February 3-4th, 2014 Wad Medani, Sudan Early Season Weed Management-Syngenta Perspective

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3 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

4 Yield Management Irreversible yield losses Yield maximization switching point

5 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: Moisture Nutrients Evaporation Root development Light interception

6 Optimal window for weed Management in maize BEFORE the switching point is reached A maize plants theoretical yield potential is determined between the 1 – 5 leaf

7 Key Features Strategy must have an economical as well as environmental consideration Weeds dont 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:

8 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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10 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

11 Weed types MONOCOTSDICOTS 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

12 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

14 PAEK WEEKS Amaranthus Bidens pilosa Chloris Eleusine Schkuhria Urochloa Physalis Weed species that peak early in the season followed by a gradual reduction in germination

15 PEAK 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 weeks later:

16 PEAK WEEKS Datura Portulaca Citrillus Cucumis Weeds with a continuous germination pattern throughout the season.

17 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

18 Nitrogen absorption by weeds and maize 25 mm weeds, no pre-emergence program Pre-emergence program

19 75 mm weeds, no pre-emergence program Pre-emergence program Nitrogen absorption by weeds and maize

20 PC Nel & JG Ehlers, Dept. Plant Production, University of Pretoria N, P & K usage by weeds that grew unhindered Weeks after emergence NPK During the first 13 weeks, weeds used the equivalent of 370 mm rain / ha

21 Plant dry weight at maturity (g plant -1 ) Pre-emergence weed control Weed control just after 10-leaf No Weed control The effect of weeds on cob kernel number Kernel number per plant 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

22 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

23 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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