ELSEVIER Industrial Crops and Products 5 (1996) 307-322

INDUSTRIAL CROPS AND PRODUCTS

AN INTERNATIONAL JOURNAL

Pyrethrum (Chrysanthemum cinerariaefolium Vis.) cultivation in West Kenya: origin, ecological conditions and management

F? Wandahwa a, E. Van Ranst a,*, I? Van Damme b

a University of Ghent, Department of Geology and Soil Science, Laboratory of Soil Science, Krijgsluan 281/S8, 9000, Ghent, Belgium b University of Ghent, Faculty of Agricultuml and Applied Biological Sciences, Department of Crop Production, Coupure Links 653,

9000, Ghent, Belgium

Received 17 April 1996; accepted 8 July 1996

Abstract

Pyrethrum (Chrysanthemum cineruriaefoZium) is a small perennial plant commercially grown for extraction of natural pyrethrins used to make insecticides. This paper discusses the use and distribution of pyrethrum, the ecological requirements and agronomic practices in West Kenya, with emphasis on management constraints and further research. The responses to nitrogen, phosphorus and potassium fertilizers are reviewed. These responses are not yet well understood and require further research. Diseases, pests and weeds of pyrethrum and their control are mentioned. Further research on application of herbicides is required. Farmers grow pyrethrum in less favourable climatic conditions. Yields are low and influenced by producer prices. Research should therefore focus on increasing yields and reducing labour demands without sacrificing the high pyrethrins’ content typical for Kenyan pyrethrum. Model-oriented research on crop phenology, light interception, light use efficiency, biomass growth and partitioning and water use efficiency could shorten the duration and lower the costs of experiments in potential yield exploration when introducing pyrethrum among existing agricultural systems. Strong campaigns against synthetic insecticides that pollute the environment are required in order to increase pyrethrum demand, and thus production and use.

Keywords: Pyrethrum; Ecological conditions; Agronomic practice; Research priority; West Kenya

1. Introduction

Pyrethrum (Chrysanthemum cinerariaefolium) is a small perennial plant cultivated for extraction of pyrethrins from the dried flower achenes. Pyrethrins are a group of six active chemical ingredients of acids and alcohols used in the manufacture of insec- ticides (Chandler, 1951; Head, 1966, 1969). The use of pyrethrum flowers for insecticidal purposes origi- nated in Persia. Chrysanthemum coccineum was the

* Corresponding author. Fax: +32 (9) 264-4997.

first species to be used. It was introduced into Europe in the 19th century and into the United States about 1860. Later, C. cinerariaefolium, probably the cor- rect name being Tanacetum cinerariifolium (Purse- glove, 1982) was found to be more effective and became the main source of pyrethrum. Originally, dried capitula were powdered for use, but replaced by kerosene extracts around 1920.

The use of pyrethrum was much extended in the 1930’s and assumed great importance during the second world war when it was used in mosquito repellent cream and ointment against scabies. It was

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308 f? Wandahwa et al./Industrial Crops and Products 5 (1996) 307-322

found to be effective against flies, fleas, lice and mosquitoes. It was also used to protect food and other produce. At present, it is used in livestock sprays, in fog generators to protect warehouses and in mosquito sprays and coils for burning. Pyrethrum solutions are used for dipping dried fish and meat against beetle infection with Dermestes species and blow flies, Cdiphoru species (Purseglove, 1982).

Despite the post war development of DDT and other chlorinated hydro-carbon and organo- phosphorus insecticides, pyrethrum has maintained a superior position as a natural insecticide. It is effective against a wide range of insects with lit- tle development of resistant strains. It has a rapid paralytic action or knock-down effect. It is low in toxicity to mammals and other warm blooded ani- mals and free from taint. It is non-inflammable and leaves no oily residue (Elliot et al., 1969; Purseglove, 1982).

For these reasons, it is particularly valuable for use in the home and where there are foodstuffs. With the use of synergists such as sesame oil, piperonyl butoxide and others, the cost of application is re- duced. The synergists are not insecticidally active, but have the properties of enhancing the toxicity of pyrethrins and thus reduce the amount that is needed to achieve a given level of insecticidal activ- ity. Apart from its use as an insecticide, pyrethrum mart, the flower grist that remains after extraction of pyrethrins, is used as an animal feed. This animal feed is marketed in Kenya under the name ‘Pymac’ and has the same nutritive value as wheat bran or pollard (Kayongo-Male and Abate, 1989; Mathur et al., 1961). This paper discusses the cultivation of pyrethrum in West Kenya and identifies areas of interest that require further research in order to im- prove farming conditions and increase yields among small scale farmers who are the majority cultivating this crop.

2. Origin and distribution

Chrysanthemum cinerariaefolium occurs in the wild on the Dalmatian coast of former Yugoslavia. It was introduced into Japan in 1881, which be- came the principal producer between the first and second world war (Purseglove, 1982). In the early 1920’s, it was planted in Switzerland and France.

Seeds from Switzerland and Japan were grown in England at Rothamsted Experimental Station from 1924 onwards. The station supplied seeds of the Harpenden strain to Kenya in 1929. In the same year, seeds were obtained from Dalmatia by the first farmer to grow pyrethrum commercially in Kenya. The second world war completely stopped supplies of pyrethrum from Japan leaving Kenya the world’s largest producer from 1945 till today. With increased demand during the war, production was extended to the highlands of Tanzania and Kigezi in southwest- em Uganda.

Pyrethrum has been tried in many countries in- cluding Rwanda, Ecuador, India, Zaire, Papua New Guinea, Nepal, China and Brazil (Ministry of Agri- culture, 1992). At present, the world’s second largest producer is Australia where it is grown intensively in the southern State of Tasmania. This fully mecha- nized production system in Tasmania was developed by CIG Pyrethrum, part of the world-wide multina- tional company BOC Gases Limited.

The pyrethrum industry in Australia was started when in the 1970’s a special pest control product ‘Pestigas’ based on synergised pyrethrins was devel- oped. Around the same time, the University of Tas- mania commenced a pyrethrum breeding program with genetic material from India. By 1980, several high yielding cultivars that produce one single flush of flowers and are suitable for mechanical harvesting had been produced.

Further trials by CIG Pyrethrum allowed it to develop a fully mechanized, commercial production system, the first of its kind in the world. In 1986, the area planted was increased and at present CIG Pyrethrum contracts 85 farmers in northwest Tasma- nia, the Coal River Valley and the Derwent River Valley to grow pyrethrum on 1200 ha. Production has increased from 300 tons of flowers in 1989 to 2500 in 1993 giving CIG Pyrethrum a 10 to 20% share of the world market (CIG Pyrethrum, 1995).

3. EcologlcaI conditions

3. I. Climatic conditions

In Kenya, pyrethrum grows well in high altitude areas between 1500 and 3000 m above sea level. Fig. 1 shows the highlands between latitudes l”3O’N

I? Wmdahwa et al./Industrial Crops and Products 5 (1996) 307-322 309

WESTPOKOT ’

f NANLX! I’--

: :’ I”

rd’

NAROK

\ l

MERU

w - - - district bolndory

* moior towns

I I I 1 0 25 50 xx) km

Fig. 1. Location of pyrethrum producing districts in West Kenya.

and 2“s and longitudes 34”30’ and 38”30’E compris- ing sixteen administrative districts (approximately 97,300 km*) that grow pyrethrum. Here, lack of extreme climatic variation experienced in temperate regions results in longer periods (between 8 and 9 months) of flower flush and picking (Muturi et al., 1969). Regions that have annual rainfall between 1000 and 1400 mm are very suitable for cultivation. Amounts greater than 1400 mm increase root rot and bud disease incidence (Parlevliet, 1970). In the Kisii highlands (west of Narok and Kericho districts) where annual rainfall is more than 1600 mm, and in regions with less than 1000 mm (as in parts of Nyandarua district), pyrethrum grows relatively well. Rainfall in Kisii is well spread throughout the year,

while the highlands of Nyandarua district experience misty conditions that reduce evapotranspiration. A dry period of at least 2 months rejuvenates plants. However, more than 4 months of dryness result in low yields (Acland, 1971).

The optimum temperature for maximum photo- synthesis lies between 15 and 20°C and chilling is required to initiate flowering (FAO, 1978). A tem- perature below 17°C for a period of six weeks is required to initiate flowering (Glover, 1955; Roes& 1976). Roest (1976) conducted experiments on the effect of nighttime, daytime and average temper- ature on the flowering of pyrethrum. He found that alternate low (under 13°C) nighttime and warm (15-20°C) daytime temperatures result in increased

310 Ff Wandahwa et al. /Industrial Crops and Products 5 (1996) 307-322

flower production. Average temperatures above 21°C inhibit flowering altogether. Temperature has a great effect on pyrethrins’ content of the flower as demon- strated by Kroll (1964) throughout Kenya. Regions with many cold misty and frosty months experience poor yields due to plant physiological damage, lack of warmth for vigorous growth and increased bud disease incidences.

3.2. Soil and landscape conditions

Pyrethrum grows well on fertile, deep and well drained soils. Loamy soils derived from volcanic rocks that are found in the central highlands of Kenya are most suitable. They are capable of holding high amounts of water and have good soil structure that ensures good water infiltration. The crop stays in the field for 3 years. Within this period, there is repeated weeding and trampling of the soil. Unless the soil has good structure, it breaks down quickly followed by erosion (Acland, 197 1).

Parts of Nyandarua and Narok districts are prone to waterlogging. It is recommended @roll, 1963) that the crop be planted on ridges because it does not tolerate waterlogged conditions. Ridging also cre- ates better aeration and the soil may be subjected more intensely to the warming rays of the sun thus promoting growth in young plants. Mulching is rec- ommended on soils that do not retain high amounts of water. Mulching in cold areas however, decreases yields in the first year probably due to cold top soil that causes poor development of young plants.

It can grow on soils that are gravelly, slightly alkaline, slightly saline or calcareous @roll, 1963). Where these soils are present in Kenya, they would probably be excluded from cultivation on the ba- sis of prevailing climatic conditions (Wandahwa and Van Ranst, 1996). Shallow soils (approximately 40 cm deep) found in the undulating to hilly landscape of Uasin Gishu district are utilized due to adequate rainfall (> 1000 mm) and the shallow rooting sys- tem of the crop. Most of the roots are found within the top 30 cm (Acland, 1971), while reported maxi- mum rooting depth is 50 cm (Jaetzold and Schmidt, 1982/83).

Experience in Kenya has shown that many small- scale farmers grow pyrethrum on land with a variety of physiographic units and at different slope levels.

Suitable areas should be considered in terms of how slope affects soil erosion and land preparation meth- ods. The crop gives little protection to the soil due to poor shading of the ground (Wielemaker and Boxem, 1982). This exposes the soil to direct rain drops and a variety of thriving weeds (Ngugi et al., 1989). Thriving weeds require frequent weeding that in turn causes soil pulverization and occasional trampling that reduces infiltration of water. Pyrethrum fields are therefore prone to soil erosion. Sloping land should be terraced or planted along contour lines.

Regarding soil reaction, available information is not conclusive. Soil analysis from farmers’ fields and the Pyrethrum Board of Kenya nursery fields show that the crop grows on soils that greatly vary in their pH values. In Molo, a region that produces high yields, the soils range in pH from 4.4 to 6.3, while in Meru, a region with very low yields, soil pH range between 4.0 and 6.3 (Pyrethrum Board of Kenya, 1990a, 1991a,b). In India, it is reported to have been grown on soils with pH values between 3.0 and 5.1 (Raghavan Nair, 1955). Weiss (1966) reports soil acidity tolerance between pH values of 5.3 and 6.0, while Jaetzold and Schmidt (1982/83) report values between 5.6 and 7.5. The Pyrethrum Board of Kenya (1992) recommends soil pH values above 5.6. Perhaps the suitable soil pH should be evaluated in relation to how it affects availability of nutrients to the crop.

Results of early experiments conducted by Kroll (1962, 1963) on the effect of calcium, magnesium, sulphur, molybdenum, zinc and copper on the pro- duction of pyrethrum were either not conclusive or showed that the crop does not respond to application of these elements. The Pyrethrum Board of Kenya (1992) recommends soils that have 2-10, l-3, 0.2- 1.0, 0.2-2.0 and l-2 cmol(+) kg-’ soil of Ca, Mg, K, Na and Mn, respectively; 24% organic carbon; 0.2-0.4% available N and 2&80 ppm of available P.

4. Management

4.1. Field establishment

Preparation of land to grow pyrethrum is aimed at eradicating perennial weeds. If the weeds are still in the field by the time the crop is planted, they can not be removed without destroying the crop (Acland,

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1971). On large scale farms, primary tillage is done using a mouldboard plough or disc plough mounted on a tractor. Secondary tillage is done using disc harrows twice or more on virgin land and once on fallow land. On small scale farms, either a pair of oxen (draught animals) or a hand tool (hoe or forked jembe) is used. A pair of oxen requires ploughing and repeating till a fine tilth is obtained. A hoe is used to break the soil and a forked jembe used once to make tbe tilth smooth. Land preparation should be done when the soil is not too wet or too dry.

The National Pyrethrum Research Station at Molo, a branch of the Pyrethrum Board of Kenya is responsible for producing planting material. Pyrethrum is planted from seeds as in varieties, or from splits as in clones. Research is aimed at producing varieties and clones that are high yield- ing in flowers and pyrethrins content, and which are resistant to diseases and pests. Clones are pro- duced through recurrent selection from the popula- tion. Improvement is achieved by concentrating on favourable characteristics (genes or alleles). Varieties are produced through hybridization of two, three or more selected mother clones. Mother clones are mul- tiplied through tissue culture.

Farmers buy seeds from the Pyrethrum Board of Kenya office in Nakuru district, or purchase seedlings or splits from regional Pyrethrum Board of Kenya nurseries. Seeds are planted in raised seed- beds that measure 1.5 m wide and extend to any length. Phosphorus is applied prior to planting at the rate of 38 kg of P ha-’ and mixed with the top soil. Seeds are sown in furrows of 1.5 cm deep and 15 cm apart at a rate of approximately 100 seeds for 25 cm length. The seed-bed is covered by a thin layer of grass and water is applied.

After 10 to 15 days, seeds germinate and the covering grass is reduced gradually to harden the shoots. Sometimes germination is quite poor due to the presence of unfertilized and non-viable seeds. Germinated seedlings are top dressed with 52 kg ha-’ of N. Fungi and thrips are prevented from at- tacking seedlings by spraying with 20 ml of Dithane M45 in 20 1 of water and 30 ml of Metasystox in 20 1 of water. Weeds are pulled out by hand. Four months after planting, seedlings are ready for transplanting.

Multiplication of selected clones to produce splits is done in holes dug 15 cm deep at a spacing of

30 cm between rows and 15 cm within rows. Plants used for vegetative propagation are dug out using a forked jembe to avoid damaging the roots. Roots are trimmed to 10-15 cm long and flowering stems are cut off. The plants are divided into splits leaving a good proportion of the root system on each split. The number of splits produced per mother plant depends on the number of tillers the plant has (Kroll, 1948). Fungicides and nematicide are applied when necessary. The splits are planted vertically in the dug holes. Weeds are controlled by weeding regularly. Three to four months later the plants are ready to provide splits for distribution to farmers.

Pyrethrum is transplanted at the beginning of the ‘long rains’ in March or April. Holes are dug 15 cm deep at a spacing of 60 cm between rows and 30 cm within rows and 38 kg ha-’ of phosphorus (basal P) applied. Roots and stems of splits or seedlings are trimmed and treated with fungicides and nematicide where necessary. They are planted vertically in the dug holes. The soil is put firmly around them. Be- tween 5 and 10% of the plants may die. Gaping, a process of replacing the dead plants should be done without delay using large splits or seedlings in order to maintain proper plant population and allow re-fills to catch up with the rest of the plants.

4.2. Fertilizer application and response

4.2. I. Phosphorus

The first experiments conducted on pyrethrum in Kenya between 1945 and 1947 included the effect of mulch, lime and phosphates. As superphosphate was in rather short supply during the years imme- diately after the second world war, a mixture of 4.5 units of Uganda rock-phosphate and 1 unit of triple superphosphate was used. The results were rather disappointing. Only the water soluble superphos- phate gave an immediate response, which in most cases was short-lived and sometimes resulted in di- minished yields in the following years (Kroll, 1962, 1963). Application of lime produced no response in most cases, while mulch acted in different ways ac- cording to soil type, air temperature and rainfall at various altitude levels.

Although these experiments were conducted over a fairly wide range of soils, it was considered de- sirable to increase the scale of subsequent trials.

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Work on phosphorus in particular was intensified from 1950 onwards. After a few seasons, it became obvious that the more leached red soils of high al- titude areas (above 2400 m) gave remarkable yield responses when between 158 and 224 kg ha-’ of triple superphosphate (TSP, 43% PzOs) was applied. The phosphate was applied in the hole during plant- ing and increased initial take, plant vigour as well as eventual flower yields @roll, 1962; Weiss, 1966). Top-dressing after planting or in the second or third season never had any effect. High TSP (448 kg ha-‘) application had no effect on flower yield whereas phosphorus application failed to increase the con- centration of pyrethrins in the flowers (Kroll, 1962; Parlevliet et al., 1968).

Reports on pyrethrum response to P application are conflicting. Studies in Kenya have shown positive yield responses @roll, 1962; Wanjala, 1991a), or no response at all (Mwakha, 1979). Similarly, 30% yield increase was obtained in Banglor (Rajeswara Rao et al., 1983) and Kodaikanal (Kumar et al., 1982), and no response in other experiments in India (Hussain and Ram, 1976; Rajeswara Rao and Singh, 1982). Ngugi and Ikahu (1989) showed that flower yield of clone 01641219 increased by 5% in two consecutive seasons when P was applied, whereas clone 4331 showed no response in either season. Clone 4331 did not respond to P application at Molo (Mwakha, 1979) and even produced 5% lower yield when P was increased from 97.5 to 195 kg ha-’ (Parlevliet et al., 1968).

The trend reported in Kenya concerning the re- sponse of clone 4331 to P application is similar to that reported for clone CIG3 in Tasmania, Aus- tralia (Salardini et al., 1994a). Like in Kenya, P application in Tasmania failed to increase the con- centration of pyrethrins in the flowers. In Kenya, the concentration of pyrethrins was influenced by clone differences, weather conditions and water supply (Wanjala, 1991a).

The differences in response of pyrethrum to P could be explained by differences in uptake effi- ciency among clones and between young and es- tablished plants. In the preparation of splits, plants are divided into four or more splits, and roots and shoots are trimmed. At planting, active root volume is small, and plant vigour is significantly reduced by splitting and the shock of transplanting. At this

stage, the splits need large supplies of P to fulfil their needs. In subsequent years, the roots of established plants may be able to obtain enough P from the soil. This, however, does not explain the reduction in yields which requires further investigation. Until more is known about the P nutrition of pyrethrum, it is recommended that, to minimize the risk of yield reduction, not more than 50 kg ha-’ of P and no side- dressed P should be applied (Salardini et al., 1994a).

4.2.2. Nitrogen Early experiments conducted in Kenya showed

that N application to pyrethrum either had negative or no response (Collings-Wells, 1962; Kroll, 1953, 1962, 1963; Omerod, 1951). The significant response in the first and second seasons reported by Mwakha (1979) was a result of clone improvement. He ob- served that towards the end of the season, plants that did not receive N application had a characteristic yellowing of mature leaves and stalk terminals.

In Kashmir India, N application increased tiller development and flower yields (Hussain and Ram, 1976). Ngugi and Ikahu (1989) observed differ- ences in the way clones respond to N applica- tion. Clone 064/219 significantly increased in flower yields whereas clone 433 1 did not. Nitrogen applica- tion did not increase pyrethrins concentration in the flowers. Wanjala (1991a) recommends 52 kg ha-’ N top-dressed three months after transplanting in the first season, and repeated after cutting back in the following seasons (Pyrethrum Board of Kenya, 199Ob).

4.2.3. Potassium Information on yield response of pyrethrum to K

application is limited. In Kenya, there has been no flower yield response to K application (Kroll, 1962, 1963; Parlevliet et al., 1968). In India, the response to K application has either been very small (under 5%) (Hussain and Ram, 1976; Rajeswara Rao et al., 1983) or absent (Rajeswara Rao and Singh, 1982). The amounts applied were approximately 110 kg ha-’ of K. Research in Tasmania has shown that pyrethrum (clone CIG3) requires about 40 kg ha-’ yr-’ of K, and does not respond to K applied on soils with more than 75 mg K per kg of soil (Salardini et al., 1994b). It is therefore recommended to apply 200 kg ha-’ of K at planting and 50 kg ha-i during

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the following seasons on soils with less than 75 mg K kg-’ of soil. Most soils in Kenya have sufficient K and its application therefore may not be required.

4.3. Crop protection

4.3-l. Weed control Weeds found in pyrethrum fields vary from place

to place. Those common to both low and high alti- tude areas include: Digitaria scalarurn chiov (Couch grass); Gulinsogu puruifloru Cav (Gallant soldier); Amaranthus hybridus L. (Pig weed); Tugetes minutu L. (Mexican marigold); Eleusine indicu L. (Wild fin- ger millet); Bidens pilosu L. (Black jack); Duturu strumonium L. (Thorn apple); Cyperus rotundus L. (Nutgrass or Watergrass); Oxulis lutifoliu H.B.K. (Oxalis); Commelinu benghulensis L. (Wandering Jew); Portulucu oleruceu L. (Purslane) and Pen- nisetum clundestinum (Kikuyu grass). Those con- fined to high altitude areas include: Brussicu nu- pus L. (Rape); Stelluriu media L. (Chick weed); Spergulu urvensis L. (Spurrey); Gulium spurium L. (Cleavers or goose grass) and Chenopodium opuli- folium (Round leaved goosefoot).

The effective way to control weeds in pyrethrum fields is by hand weeding (Kroll, 1948; Mwakha, 1974; Ngugi et al., 1989; Wanjala, 1989). A small forked jembe that does not damage roots is used for weeding and putting the soil around the plants to encourage tillering (Acland, 1971). This should be done once every month (4 weeks) (Mwakha, 1974). Research on the use of herbicides is continuing and preliminary results indicate that herbicides are not effective against Digituriu sculurum, Cyperus rotun- dus, Commelinu benghalensis and Oxulis lutifoliu that have to be removed by hand (Ngugi et al., 1989; Wanjala, 1989).

4.3.2. Disease control True bud and false bud diseases affect pyrethrum.

Although first reported in Kenya in 1946, available information on what really causes true bud disease is quite confusing. Reports (Nattrass, 1952, 1953, 1961 quoted by Robinson, 1963; Pyrethrum Board of Kenya, 1992) indicate that the disease is caused by fungi Rumuluriu bellunensis and Alternariu tenuis, a bacteria of Aschochytu spp. and a foliar nema- tode Aphelenchoides ritzemabosi (Schwartz) Steiner.

Robinson (1963) refers to Alternuriu tenuis as a fungus of doubtful pathogenicity while Aschochytu spp. and Rumuluriu bellunensis are reported to cause Aschochyta disease and true bud disease, respec- tively. According to Bullock (1961), Aphelenchoides ritzemubosi is a leaf eelworm that causes leaf chloro- sis and necrosis but which has little economic impor- tance.

The fungus R. bellunensis infects flower buds through the bracts and later invades the flower stalk. The buds start to dry and turn brown or purple-grey, the flower stalk withers as far as 2.5 cm below the bud and the dead bracts, florets and rays become confined to one side and looks like a ‘hanged man’ (Robinson, 1963). False bud disease is a physiolog- ical disorder that is associated with the genetic con- stitution of individual plants or clones and is caused by environmental conditions. Though it affects buds of all sizes, those between 1 and 2 mm diameter are most affected but can not be seen as they are hidden within the foliage. The small dead buds are termed ‘pin heads’. The characteristic symptom of false bud disease is the rapid death of several cen- timeters of stem below the dead bud followed by bending of the dead stem to produce a ‘shepherds’ crook’ (Robinson, 1963).

Root rot or wilting disease is caused by fungi Fusurium gruminurium, Sclerotiniu minor (which occurs quite often), Sclerotiniu sclerotiorum and a nematode Prutylenchus spp (Pyrethrum Board of Kenya, 1992). Wounds caused through splitting and weeding, and the piercing of nematodes act as entry points for the fungi. The affected plants slowly wilt and die. In some cases partial recovery of the plant may occur. Root rot is local in distribution and is associated with poor soil drainage (Robinson, 1963), sites where huts were built and fertile forest soils (Acland, 1971).

True bud disease and root rot are controlled through spraying with a fungicide Benlate at the rate of 0.5 kg ha-’ every two weeks. Preventive measures include: burning the cut plants at the end of the season, planting disease free material dipped in fungicides to protect wounds caused by splitting, applying nematicide in areas where nematodes are prevalent and practising crop rotation to keep down disease incidence. A more practical solution is to breed disease-resistant varieties.

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4.3.3. Pest control In Kenya, two different types of thrips are known

to cause economic problems at different levels of production in the pyrethrum industry. Thrips nigmpi- Zosus Uzel (leaf thrips) poses problems to pyrethrin production. Thrips tubaci Lind (flower thrips) affects seed production. Both differ in their predatory habits. Thrips nigropilosus Uzel which was first discovered in Kenya in 1957 scrapes the leaf epidermis, thus reducing chlorophyll content, and feeds on the cell contents. This causes leaf desiccation and foliar dam- age that appear as silvery patches and later become necrotic. The nymphs spend the first and second stages of their lives on leaves while the third and final stages are spend in the soil. Thrips tubuci Lind, first recorded in Kenya in 1937, lives exclusively in the flower where it attacks petals and florets making them brown (Bullock, 1961).

Few thrips can be tolerated by the pyrethrum plant before significant yield losses (in relation to costs of control) occur. As the loss can be very large (43%) in the dry season, farmers are advised to spray as soon as the leaf thrip is present on the foliage (Smith and Hanson, 1991). Spraying with Roger (dimethoate 40%) at the rate of 0.5 1 in 400 1 of water will control the d-nips. Preventive measures include removal of weeds like Galinsoga parvijlora and Bidens pilosa that are alternative hosts of leaf thrips.

The Red spider mite (Tetranychus Meni) is a pest of economic importance in areas with a marked dry season. Its numbers have been known to increase when DDT or dieldrin is used against thrips (Acland, 1971). In Kenya, the pest is found in all pyrethrum growing areas and can be controlled by spraying di- methoate 40% and thioden 35% at the rate of 11 ha-‘.

Earlier reports (Bullock, 1961; Robinson, 1963) indicated that pyrethrum was either tolerant to root knot nematodes (Meloidogyne hapla, Chitwood) or that the effects of the species did not appear dam- aging to the plants. It was later found however, that the nematodes can be quite a menace during a dry season (Acland, 1971). They attack pyrethrum roots and form knots. The plants appear healthy during the rainy season producing flowers as usual but show symptoms of attack during a dry season.

Furadan (Carbofuran) at the rate of 1 g per plant- ing hole should be applied during planting. Mocap 10G and Nemacur can be sprayed in the fields at the

rate of 2.0-4.0 g per plant and 0.5 g per plant, re- spectively. These applications will control any other soil insects (Cutworms, Diptera and Coleoptera lar- vae) that may pose hazards to the plants. Preven- tive measures include: planting disease free material, breeding resistant varieties and use of a cereal (e.g., wheat) in the rotation. Wheat is a poor host of root knot nematodes (Johnson, 1985).

4.4. Flower harvesting and handling

In Kenya, pyrethrum produces flowers continu- ously for a period of eight to nine months. Therefore harvesting is done by hand. During this period, all stages of flower development are present. Eight dis- tinct stages of development are shown in Table 1 (Head, 1966). The concentration of pyrethrins in the ‘flower’ increases from bud (stage 1) to a maximum when 3 to 4 rows of ray florets are open (between stage 4 and 5), and then reduces gradually as the florets mature. The dry weight of the flower head in- creases from bud stage to reach maximum at the late overblown stage 7. Research in harvesting pyrethrum flowers focuses on high yield of pyrethrins content (w/w) (Bhat and Menary, 1984; Head, 1963, 1966; Kroll, 1948; Parlevliet, 1970). Most clones have high pyrethrins’ content between stages 5 and 7 (Ikahu and Ngugi, 1989).

The first harvest should take place when the first flowers have all disc florets open (stage 5), approx- imately 21 days after the buds are fully developed. Subsequent harvests should be done every two weeks (14 days) and should include all flowers in stage 5 and above. In this way, flowers previously in stage 2, 3 and 4 are harvested while still having high pyrethrins’ content. Precautions should be taken not to pick flowers when they are wet and not to include part of the flower stalk among the flower heads as they reduce the pyrethrins’ content.

After harvesting, flowers should be dried imme- diately to avoid fermentation and loss of pyrethrins. Drying using machines has been tried in Kenya (Acland, 1971; Mumo, 1961) but has not been very successful (Pyrethrum Board of Kenya, 1992). Therefore farmers dry their flowers in the sun on wire mesh trays raised 0.6 to 1 m above the ground. Flowers are spread in a thin layer (about 4 cm) to allow air circulation and stirred at least 3 times a day.

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Table 1 Flower development stages and number of days to each stage (source: Head, 1966)

Stage of Description Approximate time for development development (days)

1 Well developed closed buds 0 2 Ray florets vertical 12 3 Ray florets horizontal, first row of florets open 16 4 Approximately 3 rows of disc florets open 19 5 All disc florets open, and fully mature 21 6 Early overblown condition, disc florets’ color diminishing but ray

florets still intact 31 7 Late overblown condition, little color remaining in ray florets but still intact,

ray florets dried out 43 8 Disc florets fallen, stems dry a centimeter below the head, suitable for seed collection 60

At night or during the rain, they are covered or put indoors. They are dry (lO-12% w/w moisture) when 4 out 5 flower heads smash easily when squeezed be- tween thumb and fore-finger. Dry flowers are packed in sisal bags to about 30 kg that are well labelled for transportation to the factory.

Dried flowers are sold to the Pyrethrum Board of Kenya in Nakuru where processing takes place. The Board has a network of buying centers within the growing regions. The centers consist of cooperative unions with 100 or more members receiving flowers from smaller societies to deliver to the factory, asso- ciations of 20 to 30 members that deliver their flowers as a group, or individual farmers who deliver them- selves to the factory or through the pyrethrum field officers. Payments are delivered to the cooperatives, associations, field officers or to the individual farmer.

5. Management constraints

5.1. L49wjoweryielak

Farmers’ yields are not well documented. To- tal production of dried flowers is recorded by the Pyrethrum Board of Kenya (PBK) which buys all the flowers. The land area under production is not well documented as some farmers are not registered and sell their flowers through registered ones. Flower delivery increased from 7537.8 tonnes in 1988/89 season to 9640.6 tonnes in half of 1992193 sea- son. The Ministry of Agriculture reports dried flower yields and attempts to estimate the land area under production using their extension service officers.

While utilizing information from the District An- nual Reports of the Ministry of Agriculture (1987- 1991), the Pyrethrum Board of Kenya papers, and the agronomy section of Pyrethrum Board of Kenya, an attempt was made to calculate the average dis- trict dried flower yields of the farmers (Table 2). There was a steady increase in yields from 1987 to 1991, probably due to improving management practices. Despite the variations, yields show a gen- eral decreasing trend from Nakuru to Embu district. Matching Tables 3 and 4 adapted to climatic and soil conditions with the respective climate and soil con- ditions where pyrethrum is grown (Table 5) in West Kenya, revealed that Embu and Murang’a districts are less favourable for pyrethrum cultivation. As a result, average annual yields are low. In 1960, the average annual yield was about 440 kg ha-’ yr-’ of dried flowers. This amount fell as the growing of flowers changed hands from experienced large-scale farmers to inexperienced small-scale holders and spread from more favourable areas in Nakuru district to less favourable areas in Murang’a and Embu dis- tricts. By the end of 1960s the average had fallen to 280 kg ha-’ yr-’ (Acland, 1971). In 1960, farmers practising good crop husbandry obtained about 1350 kg ha-’ yr-’ of dried flowers. Similar yields are still realized today under experimental conditions, with those common between 1500 and 2000 kg ha-’ yr-‘. Yields above 2500 kg ha-’ yr-’ are rare and have been reported (Ngugi and Ikahu, 1989) at Molo Research Station for clone 4331, the highest being 4681.8 kg ha-’ yr-’ with 1.5% (w/w) pyrethrins’ content. There is need to restrict cultivation to areas

316 F! Wandahwa et al./Industrial Crups and Products 5 (19%) 307-322

Table 2 District pyrethrum yields (kg ha-‘) from 1987 to 1991 in 15 districts in West Kenya

District Year

1987

NaklUll 740 Kericho 308 Uasin Gishu 399 Baringo 278 Nyandarua 334 Marakwet 185 Narok 184 West Pokot 160 Kiambu 396 Laikipia 152 Nyeri 240 Nandi 117 Meru 239 Murang’a 80 Embu - Average 272

a CV, coefficient of variation.

1988 1989 1990 1991

689 507 541 663 391 457 644 715 436 520 605 496 244 242 665 624 373 352 283 423 181 178 593 516 152 256 547 489 210 300 360 467 316 250 252 255 107 293 542 354 200 253 237 256

- 333 400 287 248 238 242

- 38 - - 18 22 60 36

277 280 421 424

Average CV a (%)

628 15.9 503 34.1 491 16.2 411 52.2 353 14.6 331 62.4 326 55.4 299 40.6 294 21.6 290 59.9 237 52.3 283 8.1 251 9.3

59 51.2 34 56.1

319 -

Table 3 Climatic requirements for pyrethrum cultivation

Climatic Decreasing favourable conditions from 1 (very good) to 5 (unsuitable) characteristics

1 2 3 4 5

Mean annual rainfall (mm) a 1100-1200 1200-1400 1400-1600 >I600 -

1000-1100 95&1000 900-950 C900 LDS b (months) l-2 3 4-6 7 >7

- <l -

Mean nighttime temperature’ (“c) <ll 11-13 13-15 15-17 >17 Mean daytime temperature d (“c) 15-20 20-22.5 22.5-25 >25

- 13-15 cl3 Average daily temperature e (“c) 12-15 15-17 17-19 19-21 r21

- 10-12 7-10 <7

B Increasing rainfall increases disease incidence while less is inadequate. b Length of a dry season of 1 or 2 months rejuvenates plants, continuous rams are not very favourable and the crop fails in areas with more than 7 months of dryness. c Lower temperatures encourage bud formation. d Temperatures affect flower development. e Temperatures used in absence of nighttime or daytime temperatures.

with favourable climate where great potential to in- crease yields obtained by farmers and those obtained under research conditions exists.

5.2. Fluctuating world market and producer prices

pyrethrins are refined and put into containers for ex- port. More than 95% of the pyrethrins are exported, the rest is utilized locally to make insecticides. From what is exported, 65% is sold to the USA. The rest is sold to Europe, Asia, South America, the Caribbean, Middle East and some African countries.

Pyrethrins are extracted from flowers at the Unlike tea and coffee, the world market price Pyrethrum Board factory in Nakuru. Extracted for pyrethrum is not determined in auctions and is

F! Wana’ahwa et al./Industrial Crops and Products 5 (19%) 307-322 317

Table 4 Soil and landform requirements for pyrethrum cultivation

Land-use requirements/ Decreasing favourable conditions from 1 (very good) to 5 (unsuitable) characteristics

1 2 3 4 5

Erosion hazard

s1ope.a (%) <8 cl6 <25 <30 >30

Wetness b

Flooding c FO Fl Drainage d

F2,F3 WD SED ED MD I,P,VP

Rooting conditions

Texture and structure e C<6Os to L C>6Os, SCL SL, C<6Ov C>6Ov, LfS, LS SiCm, Cm, S, fS, CS Coarse fragments (%) <5 5-15 15-35 35-55 >55 Soil depth (cm) >90 60-40 40-20 (20 CaCOs (%) t12 12-24 24-35 35-50 250

Fertilig status Apparent CEC (cmol (+) kg-’ clay) >24 24-16 <16 (-) <16 (+) Sum of basic cations (cmol (+) kg-’ soil) >3.2 3.2-2.4 2.4-1.6 <1.6 pH water (1: 2.5) 6.0-5.6 5.6-5.2 5.2-4.8 14.8

6.0-6.4 6.4-6.8 6.8-7.5 >7.5

Organic carbon (%) >2.4 2.4-1.5 1.5-0.8 to.8

Salinity and alkalinity hazard ECe f (dS/m) c2.0 2.0-4.0 4.0-8.0 8-15 215 ESPs (%) ~6.0 6.0-10 10-15 15-40 >40

a Increasing slope increases erosion hazard. b Water logging is not tolerated. ’ FO, Fl , F2, and F3 indicate none, occasional, seasonal and permanent excess surface water, respectively. d VP, very poorly drained; P, poorly drained; I, imperfectly drained; MD, moderately drained, ED, excessively drained, SED, somewhat excessively drained; WD well drained. eCm, massive clay; SiCm, massive silty clay; CAOv, fine clay, vertical structure; CAOs, fine clay, blocky structure; C<6Ov, clay, vertical structure; 0s to L refers to: clay, blocky structure; silty clay, blocky structure; silty clay loam; clay loam; silt loam; sandy clay; and loam; SCL, sandy clay loam; SL, sandy loam; LfS, loamy fine sand; LS, loamy sand, S, sand; fS, fine sand; cS, coarse sand. f ECe, electrical conductivity of the saturation extract. s ESP, exchangeable sodium percentage.

less transparent. Negotiations with known customers of the Pyrethrum Board are done through telephone or telex. Competition from cheap synthetic products affect both the world market and producer prices. In 1982/83 season, total flower production was about 19,000 tonnes. By the end of 1983, there was a stock pile of 19,000 tonnes of pyrethrins’ extract in Kenya due to poor world market prices. Farmers were not paid in time for the flowers they delivered to the factory, the delay lasting for more than 18 months in some cases. Most farmers uprooted the crop and annual production fell to about 3000 tonnes of dried flowers in 1983/84, 1984/85 and 1985/86 seasons. Improvement of world market prices in 1987 and depreciation of the Kenya shilling in 1989 led to

increased producer prices (Table 6). By 1990/91 season, annual production had increased to 10,000 tonnes of dried flowers (Ministry of Agriculture, 1992).

Producer prices are worked out by the Pyrethrum Board using information generated from monthly flower deliveries, annual production estimates, world market price indications and trends. Using a trad- ing account through costing of processing, transport, personnel, chemicals, etc. an interim (before end of financial year) price is worked out on the ba- sis of pyrethrins’ concentrations in the flowers. In 1990/91 season, interim producer price was Ksh 2500 kg-’ pyrethrins (US$ 1 = Ksh 30.026, 31 March 1991). One tonne of dried flowers containing

318 I? Wandahwa et al. /Industrial Crops and Products 5 (19%) 307-322

Table 5 Dominant soil units and climatic conditions where pyrethrum is grown in 15 districts in West Kenya

District Soil units MABa MANTb MADT c LDS d (FAO-UNESCO, 1974) (mm) (“c) (“C) (months)

N~~uN mollic Andosols ando-luvic Phaeozems 950-1400 tll-15 15-20 l-6

Kericho mollic Nitisols ando-luvic Phaeozems 1200-1400 11-15 15-20 l-4

Uasin Gishu humic Nitisols 1100-1400 11-13 15-20 l-4 Baring0 nito-chromic Luvisols 12c0-1400 11-13 15-20 14 Nyandarua nito-chromic Luvisols

ando-luvic Phaeozems looo-1400 <ll-13 15-20 26 Keiyo trim-chromic Luvisols Marakwet humic Nitisols 1109-1200 11-15 15-20 3-t Narok ando-luvic Phaeozems

mollic Nitisols llcO-1600 tll-17 15-25 1-3 West Pokot humic Cambisols 1100-1200 13-15 15-20 3-4 Kiambu humic Nitisols 100&14QO 11-15 15-20 4-6 Laikipia n&o-chromic Luvisols 950-loo0 13-15 15-22.5 4-6 Nandi hmnic Nitisols 1200-1400 13-15 15-22.5 l-3 Meru humic Nitisols 950-1400 13-17 20-25 4-6 Nyeri humic Nitisols 950-1400 13-17 15-22.5 4-6 Murang’a humic Nitisols 950-1400 15-17 15-22.5 4-6 Embu humic Nitisols 900-1100 15-17 20-25 4-6

a Mean annual rainfall. b Mean annual nighttime temperature (“C). c Mean annual daytime temperature (“C). d Length of a dry season, defined as number of months rainfall is less than half of evapotranspiration.

1.0% of pyrethrins concentration was Ksh 25,000, while that containing 1.2% was Ksh 30,000.

Interim payments are made every month for flow- ers delivered the previous month. At the end of the season, a pool price is worked out and final pay- ments are made. The final payment is referred to as ‘bonus’. Better producer prices and increased flower production will lead to high income that can sus- tain a farmer throughout the year just like formal employment.

5.3. Research, finding and dissemination of information

Agronomic research is done by the Na- tional Pyrethrum and Horticulture Research Station (NPHRS) at Molo, a branch of Kenya Agricultural Research Institute (KARI) and the agronomy section of the Pyrethrum Board of Kenya (PBK). Breed- ing is exclusively done by the NPHRS. Table 7 shows a list of clones and varieties recommended by the NPHRS. Besides these, farmers grow a number

of local clones especially in Kisii (west of Narok and Kericho districts). Among them are Kenya, K7, Maranga, Gekoma, Nyamasibi, Nyankoba, C47, Ebiosi and Congo (Wanjala, 1991b). These clones are numerous and proper research cannot be done on all of them given the limited funds. Besides, there is lack of coordination in research between the PBK and KARL Each researcher deals with the clones he likes and lays down the experiment on the soil and environment he likes. The results are inconsistent and difficult to use.

Fertilizer trials are the dose-response type in which the fate of fertilizer nutrients applied is not part of the investigation. Measurements of nutrient contents in the various crop parts and in the soil are not done. Published nutrient concentration values in harvested product and crop residue are too general and not clone specific (Smaling et al., 1993). It is therefore difficult to establish the crucial relations between nutrient application and nutrient uptake and that between nutrient uptake and yield. No infor- mation is available on the fraction of the inorganic

f? Wundahwa et al. /Industrial Crops and Products 5 (19%) 307-322 319

Table 6 Table 7 Pyrethrum producer prices in Kenya and percent increase over the previous year from 1975 to 1990 (Source: Ministry of Agri- culture, 1992)

Year Price (Ksh a kg-’ pyrethrins)

Increase (%)

Recommended clones and varieties in Kenya, year of release, pyrethrin concentration and altitude above which they should be grown (Source: Pyrethrum Board of Kenya, 1990a; Pyrethrum Board of Kenya, 1992)

1975/76 392 1976/77 430 9.7 1977t78 516 20.0 19780’9 670 29.8 1979180 1000 49.8 1980/8 1 1150 15.0 1981/82 1150 0.0 1982/83 1150 0.0 1983/84 1150 0.0 1984/85 1150 0.0 1985/86 1250 8.7 1986187 1304 4.3 1987188 1650 26.5 1988/89 2030 23.0 1989190 2615 28.8

a30.026 Kenya shillings = LJS$ 1 on 31 March 1991.

Clones/varieties

Clones 4331 Sbl661107 Ma/700013 KG’0164 Ma/71/423 Kst751313 Kst7U43 L/72/26 Krl741443 Km41223 Km4tl22 MoL’Olll24

Varieties P4 K218 K235

nutrients applied that is taken up by the plant (recov- ery fraction) on different soils and environments in Kenya. No information is available on nutrient uti- lization efficiency by different clones for production of biomass with an economic value, There is need for research that will provide this information.

Pyrethrum continues to gain interest as a new in- dustrial crop among small scale farmers who would like to grow it. Crop yield simulation models are an important land evaluation tool used in making decisions on whether to or not to introduce new crops into existing agricultural systems. Such quan- titative models require specific crop parameters not available in the case of pyrethrum. So far, only a qualitative (descriptive in nature) land use as- sessment model in which the concept of land use and the associated crop requirements are formu- lated against a socio-economic background has been demonstrated (Wandahwa and Van Ranst, 1996). Model-oriented research on crop phenology, light in- terception, light use efficiency, biomass growth and partitioning and water use efficiency is required in order to shorten the duration and lower the costs of experiments in potential yield exploration when introducing pyrethrum among existing agricultural systems.

Research work should also cover mechanical har- vesting and drying which will reduce the high labour demand of the crop. The present clones which flower continuously for 8 to 9 months are difficult to har- vest with machines without spoiling the crop. There is need for a decision on whether clones that pro- duce flowers at once and which are therefore easy to mechanize should be developed (like in Tasma- nia) or whether those that flower for a long period and require manual labour should be retained. Re- search on high yielding and disease resistant vari- eties, pesticides and herbicides’ application should be intensified. The problem of clones with high dried flower yields having low pyrethrins’ concentration should be investigated and solved through genetic engineering.

Research funds are limited. The PBK allocates Ksh 400,000 to research annually. This amount is too limited and should be increased. However, farm- ers will only accept research funds to be increased if recommendations out of research findings are use- ful to them. Research information is disseminated through an exclusive journal, ‘The Pyrethrum Post’ published since 1948, and other publications of the

Year of Pyrethrins Altitude release concentration (%) (m)

1964 1.6 1800 1976 2.0 2200 1979 1.9 2200 1979 1.9 1700 1979 1.8 2200 1979 1.6 1700 1980 2.1 1700 1980 2.1 2200 1982 2.1 1700 1982 1.95 1700 1982 2.1 1700 1979 1.9 2200

1970 2.0 2100 1988 2.1 1700 1988 1.9 1700

320 I! Wandahwa et al./Industrial Crops and Products 5 (1996) 307-322

agronomy section of PBK. Once research in agron- omy is improved, the quality of information reported in these publications will also improve.

5.4. Credit and extension services

Farmers need credit to manage the high opera- tional costs at the start of the first season. When harvesting starts, they should be able to sustain pro- duction costs since they are paid every month for flowers delivered the previous month. The credit scheme currently operated by PBK does not cover everybody. It is given as farm inputs and lowers the farmers’ costs of production. For example in 1991/92 season, a 50 kg bag of triple superphosphate (TSP) was supplied to farmers in Kisii district at a cost of Ksh 415 instead of the commercial price of Ksh 426. Credit facilities are also provided for transportation of planting material to tbe farmer and dried flowers to the factory.

There exists conflict between the PBK exten- sion officers and those of the ministry of agricul- ture. Farmers are in the process left without the necessary advice. Frequent field days and seminars should be organized in order to reach farmers. Ex- tension service officers of the PBK need regular in-service courses to upgrade their knowledge on re- search information, data collection and record keep- ing. Pyrethrum is one of the crops with high labour requirements. Farmers should be well advised before engaging in production.

6. Conclusions

There was a steady increase in flower yields in West Kenya from 1987 to 1991, probably due to improving management practices resulting from in- creasing producer prices. Growing pyrethrum in less favourable climatic conditions results in low yields. There is need to restrict cultivation to areas with a favourable climate where potential to increase yields through good crop husbandry and better credit facil- ities exist. Natural pyrethrum products face compe- tition from cheap synthetic ones, despite their being harmful to mammals. Strong campaigns against the harmful cheap synthetic products and better market- ing strategies for pyrethrum could increase use and thus demand for safe pyrethrum products. Research

on high yielding varieties (high dry flower weight and pyrethrins concentration) that are resistant to diseases and pests and have low labour demands, is necessary for the pyrethrum industry in Kenya to succeed.

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