February 3-4th, 2014 Wad Medani, Sudan

Early Season Weed Management-Syngenta Perspective

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• A critical step in yield management commences early in the season with an

effective weed management programme.

• Research in Maize development and the realisation of its yield potential has

played a significant role in shifting the emphasis and focus in weed

Management strategies

• In other crops such as Wheat, weed competition is the greatest threat to yield

• Focus on Early Season Weed Management (ESWM)

Early Season Weed Management & Yield Management

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Yield Management

Irreversible yield losses

Yield maximization

“switching point”

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Maize can loose the war before it has even started

● With new research, researchers have shown that maize plants immediately goes into a “defensive stage” when weeds are sensed.

Yield loss due to weeds

Increased yield due to weed control.

CPWC: “Critical Period for Weed Control”

Critical window:

MoistureNutrients

EvaporationRoot developmentLight interception

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Optimal window for weed Management in maize

BEFORE

the switching point is reached

A maize plant’s theoretical yield potential is determined between the 1 – 5 leaf

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● Key Features

Strategy must have an economical as well as environmental

consideration

Weeds don’t have to be 100% controlled for the total season.

Important to take into consideration the Critical periods in weed

management

Weed types & Biology

Weed propagation (seeds vs vegetative), Seed Dormancy

Interference with crops & impact on yield and quality

Effect on herbicide strategy & choice of treatment

Application technique

Weed management strategy:

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ESWM- Breaking Cycle of Resistance

● ESWM

Increasing resistance development against two modes of action:

• ALS inhibitors i.e. Sulfonyl ureas,

• ACCase inhibitors i.e. `Fops`, `dims` & `dens` herbicides

Weed Resistance observed predominantly where chemical control has been based on post emergence chemistry

• Target Site Resistance

• Enhanced Metabolism Resistance

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• The most important weeds can be classified in three distinct groups which will

dictate the herbicides to recommend.

• These groups differ in their sensitivity towards herbicides and therefore need

different approaches when herbicides are recommended.

• Weeds also differ in their ability to germinate from different depths and their

period of germination which again dictates the choice of herbicide/s.

Biology and ecology of weeds

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Weed types

MONOCOTS DICOTS SEDGES

Usually grasses, but also include some weeds that appear to be broad leaved.

Usually germinates shallow (top few millimetres) or deeper (> 100 mm)

Propagate from seed and vegetative

Usually broad leaved weeds

Can germinate shallow (on soil surface) or from greater depths (>150 mm)

Can be annual, biannual and perennial

Propagate predominantly from seed

Yellow and red nutsedges but also exotics like Bulbostylus

Germinate from both seed (shallow) and tubers (deeper >200 mm)

Propagate from seed and vegetative

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Weed germination zones

Deep germinating weeds e.g. dicots and perennial grasses

Soil Surface

Shallow germinating weeds

Annual grasses and some broadleaved weeds e.g. Tagetes

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0 2 4 6 8 10 12 14 16

PA

EK

WEEKS

• Amaranthus

• Bidens pilosa

• Chloris

• Eleusine

• Schkuhria

• Urochloa

• Physalis

Weed species that peak early in the season followed by a gradual reduction in germination

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0 2 4 6 8 10 12 14 16

PE

AK

WEEKS

• Cleome

• Commelina

• Crotalaria

• Hibiscus (cannabis + trionum)

• Xantium

• Sorghum (halepense + bicolor)

• Bidens formosa

• Tribulus

• Panicum

• Digitaria

Weeds species with an initial peak followed by a second peak 8 - 15 weeks later:

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0 2 4 6 8 10 12 14 16

PE

AK

WEEKS

• Datura

• Portulaca

• Citrillus

• Cucumis

Weeds with a continuous germination pattern throughout the season.

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• Weeds use vast amounts of fertilizer that could be available for crop growth and development. Maize is especially prone to nutrient shortages during their early developmental stages.

• Research by Zimdahl* has shown that weed control in maize could be more beneficial than fertilizers because of the vast amount of fertilizers weeds use. Weeds use especially a lot of nitrogen compared to other nutrients.

Early weed control vs Nutrition

* Zimdahl, R. Weed/ Crop Competition: A Review, International Plant Protection Centre, Oregon State University, USA

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Nitrogen absorption by weeds and maize

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12

25 mm weeds 50 mm maize

Nit

rog

en

us

ed

(k

g/h

a)

No pre-emergence program Pre-emergence program

25 mm weeds, no pre-emergence program

Pre-emergence program

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0

5

10

15

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25

30

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75 mm weeds 200 mm maize

Nit

rog

en

us

ed

(kg

/ha

)

No pre-emergence program Pre-emergence program

75 mm weeds, no pre-emergence program

Pre-emergence program

Nitrogen absorption by weeds and maize

20PC Nel & JG Ehlers, Dept. Plant Production, University of Pretoria

N, P & K usage by weeds that grew unhindered

Weeks after emergence

N P K

2 1.4 0.1 1.1

3 3.3 0.3 2.1

4 21.6 2.2 17.7

5 27.8 2.4 21.8

6 93.7 5.4 57.2

7 94.8 5.5 78.4

13 122.9 11.2 109.1

During the first 13 weeks, weeds used the equivalent of

370 mm rain / ha

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Plant dry weight at maturity (g plant-1)

0 100 200 300

Pre-emergence weed control

Weed control just after 10-leaf

No Weed control

The effect of weeds on cob kernel number

500

400

300

200

100

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Ker

nel

nu

mb

er p

er p

lan

t

C. Swanton, E. Page, P. Westra, M Loux, A. Dobbels, K. Smith, J. Bullington, H. Wright and C. Foresman, 2009

Weed control just after 3-leaf

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• Even in glyphosate tolerant crops it is crucial to begin with a sound pre-emergence residual weed control programme when the plants full potential wants to be developed.

“Farmers should use a pre-emergence residual herbicide in the glyphosate tolerant system to help manage early season weed control. Growers can't afford

NOT to apply a pre-emergence herbicide in a glyphosate tolerant system. A pre-emergence residual herbicide in glyphosate tolerant soybeans and glyphosate tolerant maize protects against early season weed competition and can maximize

yield”

• Early season weed management has been embraced in Precision farming systems. Herbicide doses are applied differentially based on weed mapping of fields. Best results have been achieved when applied at early stages of weed growth.

The importance of pre-emergence weed control

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• There is need to adopt weed management programmes that result in the longer

residual effective in most situations for yield management

• The critical window for weed control is from emergence to the switching point (0-3

leaves). The theoretical potential is determined between the 1 – 5 leaf stage. Residual

weed control will aid in getting closer to the varieties‘ full potential.

• Pre-emergence weed control has a valuable role when considering resistance

management strategies.

In Conclusion :

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