects. New York, John

Wiley and Sons.

Nyasani, O. J., Kimenju, J. W., Olubayo, F. M. and Wilson, M. J. (2008). Laboratory and field

investigation using indigenous entomopathogenic nematodes for biological control of

Plutella xylostella in Kenya. International Journal of Pest Management, 54 (4): 355-

361.

Odour, G. I., Löhr, B. and Seif, A. A. (1996). Seasonality of major cabbage pests and incidence

of their enemies in Central of Kenya. In: Sirvapragragasam, Lim (Eds.), The

Management of DBM and Other Crucifer Pests. Proceeding of the Third International

Oke, O. A. (2008). Evaluation of the effectiveness of three insecticides to control Diamondback

moth (Plutella xylostella) in cabbage (Brassica oleracea var. capiptata L.). European

Journal of Scientific Research. 22: 391-395. Workshop, Kuala Lumpur, Malaysia.

22

Perrin, R. M. (1977). Pest management in multiple cropping systems. Agro-Ecosystems 3:

93Ð118. Proceedings, 2003 New Vegetable Conference.

Rossbach, A., Löhr, B. and Vidal, S. (2006). Generalism versus specialism: responses of

Diadegma mollipla (Holmgren) and Diadegma semiclausum (Hellen), to the host shift

of the Diamondback moth (Plutella xylostella L.) to peas. Journal of Insect Behavior

18: 491-503.

Salinas, P.J. (1986). Studies on Diamond Back moth in Venezuela with reference to other

Latinamerican countries. Diamondback moth management. Poc 1st International

Workshop, Tainan, Taiwan, 11- 15 March 1985 Shanhua, Taiwan; AVRDC, 17 –24.

Sanford, D. E., Karl, E. E. and Shelton A. M., (1991). Behavior of neonate Diamondback moth

larvae [Plutella xylostella (L)] on leaves and on extracte leaf waxes of resistant and

susceptible cabbages. Journal of Chemical Ecology, 17 (8): 1691 – 1704.

Sarfraz, M., Dosdall, L.M. and Keddie, B.A. (2005). Diamondback moth–host plant interactions:

Implications for pest management, Crop Protection: 25 (7) 625-639.

Sarfraz, M. and Keddie B.A., (2005). Conserving the efficacy of insecticides against Plutella

xylostella (L.) Lep., Pltellidae). Journal of Applied Entomology 129: 149-157.

Seraficon, A. (2001). Damage, life cycle, monitoring, pest management and diagnostic guide of

Diamondbackmoth. http: www1.agric.gov.ab.ca/$departement/deptdocs.nsf/all/agdex

2540.

Shelton, A. M., A. Turner, D. Giga, P. Wilkinson, E. Zitzanza, and Utete, D. (1995).

Diamondback moth. Zimbabwe Horticultural Crops Pest Management. NYSAES,

Geneva NY. pp 2.

23

Shelton, A. M. and Badenes-Perez, F. R. (2006). Concepts and applications of trap cropping in

pest management. Annual Review Entomology. 51: 285-308.

Silva-Krott, I. U., Singh, P., Lali, T. S. and Muniappan, R. (1995). Development of a trap

cropping system for cabbage in Guam. Pest Management in Horticultural Ecosystems

1, 28-35.

Srinivasan, K. and Krishna Moorthy, P. N. (1991). Indian mustard as a trap crop for management

of major lepidopterous pests on cabbage. Tropical Pest Management 37: 26-32.

Sivapragasama, T. S. P. and Ruwaida, M. (1982). Effects of intercropping cabbage with tomato

on the incidence of Plutella xylostella. MAPPS Newsletter 6 (2): 6 -7.

Syed, A. R. (1992). Insecticide resistance in the Diamondback moth in Malaysia. Ref. 168, pp.

437-442 in Talekar, N.S. (Ed.) Diamondback moth and other crucifer pests (Ed.

Talekar, N.S.). Proceedings of the Second International Workshop, Tainan, Taiwan, 10

– 14 Dec., 1992, AVRDC

Talekar, N. S. and Griggs, T. D. (1986). Diamondback moth management: Proceedings of the

First International Workshop, 11-15 March 1985, Tainan, Taiwan. 471 pp. Shanhua,

Asian Vegetable Research and Development Center.

Talekar, N. S. (Ed.) (1992). Diamondback moth and other crucifer pests: Proceedings of the

Second International Workshop, 11-15 December 1992, Tainan, Taiwan, Asian

Vegetable Research and Development center.

Talekar, N. S. and Shelton, A. M. (1993). Biology, ecology, and management of the

Diamondback moth. Annual Review of Entomology 38: 275–301

24

Valentine, E. W. (1998). Diamondback moth life cycle. The horticulture and food

research institute of New Zealand.

Varela, A. M., Seif, A. and Löhr B. (2003). A Guide to IPM in Brassicas Production in Eastern

and Southern Africa: International Centre of Insect Physiology and Ecology (ICIPE),

Nairobi, Science Press. pp 95.

25

CHAPTER 3

EVALUATION OF CABBAGE VARIETIES FOR RESISTANCE TO D IAMONDBACK

MOTH ( Plutella xylostella) INFESTATION

3.1. Abstract

This field study was conducted to evaluate varietal resistance of cabbage (Brassica oleracea var.

capitata L.) against Diamondback moth (Plutella. xylostella) infestation and damage at

University of Nairobi farm, Kabete Field Station in two relay cropping 2008 and 2009. Varietal

resistance was compared with conventional spraying using a split plot design whereby spraying

formed the main plot while varieties formed subplots. Dimethoate was preferred insecticide

while cabbage varieties were six; Drumhead, Sugarloaf, Golden Acre, Gloria F1, Copenhagen

Market and Pruktor F1. Sampling was done by weekly counting of larvae and pupae, and scoring

pest damage on five randomly selected plants per plot for 10 weeks from the third week after

transplanting. The numbers of marketable and non-marketable cabbage heads were counted on

all plants per plot at maturity stage. The results showed that sprayed and unsprayed treatments

had significantly (P<0.05) different numbers of Diamondback moth immature (larvae and

pupae). Copenhagen Market and Pruktor F1 had the lowest mean number while Gloria F1 had

the highest records both in sprayed and unsprayed treatments. The highest number of marketable

yield was obtained from Pruktor F1 both in unsprayed and sprayed treatments had 15 and 24

respectively. The study demonstrates that Pruktor F1 can perform better in presence of

Diamondback moth infestation and damage. This variety should be incorporated in an Integrated

Diamondback moth management strategy in Kenya. Its adoption will reduce costs of sprays and

increase farm incomes.

26

3.2. Introduction

Cabbage, Brassica oleracea L. var. capitata is one of the most important vegetables in Eastern

and Southern Africa (Jankowski et al., 2007). In Kenya, production of cabbage is constrained by

insect pests, especially the Diamondback moth. Talekar and Shelton (1993) reported that

Diamondback moth is the most destructive insect pest worldwide to important crucifers and has

severely limited their production, especially in resource-poor regions. With attempts to control

the pest, farmers tend to overuse chemicals, applying high quantities and frequent sprays as well

as use of pesticide cocktails (Varela et al., 2003). Unfortunately, DBM has the ability to quickly

develop resistance to any of the pesticides which extensively used against it (Gelernter and

Lomer, 2000). There is need, therefore, to diversify control options for Diamondback moth on

cabbage and minimize dependency on pesticides usage. Such options include use of host plant

resistance (HPR), which has potential to contain Diamondback moth infesting Crucifer, such as

cabbage (Brassica oleracea L. var. capitata), broccoli (B. oleracea var. italica) and cauliflower

(B. oleracea var. botrytis) (Hamilton et al., 2005). There is evidence to suggest that larval

feeding or survival may be reduced in normal-bloom varieties through antixenosis (Verkerk and

Wright, 2008). Hamilton et al. (2005) expressed an immediate need and pragmatic challenge to

identify the currently available most resistant cabbage cultivars. Host location and oviposition

are crucial steps in the life cycles of insect herbivores. Immature stages of Lepidoptera, such as

Diamondback moth and the cabbage white butterfly, Pieris rapae (L.) (Lepidoptera: Pieridae),

both pests of brassicas vegetable crops, are relatively immobile and dependent on the ability of

the adult female to choose a suitable host plant (Renwick and Chew, 1994). This study aimed at

identifying varietal resistance among cabbage varieties against Diamondback moth infestation

and damage.

27

3.3. Material and methods

The study was carried out at Kabete Campus Field Station Farm, University of Nairobi, in two

relay cropping from September to December 2008 and December 2008 to March 2009. The six

cabbage varieties evaluated were Drumhead, Sugarloaf, Golden Acre, Gloria F1, Copenhagen

Market and Pruktor F1. The experiment was laid in a split plot design with main plot consisting

of pesticide application (sprayed and unsprayed) and subplots consisting of cabbage varieties.

The variety treatments were replicated four times. Each subplot was 3 x 3 m separated by 1 m

guard row between plots and 2 m between replications. The main plots were separated by 3 m

guard row. One month old cabbage seedlings were transplanted in a ploughed and fine tilled field

spaced at 60 x 60 cm to keep uniformity. During transplanting (Diammonium Phosphate) D.A.P.

fertilizer was applied at rate of 20 g per planting hole. The crop was hand-weeded two weeks

after transplanting and there after every two weeks. After one month of transplanting, top

dressing was done at rate of 20 grams per seedling using Calcium Ammonium Nitrate (C.A.N)

(23%N). Dimethoate was sprayed with a knapsack sprayer at a rate of 20 ml in 25 liters of water

once per week just after every data collection, which was done weekly for 10 weeks. Five plants

in each plot were randomly sampled during each sampling from third week of transplanting up to

the 10th week to record the immature Diamondback moth (larvae and pupae) and crop damage

insitu. The pest damage was scored using a modified scale of 1 to 5, adopted after Dreyer (1987)

(Table 1). The numbers of marketable and unmarketable cabbage heads were counted from each

plot at the end of the experiment and at the same time the weight of marketable cabbage yield

was measured. The experiment was conducted under rainfed but during dry periods irrigation

was required to keep soil moisture. All the data collected were subjected to Analysis of variance

(ANOVA) using GENSTAT Discovery Edition after square root transformation [(x + c)**0.05]

28

and correlation analyses were done using the same program. Means were separated using least

significant difference (LSD) at P = 0.05.

Table 3.1. Cabbage damage score scale used at Kabete Field Station in 2008 and 2009 plantings.

Scores Description

1 No damage, or few isolated small holes in the outer or lower leaves

2 Many holes but damage limited to outer or lower leaves

3 Considerable damage of the outer or lower leaves, slight damage on the cabbage

head, head marketable with minor leaf removal of outer head leaves

4 Outer or lower leaves completely destroyed, moderate attack of inner leaves,

head marketable after considerable removal of outer head leaves

5 Severe attack on the head (head unmarketable)

Source: Modified scale, adopted after Dreyer, (1987).

3.4. Results

3.4.1. Immature Diamondback moth infestation and fluctuation trends

The trend of Diamondback moth immature during the two cropping period in both sprayed and

unsprayed plots were similar (Figure 3.1). However, their populations were significantly

(P<0.05) lower in sprayed plots compared with unsprayed plots.

29

Figure 3.1. Mean number of immature Diamondback moth on sprayed and unsprayed cabbage

varieties at Kabete Field Station.

The infestations by Diamondback moth immature was significantly was significantly different

(P<0.05) between sprayed and unsprayed varieties. Unsprayed varieties had higher infestations

compared with sprayed varieties, as expected priori. From the two cropping period, Pruktor F1

and Copenhagen Market both sprayed and unsprayed treatment had significantly (P<0.05) lower

number of Diamondback moth immature compared with other varieties (Table 3.2). The highest

mean number of Diamondback moth immature was recorded in plots planted with Gloria F1.

30

Table 3.2. Mean number of immature Diamondback moth on the sprayed and the unsprayed

cabbage varieties at Kabete Field Station.

Mean number of immature DBM/5 plants Treatments Unsprayed Sprayed Pruktor F1 3.68 2.85 Copenhagen Market 4.33 2.58 Sugarloaf 4.5 3.26 Drumhead 4.68 3.4 Golden Acre 4.7 3.04 Gloria F1 5.15 3.53 Mean 4.51 3.11 LSD(p = 0.05) 0.28 0.25 P value 0.030 0.187

3.4.2. Diamondback moth damage levels

There was significant difference (P<0.05) on levels of damage among cabbage varieties in the

sprayed and unsprayed treatments (Table 3.3). The highest damage was recorded in unsprayed

varieties compared with sprayed varieties. Varieties Pruktor F1 and Sugarloaf had lowest

damage level while the highest damage level were scored in Copenhagen Market and Drumhead

variety in unsprayed and sprayed respectively. The interaction of varieties and the insecticide

treatments did not show significant difference (P>0.05) in the DBM infestation.

31

Table 3.3. Mean damage scores by Diamondback moth on cabbage varieties at Kabete Field

Station.

Mean damage scores/5 plants Treatments Unsprayed Sprayed Sugarloaf 1.45 1.26 Pruktor F1 1.60 1.30 Golden Acre 2.56 2.03 Drumhead 2.60 2.11 Gloria F1 2.65 2.03 Copenhagen Market 2.85 1.94 Mean 2.29 1.78 LSD(p = 0.05) 0.11 0.13 P value 0.001 0.001

3.4.3. Yield

Cabbage varieties showed significant differences (P<0.05) in terms of marketable and

unmarketable yields between sprayed and unsprayed varieties (Table 3.4). Among unsprayed

varieties, Pruktor F1 and Copenhagen Market recorded highest number of marketable cabbage

heads while the highest number of unmarketable cabbage heads was obtained from Gloria F1.

However, among sprayed varieties, the highest number of marketable cabbage heads was

recorded in Pruktor F1 while the lowest number of marketable cabbage heads was recorded in

Golden Acre. There was no significant difference (P>0.05) on unmarketable cabbage heads

among sprayed varieties.

32

Table 3.4. Mean number of marketable and unmarketable cabbage heads per variety at Kabete

Field Station.

Mean number of marketable and unmarketable cabbage heads Marketable Unmarketable Treatments Unsprayed Sprayed Unsprayed Sprayed Sugarloaf 13.00 15.00 10.00 9.00 Pruktor F1 15.00 24.00 11.00 8.00 Golden Acre 6.00 8.00 12.00 5.00 Drumhead 9.00 18.00 10.00 7.00 Gloria F1 11.00 17.00 16.00 11.00 Copenhagen Market 15.00 21.00 10.00 5.00 Mean 12 17 11 11 LSD(p = 0.05) 4.26 5.69 5.84 2.04 P value 0.001 0.001 0.160 0.001

In terms of the weight of marketable cabbage heads, Pruktor F1 had highest, followed by

Copenhagen Market both in unsprayed and sprayed varieties, (Table 3.5). Golden Acre had the

lowest marketable cabbage yield among sprayed varieties while among unsprayed varieties

lowest marketable cabbage yield (Kg) was recorded in Drumhead variety.

Table 3.5. Mean yield of marketable cabbage heads (Kg) at Kabete Field Station.

Mean cabbage weights (Kg) Treatments Unsprayed Sprayed Pruktor F1 9.70 12.40 Copenhagen Market 8.33 11.97 Gloria F1 6.75 8.50 Golden Acre 6.15 5.45 Sugarloaf 5.98 9.55 Drumhead 5.75 6.43 Mean 7.11 9.00 LSD(p = 0.05) 7.11 9.48 P value 0.810 0.559

There was a significant (P<0.05) positive correlation between the mean number of immature

Diamondback moth and damage scores recorded on cabbages (Table 3.6.).

33

Table 3.6. Relationship between immature Diamondback moth and damage scores on cabbage

heads at Kabete Field Station.

Damage Scores DBM immature Damage Scores 1.00 0.240** DBM immature 0.240** 1.00

**Correlation is significant at 0.05 level (two tailed)

3.4. Discussion

This study showed that Pruktor F1 hybrid and Copenhagen Market varieties had the lowest mean

numbers of immature Diamondback moth compared with other cabbage varieties both when the

crop was sprayed and when it was not sprayed. The immature Diamondback moth population

increased in numbers when higher temperatures were experienced but it appears that rainfall

influenced pest population to drop drastically. The impact of rain or irrigation water drops on

diamondback moth eggs and larvae have been reported by several researchers that they can result

to wash off of the Diamondback moth eggs from cabbage leaves and may increase mortality on

larvae (Ali et al., 2007). In her study Wainganjo (1990) reported that Red Acre and Gloria F1

cabbage varieties had the least Diamondback moth immature numbers within the unsprayed

cabbage varieties per plant while Copenhagen Market cabbage variety had the highest number of

immature Diamondback moth. In this present study, Pruktor F1 cabbage hybrid was the less

preferred variety followed by the Copenhagen Market variety when compared with other

cabbage varieties within the unsprayed treatment since they had the lowest mean number of the

immature Diamondback moth. Pruktor F1 and Copenhagen Market cabbage variety which gave

higher marketable cabbage heads can be recommended for Diamondback moth management in

combination with other Integrated Pest Management strategies. Since the results obtained from

this study indicated differences on the level of infestation among cabbage varieties, it shows that

34

varieties differ in susceptibility to damage by Diamondback moth. This implies that those

varieties might contain higher content of glucosinolates which is known to act as potent for

ovipositing and feeding stimulant for more than 25 insect species in the Coleoptera, Lepidoptera

and Diptera that are specialized on brassicaceous plants (Hopkins et al., 2009). Resistant cabbage

varieties which have leafy waxes could be effective in influencing the searching behavior of

neonate Diamondback moth larvae as they will spend more time looking for suitable leaves.

Other studies have reported that the pest tends to spend more time on searching rather than

feeding when the plant contains higher leaf waxes (Sanford et al., 1991). Cabbage varieties

sprayed with Dimethoate had lower mean number of larvae compared with unsprayed varieties

as expected. Although several farmers use synthetic insecticides like Dimethoate for controlling

Diamondback moth, the insecticide is unsuitable due to its phytotoxicity and toxicity to

beneficial insects such as natural enemies or other living organisms in the environment and result

in additional cost of production. Cabbage varieties with higher mean number of immature

Diamondback moth had higher mean number of damage scores. This lead to having lower

number of marketable cabbage heads on the sprayed and the unsprayed cabbages while the

number of the recorded unmarketable cabbage heads increased. This implies that any changes in

the number of the Diamondback moth immatures can cause significant changes in damage level

on cabbage heads. It therefore can be implied that cabbage resistant varieties could be used by

farmers in combination with other recommended control methods to produce cabbage heads of

high quality.

35

3.5. References

Ali, G., Karim, K., Yaghoub, F. and Habib, A. (2007). Temperature-dependent development of

Diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) on two

brassicaceous host plants. Journal of Insect Science, 14: 309-316.

Dreyer, M. (1987). Field and laboratory trials with Neem products as protectants against pests of

vegetable and field crops in Togo. In: Schmutterer, H., Ascher, K. R. S. (Eds.), Natural

pesticides from the Neem Tree (Azadirachta indica A Juss). Proceedings of the Third

International Neem Conference, 10- 15 July 1986. GTZ, Eschborn, FRG, Nairobi,

Kenya, pp 431- 447.

Gelernter, W. D. and Lomer, C. J. (2000). Success in biological control of above ground insects

by pathogens. In: Gurr, G. and S. Wratten (eds) Biological Control: Measures of

Success. Dordrecht, Kluwer Academic Publisher, 297-322.

Hamilton J. A., Endersby M. N., Ridland P. M., Zhang J. and Neal, M. (2005). Effects of cultivar

on oviposition preference, larval feeding and development time of Diamondback

moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), on some Brassica oleracea

vegetables in Victoria. Australia Journal of Entomology, 44: 284-287.

Hopkins, R. J., van Dam, N. M. and van Loon J. J. A. (2009). Role of glucosinolates in insect-

plant relationships and multitrophic interactions. Annal Review of Entomology, 54: 57-

83.

Jankowski, A., Mithöfer D., Löhr B., Waibel, H. (2007). Economics of biological control in

cabbage production in two countries in East Africa. University of Kassel-

Witzenhausen and University of Göttingen, Conference on International Agricultural

Research for Development, October 9-11, 2007.

36

Renwick, J. A. A. and Chew, F.S. (1994). Oviposition behaviour in Lepidoptera. Annual Review

of Entomology, 39: 377–400.

Sanford, D. E., Karl, E. E. and Shelton A. M., (1991). Behavior of neonate Diamondback moth

larvae [Plutella xylostella (L)] on leaves and on extracte leaf waxes of resistant and

susceptible cabbages. Journal of Chemical Ecology, 17 (8): 1691 – 1704.

Talekar, N.S. and Shelton, A. M. (1993). Biology, ecology and management of the Diamondback

moth. Annual Review of Entomology, 38: 275-301.

Varela, A. M., Seif, A. and Löhr, B. (2003). A Guide to IPM in Brassicas Production in Eastern

and Southern Africa: International Centre of Insect Physiology and Ecology (ICIPE)

Science Press, Nairobi., pp 21.

Verkerk, R. H. J., and Wright, D. J. (2008). Interactions between the Diamondback moth,

Plutella xylostella L. and glasshouse and outdoor-grown cabbage cultivars. Annals of

Applied Biology, 125: 477-488.

Wainganjo, M. M. (1996). The Biology and Ecology of the Diamondback moth, Plutella

xylostella L. with special Reference to susceptibility of six cabbage varieties grown in

Kenya. MSc. Thesis, University of Nairobi, Kenya.

37

CHAPTER 4

EVALUATION OF BORDER CROPS ON THE DIAMONDBACK MOTH (Plutella

xylostella) INFESTATION AND THE DAMAGE OF CABBAGE ( Brassica oleracea var.

capitata)

4.1. Abstract

Different trap crops were evaluated to determine their effectiveness to reduce Diamondback

moth infestation on cabbage. Tomato, Kale, Indian mustard, Coriander, Cleome and Radish were

planted around cabbage var. Copenhagen Market plots to pull or push Diamondback moth away

from the cabbage. The field experiment was carried out in two relay cropping of 2008 and 2009

at Kabete Field Station Farm, University of Nairobi, Kenya. Border crops were planted 15 days

prior to cabbage transplanting to facilitate cabbage protection around the whole plot. The

experiment was set in a Randomised Complete Block Design. The counts of larvae, pupae and

damage scores were recorded insitu on five randomly selected cabbage plants per plot. Cabbage

heads were classified either of marketable or unmarketable depending on level of damage.

Sampling started at third week of cabbage transplanting and continued weekly for eight weeks.

Results show that there was significantly (P<0.05) lower number of Diamondback moth

immatures in cabbage surrounded with Indian mustard compared with other types of border

crops. In addition, there was significant difference between marketable and unmarketable

cabbage heads among the border crops. Cabbage from plots bordered with Indian mustard

(32.25) and Coriander (29.00) had highest mean number of marketable yield. These two border

crops were more effective on reducing Diamondback moth infestation. Farmers are advised to

incorporate them in management of Diamondback moth in the field. Other than protecting

cabbage form the target pests, these border crops can also provide farmers with income.

38

4.2. Introduction Cabbage (Brassica oleracea var. capitata) suffers huge yield and quality losses caused by insect

pests mainly Lepidopteran species particularly Diamondback moth (Plutella xylostella). Most

ovipositing Lepidopterans prefer to lay their eggs on hosts where their larvae are able to survive

(Francisco et al., 2004). In the warm humid tropics, Diamondback moth breeds throughout the

year, and can have more than ten generations annually (Facknath, 1997). Larvae of P. xylostella

cause significant losses in terms of marketable yield and hence family income. However,

Diamondback moth can cause serious damage even with application of several different

insecticides because of its ability to develop resistance to almost all insecticides (Shelton et al.,

1993). The insecticide resistance by Diamondback moth has made the pest the focus of IPM

research in many parts of the world. The negative impacts of pesticides and increasing pesticide

resistance capacity on DBM have increased the interest in alternative control methods, with

emphasis on biological control, plant resistance, cultural control and other non-polluting methods

(Lim et al., 1996). Use of trap crops could reduced the pest damage and number of sprays needed

to produce economic crop since they can push or pull away pests from the main crop (Francis,

2001). Trap crop system is especially important in subsistence farming, practiced mainly in

developing countries due to its ability to reduce reliance on pesticides and also lower production

costs (Hokkanen, 1991).

In some areas, farmers inter-crop cabbage with other brassica crops or crucifer weeds that are

more attractive to DBM than cabbage. Mitchell et al. (2000) found that collards attracted more

Diamondback moth’s larvae in the cabbage fields which made trap cropping with collards a

popular practice in the United States of America. Similarly, Charleston and Kfir (2000) found

more egg laying, but low survival rate of the larvae on Indian mustard used as a trap crop.

39

However, Indian mustard failed to reduce DBM infestation in several other countries like

Taiwan, South East Asia and Canada (Talekar, 1996). But to the contrary, in South Africa where

the DBM crop preference is not known, the Indian mustard was found to have potential to act as

a trap crop for Diamondback moth (Charleston and Kfir, 2000). This study was done to evaluate

effectiveness of six trap crops to reduce infestation and damage of cabbage by Diamondback

moth.

4.3. Material and methods

The study was carried out at Kabete Campus Field Station Farm, University of Nairobi, between

September 2008 to December 2008 and January 2009 to April 2009. The soils are well-drained,

very deep, reddish brown to dark red (Nitosols) developed from Limuru Trachite (Michieka,

1977). Border crops evaluated were three host plants from brassicas family; Indian mustard

(Brassicas juncea), Kale (Brassica oleracea var. acephala) and Radish (Raphanus sativus L.

hortensis) and other three no-host plants from Solanaceae; Tomatoes (Solanaceorum esculentum

var. Rio grande), Capparidaceae; Coriander dhania (Coriandrum sativum) and Apiaceae; Cleome

(Cleome gynandra L.) plant families The control treatment was the cabbage bordered with fallow

land, which was kept weed free throughout the season. All border crops were established in the

field 15 days before transplanting cabbage seedlings. The experiment was laid in a Randomized

Complete Block Design (RCBD) four replicates in plot sizes of 4.0 x 4.0 m. An alley of 1 and 2

m was maintained between plots and blocks, respectively. The intra-row spacing for border crops

was; 10 cm Coriander, 15 cm Indian mustard, 20 cm Radish, 25 cm Kale, 45 cm Tomatoes, and

45 cm Cleome. One month old cabbage seedlings were transplanted in ploughed and fine tilled

plots spaced at 60 cm inter-row and 45 cm intra-row surrounded by the different border cropping

treatments. During transplanting D.A.P fertilizer was applied at rate of 20 g per planting hole.

40

After one month of transplanting, top dressing was done at rate of 20 g per seedling using

Calcium Ammonium Nitrate (C.A.N) (23% N). Plots and alleys were kept weed free manually

throughout the season. Sampling was done by counting numbers of immature Diamondback

moth (larvae and pupae) and scoring damage (Table 1) on five randomly selected cabbage plants

per plot insitu. Sampling was done weekly from week 3 after transplanting for 8 weeks and

different plants were sampled each time. The number and weight of marketable and

unmarketable cabbage heads were recorded during harvesting at the maturity stage. The cabbage

weights from different varieties were recorded only on cabbage heads categorised as marketable

among others. All the data collected were subjected to Analysis of variance (ANOVA) using

GENSTAT Discovery Edition after square root transformation [(x + c)**0.05] and correlation

analyses were done using the same program. Means were separated using least significant

difference (LSD) at P = 0.05.

4.4. Results

4.4.1. Diamondback moth infestation and fluctuation trends

The level of immature Diamondback moth (larvae and pupae) infestation varied significantly

(P<0.05) during the sampling periods in the two plantings (Figure 4.1). In the first planting, the

highest mean number of the immature Diamondback moth were recorded during the seventh

sampling after transplanting while in the same week of the second planting, there was a sudden

drop in the mean numbers of immature DBM.

41

Figure 4.1. Mean number of immature Diamondback moth on cabbage plots surrounded by

different border crops at Kabete Field Station.

There was significant difference (P<0.05) among the different border cropping treatments on

immature Diamondback moth infestation level both in first and second cropping (Table 4.1). The

lowest mean numbers of immature Diamondback moth were recorded on cabbage bordered by

Indian mustard among the border crops of crucifer family while Coriander had the lowest among

non crucifer crops. The results did not show any significant difference at (P>0.05) on the

interaction between sampling times and treatments.

42

Table 4.1. Mean number of the immature Diamondback moth on cabbages surrounded by

different border crops at Kabete Field Station.

Immature Diamondback moth Treatments Planting 1 Planting 2 Fallow 5.41 6.31 Cleome 5.19 3.50 Coriander 3.66 4.59 Indian mustard 2.88 2.22 Kale 4.00 3.88 Radish 3.16 4.69 Tomato 4.38 3.88 Mean 4.09 4.15 LSD(p = 0.05) 0.29 0.31 P value 0.001 0.001

4.4.2. Diamondback moth damage levels

The results indicated that there was significant difference (P<0.05) on damage of cabbage among

border crops in the two plantings (Table 4.2). Cabbage plots bordered with Indian mustard had

lowest damage scores whereas the highest damage score was recorded on the control treatment.

Plots bordered with the non hosts did not significantly (P>0.05) differ from each other in the

damage rating. The damage levels were lower in second planting compared with the first

planting. However, the results did not show significant interaction (P>0.56) between sampling

time and border crops on the cabbage damage.

43

Table 4.2. Mean damage scores on cabbage surrounded by different border crops at Kabete

Field Station.

Damage scores Treatments Planting 1 Planting 2 Fallow 2.94 2.56 Cleome 2.06 1.63 Coriander 2.13 1.59 Indian mustard 1.56 1.03 Kale 1.69 1.25 Radish 2.22 1.59 Tomato 2.22 1.47 Mean 2.12 1.60 LSD(p = 0.05) 0.15 0.11 P value 0.001 0.001

4.4.3. Yield

The results showed significant differences (P<0.05) in the numbers of marketable and

unmarketable cabbage yield from the plots surrounded with different border crops (Table 4.3).

Plots bordered by Indian mustard, Radish and Coriander had the highest mean numbers of the

marketable cabbage yield compared with other treatments. The other treatments were recorded

with the highest mean numbers of unmarketable cabbage yield.

44

Table 4.3. Mean number of marketable and unmarketable cabbage heads at Kabete Field Station.

Mean cabbage heads Treatments Marketable heads Unmarketable heads Fallow 9.00 33.50 Cleome 19.00 16.50 Coriander 29.00 12.00 Indian mustard 32.25 10.00 Kale 22.50 13.20 Radish 25.25 15.00 Tomato 20.25 16.80 Mean 22.46 16.70 LSD(p = 0.05) 0.80 1.11 P value 0.001 0.001

The highest marketable cabbage weights were obtained in plots bordered with Indian mustard,

Radish and Coriander which incidentally had highest number of marketable heads (Table 4.4).

The control treatment had the highest weight of unmarketable heads compared with other

treatments.

Table 4.4. Mean weights (Kg) of marketable and unmarketable cabbage heads from plots

surrounded with different border crops at Kabete Field Station.

Mean cabbage weight (Kg) Treatments Marketable Unmarketable Fallow 15.30 9.32 Cleome 10.70 3.20 Coriander 22.00 5.07 Indian mustard 33.20 3.57 Kale 16.80 3.07 Radish 23.20 3.60 Tomato 15.00 5.02 Mean 19.50 4.70 LSD(p = 0.05) 1.39 0.69 P value 0.025 0.090

The results showed a positive relationship between the mean numbers of the immature

Diamondback moth and the mean damage scores on cabbage heads (Table 4.5).

45

Table 4.5. Relationship between immature Diamondback moth and damage scores on cabbage

heads at Kabete Field Station.

Damage Scores DBM immature Damage Scores 1.00 0.125** DBM immature 0.125** 1.00

**Correlation is significant at the 0.05 level (two tailed)

4.5. Discussion Cabbage plots bordered with Indian mustard and Coriander had the lowest mean numbers of the

immature Diamondback moth on Copenhagen Market cabbage varieties. The border crop,

coriander most likely repelled (pushed away) adult Diamondback moths such that they did not

lay eggs on the main crop. The few Diamondback moth eggs that hatched on cabbage resulted to

having fewer larvae; but since these larvae caused high damage, it implies that Coriander did not

interrupt their feeding. Cabbage heads from the plots bordered with Indian mustard had the

lowest damage level which shows that the Indian mustard border crop most likely have attracted

the Diamondback moth females for oviposition thus, it was the most preferred host for eggs

laying compared with cabbage. The lower damage level on cabbage heads bordered by Indian

mustard is in conformity with the report by Francisco et al. (2004) that Diamondback moth

prefers to lay eggs on mustard compared with cabbage although it results in low survival rate of

the larvae on mustard. Shelton et al. (2007) reported the potential use of mustard as a dead-end

trap crop of P. xylostella regardless of whether it is a Bacillus thurigiensis (Bt)-transgenic or not

because it is more attractive for oviposition than the cash crop. In other studies, mustard

intercrop had also significantly reduced diamondback moth infestation in the field (Raini et al.,

2002). Coriander did not support the feeding and development of Diamondback moth. The

control plot attracted the highest number of Diamondback moth to lay eggs on cabbages which

46

resulted in higher mean number of larvae and damage level as compared with other treatments.

Plots with the Indian mustard border crop produced the highest marketable cabbage heads with

the highest weights compared with other border crops. The control treatment had the highest

mean number of unmarketable cabbage heads compared with other treatments. This implies that

among those border crops better quality cabbage heads can be obtained with the growing of

cabbages surrounded by one of those border crops. Broad et al. (2008) reveals that the success of

crop diversionary strategies through cropping systems such as border crops depends on the

relative ability of the target herbivore to locate its host plant and the scale of diversity rather than

diversity itself. However, in Kenya the potential of diversification by use of border cropping

system has been also reported on the management of Aphids with pigeon peas border crop that

reduced infestation on okra (Abelmoschus esculentus) by maintaining the pest below economic

damage level (Nderitu et al., 2008). Cabbage damage by Diamondback moth depends positively

on the number of the available immature DBM such that the more they are the more damage on

cabbage heads. Therefore, those border crops, such as the Indian mustard and Coriander, which

performed better, can be used for the management of Diamondback moth infestation on cabbage.

4.6. References

Broad, S. T., Schellhorn, N. A., Lisson, S. N. and Mendham, N. J. (2008). Host location and

oviposition of lepidopteran herbivores in diversified broccoli cropping systems.

Agricultural and Forest Entomology, 10, (2): 157-165.

Charleston, D. S. and Kfir, R. (2000). The possibility of using Indian mustard, Brassica juncea,

as a trap crop for the Diamondback moth, Plutella xylostella, in South Africa. Crop

Protection, 19: 455–460.

47

Facknath, S. (1997). Study of botanical pesticides in Mauritius. Proc. Expert Group Meeting on

risk reduction in agrochemical development in the Afro-Arab region. Dec. 1996,

Mauritius.

Francis, R. (2001). Biological control of Diamondback moth in cabbage production, 2000 –

2001CUIPM Grants – Final reports, County Extension Agent, Commercial

Agriculture, Aquaculture, Clemson Extension Services.

Francisco, R. B., Shelton, A. M. and Nault, B. A. (2004). Evaluating trap crops for Diamondback

moth, Plutella xylostella (Lepidoptera: Plutellidae). Journal of Economic Entomology,

97: 1365–1372.

Hokkanen, H. (1991). Trap cropping in pest management. Annal Review of Entomology, 36:

119–138.

Raini, R. K., Mueke, J. M. and Sithananatham, S. and Agong, G. S. (2002). The influence of

selected companion crops on Diamondback moth (Plutella xylostella L.) development

and infestation on cabbage: Demand – driven agricultural research for sustainable

natural resource base, food security and incomes. Proceedings of the 8th Biennial

Scientific Conference. Kenya Agriculture Research Institute. pp 181 – 186.

Lim, G. S., Sivapragasam, A. and Loke, W. H. (1996). Crucifer insect pest problems: trends

issues and management strategies. In: The Management of Diamondback Moth and

other Crucifer Pests: Proceedings of the Third International Workshop, October 1996,

Kuala Lumpur, Malaysia. Malaysian Agriculture Research and Development Institute,

pp. 3 -16.

Michieka, D.O. (1977). Soils of valley bottom of Kabete Vet Labs, Nairobi. Site evaluation

report. Kenya Soil survey, Nairobi.

48

Mitchell, E. R., Ho, G. G. and Johanoswicz, D. (2000). Management of Diamondback moth

(Lepidoptera : Plutellidae) in cabbage using collard as a trap crop. Horticultural

Science, 35: 875-879.

Nderitu, J., Kasina, M. and Malenge, F. (2008). Evaluating border cropping system for

management of Aphids (Hemiptera: Aphididae) infesting Okra (Malvaceae) in Kenya.

Journal of Entomology, 5(4): 262-269.

Sayyed, A. H., Rizvi, M. R. and Alvi, H. H. (2002). Management of Diamondback moth,

Plutella xylostella (Lepidoptera) (Plutellidae): a Lesson from South East Asia for

Sustainable Integrated Pest Management. Pakistan Journal of Biological Science 5:

234-245.

Shelton, A. M., Hatch, S. L., Zhao, J. Z., Chen, M., Earle, E. D. and Cao, J. (2007). Suppression

of Diamondback moth using Bt-transgenic plants as a trap crop. Crop Protection, 27:

403-409.

Shelton, A. M., Wyman, J. A., Cushing, N. L., Apfelbeck, K., Dennehy, T. J., Mah, S. E. R. and

Eigenbrode, S. D. (1993). Insecticide resistance of the Diamondback moth in North

America. Journal of Economic Entomology, 86: 11 -19.

Talekar, N. S. (1996). Biological control of Diamondback moth in Taiwan – a review. Plant

Protection Bulletin Taipei, 38: 167 – 189.

49

CHAPTER 5

GENERAL DISCUSION, CONCLUSIONS AND RECOMMENDATIONS

5.1. General Discussion

This study evaluated cabbage varieties and border crops to identify resistant cabbage varieties

and effective border crops to make a contribution in the development of an integrated pest

management of Diamondback moth. Use of resistant cabbage varieties and border crops are

some of the cheapest cultural pest control strategies that can be adopted by farmers. Resistant

varieties are important in farming because they have the ability to grow and produce

economically, despite the presence of the pest (Fenemore and Prakash, 2006). The study on the

Cabbage varieties revealed that some varieties confer resistance to Diamondback moth

infestation resulting in low damage of the cabbages which were able to be considered for

marketing. It was also evident that different border crops had significant influence on the

Diamondback moth infestation and damage on cabbage.

Cabbage variety Pruktor F1 and Copenhagen Market were infested with lower numbers of

immature DBM which is responsible for cabbage head damage. Consequently, the same varieties

were also found to have higher numbers of marketable cabbages even in unsprayed varieties.

Although Dimethoate was used in this study, such insecticide needs to be discouraged for use

among farmers. The insecticide has a lot of disastrous impact on the natural populations of

beneficial insects implying that it would interfere with other integrated pest management

components. Jankowski et al. (2007) indicated a serious need for reducing use of insecticides on

cabbage but rather to rely on biological control for managing Diamondback moth since it results

in health benefits to farmers and has positive effects on the environment. The combination of

50

resistant cultivars with other appropriate integrated pest management programmes pose no

technical difficulties to the farmer and are environmentally friendly (Wambua, 2004). In

addition, insect-resistant varieties form an important component of integrated pest management

programs (Sarfraz et al., 2006).

The cabbage plots surrounded with Indian mustard and Coriander that had the lowest mean

numbers of immature DBM reveals that these border crops attracted and repelled respectively the

pest from the main crop. Previous study by Kahuthia-Gathu et al. (2008) reported similar

ovipositing preference on wild crucifers, where Indian mustard belongs, compared to cabbage

and kales. This is an indication that farmers can use Indian mustard border crops to reduce

Diamondback moth infestation. Although some host and non-host border crops did not

significantly reduce infestation and damage compared to the Indian mustard, it can be deduced

that they had some effect on the pest compared with the control treatment. With this knowledge,

the Indian mustard border crop, Copenhagen Market and Pruktor F1 can be effectively used in

controlling Diamondback moth with less or no much spending on pesticides and at the same time

obtaining good yield.

5.2. Conclusions

This study revealed that some cabbage varieties and border crops have potential for reducing

Diamondback moth infestation and cabbage damage levels. Among the sprayed and unsprayed

cabbage variety, Copenhagen Market and Pruktor F1 had the lowest infestation and produced

higher numbers of marketable cabbage heads. The Indian mustard border crop was the most

efficient border crop in the reduction of Diamondback moth infestation and damage on cabbage

heads. It was evident from the results that the Indian mustard border crop would improve

51

cabbage production since higher numbers of marketable cabbage heads were recorded from plots

bordered with the Indian mustard. The use of these cultural control methods is affordable to

farmers since they do not require extra investment on new farming technologies.

5.3. Recommendations

i. Cabbage varieties, Copenhagen Market and Pruktor F1 are more useful for production

since they have high possibility to give better yield and cabbage heads of good quality

for marketing.

ii. Farmers can grow cabbage bordered with the Indian mustard plants to reduce

Diamondback moth infestation and damage levels.

iii. Further studies should continue to evaluate new cabbage varieties in the market to assist

the farmers to identify the best varieties in terms of resistance and quality.

iv. Further research work on border crops will be needed to look into their impact on yield

improvement and socio-economic standard of farmers.

v. Further research work on cabbage insect-resistant varieties needed to indentify

antixenosis factors.

52

5.3. References

Fenemore, P. G. and Prakask, A. (2006). Applied Entomology. New Age publishers, Delhi pp

117.

Kahuthia-Gathu, R., Löhr, B. and Poehling H. M. (2008). Development of reproductive potential

of Diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) on cultivated and

wild crucifer species in Kenya. International Journal of Tropical Insects Science 28:

19-29.

Jankowski, A., Mithöfer D., Löhr B. and Waibel, H. (2007). Economics of Biological Control in

Cabbage Production in two countries in East Africa. University of Kassel-

Witzenhausen and University of Göttingen, Conference on International Agricultural

Research for Development, October 9-11, 2007.

Sarfraz, M., Dosdall, L.M and Keddie B.A. (2006). Diamondback moth–host plant interactions:

Implications for pest management. Crop Protection 25: 625–639.

Wambua, E. M. (2004). Evaluation of varietal resistance and pesticides as management of

strategies for thrips (Megarulothrips sjostedti Trybom and Frankliniella occidentalis

Pergrande) on French beans (Phaseolus Vulgaris L.). MSc. Thesis, University of

Nairobi, Kenya.