Managing g Weeds and Weed Resistance Challenges

Transcription

1 Managing g Weeds and Weed Resistance Challenges South Asia Conference on Current Approaches to the Environmental Risk Assessment of Genetically Engineered Crops May 16-18, 2011 Donald J. MacKenzie

2 Weeds are a Major Cause of Yield Losses 5-7 DAP DAP DAP DAP DAP DAP DAP DAP Experiments in Zambia studied the effects of weeds on maize yields using weeding methods typical of small farms where eeoxen aeused are for cultivation. Losses of 30% were evident with common weeding practices. Crop needs to be kept clean from DAE. Source: R. Vernon and J.M.H. Parker. Maize/Weed Competition Experiments: Implications for Tropical Small Farm Weed Control Research. Cambridge University Press, 19: , 1983.

3 What is Weed Resistance? The evolved capacity of a previously herbicide-susceptible weed population p to withstand a herbicide and complete its life cycle when the herbicide is used at its normal rate in an agricultural situation (Source: Heap and Lebaron in Herbicide Resistance and World Grains). HPPD, ALS and triazine resistant Tall Waterhemp (Amaranthus tuberculatus) in Iowa Photo by Allan Nieves

4 Most Weed Resistance is Unrelated to GMHT Traits Globally, 357 Resistant Biotypes, 197 Species (115 dicots and 82 monocots) Eventually, weed resistance happens with all modes of action Introduction of Introduction of GMHT crops

5 How Weeds Become Resistant to Herbicides Within a weed population, a very small number of individuals have rare genetic mutations making them herbicide resistant Mechanisms of resistance Target site Altered herbicide binding site Enhanced metabolism Ability to metabolize herbicides Decreased translocation Reduced movement of the herbicide to site of action Sequestration Storage of herbicide in tissues isolated from the site of action Weeds can also display cross-resistance Single resistance mechanism - resistance to more than one herbicide Multiple resistance - two or more resistance mechanisms are present in the same plant Ian Heap, CropLife White Paper: Weed Resistance Management in Herbicide Tolerant Crops

6 Herbicide MOAs vary significantly by Risk of Selection for target-site resistance High Moderately High Moderate Low- Moderate ALS and ACCase HPPD? PSII (triazines) PPO? DNAs and Thiocarbamates PsII (ureas), Paraquat, and other* Herbicides in the low to moderate group Low Auxins, PsII (nitriles), glyphosate, and glufosinate High risk < 10 applications, Moderate = 11-20, Low > 20 applications *Insufficient i information (HPPD, PPO) Source: Beckie, H.J., 2006, Weed Technol.

7 Primary Factors affecting Herbicide id Resistant t Weed Development Herbicide id selection pressure (factors) Efficacy very high or marginal Recurrent applications lack of herbicide diversity Specificity it of site of action Weed factors High population densities Prolific seed producers Widely distributed Genetically variable = large soil seed pool Efficient seed or pollen dissemination (including out-crossing and movement on farm machinery) Simple cropping systems (monocultures ie. annual row crops) Favor a few dominant weed species

8 Weed Resistance: Why You Can t See It Coming Year 0 Treatment % Resistant Weeds in total population Weed control 0 Application.0001 Excellent 1 st Application Excellent 2 nd Application.0205 Excellent 3 rd Application.294 Excellent 4 th Application 4.22 Excellent 5 th Application 60.5 Failure mutant resistant biotype seed pool or seed bank in soil First application of herbicide to the base population

9 Weed Resistance: Why You Can t See It Coming Year 1 Treatment % Resistant Weeds in total population Weed control 0 Application.0001 Excellent 1 st Application Excellent 2 nd Application.0205 Excellent 3 rd Application.294 Excellent 4 th Application 4.22 Excellent 5 th Application 60.5 Failure seed pool or seed bank in soil After first application, the resistant individual survives the treatment and produces seed

10 Weed Resistance: Why You Can t See It Coming Year 2 Treatment % Resistant Weeds in total population Weed control 0 Application.0001 Excellent 1 st Application Excellent 2 nd Application.0205 Excellent 3 rd Application.294 Excellent 4 th Application 4.22 Excellent 5 th Application 60.5 Failure seed pool or seed bank in soil Control is still excellent, but resistant seed continues to increase

11 Weed Resistance: Why You Can t See It Coming Year 3 Treatment % Resistant Weeds in total population Weed control 0 Application.0001 Excellent 1 st Application Excellent 2 nd Application.0205 Excellent 3 rd Application.294 Excellent 4 th Application 4.22 Excellent 5 th Application 60.5 Failure seed pool or seed bank in soil Control is still good, but resistant seed continues to increase

12 Weed Resistance: Why You Can t See It Coming Year 4 Treatment % Resistant Weeds in total population Weed control 0 Application.0001 Excellent 1 st Application Excellent 2 nd Application.0205 Excellent 3 rd Application.294 Excellent 4 th Application 4.22 Excellent 5 th Application 60.5 Failure seed pool or seed bank in soil Control may still appear acceptable, but the seed pool is almost completely shifted to the resistant type

13 Weed Resistance: Why You Can t See It Coming Year 5 Treatment % Resistant Weeds in total population Weed control 0 Application.0001 Excellent 1 st Application Excellent 2 nd Application.0205 Excellent 3 rd Application.294 Excellent 4 th Application 4.22 Excellent 5 th Application 60.5 Failure * Martin, A. Univ. of Neb. In many cases, the seed pool is unlikely to shift back because there is little fitness penalty seed pool or seed bank in soil Weed plants and seed pool are now mostly resistant

14 Preserving the Herbicides Available Far fewer companies 1970 s there were over 40, now only ~ 7 Diminishing returns on research 1950 Screen 1,000 compounds per commercial product Now Screen 150,000 compounds Cost to develop and register a pesticide is now ~$250 mil (US) Last new herbicide MOA patent filed in 1982! Combinatorial chemistry has not been useful Bio-rational design has not been successful Duke, 2011, WSSA

15 The Future Challenge No new herbicide id MOAs visible ibl in the next decade d Continued increase in HT crop cultivation Multiple herbicide resistant weeds are increasing How do we preserve the effectiveness How do we preserve the effectiveness of current herbicides?

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17 Grower Education: A Critical Component for Success Growers informed and educated about potential for herbicide weed resistance and possible impact on TOTAL weed control program Growers understand best management practices and put together total weed control programs that will meet their needs and minimize chance for development of resistant weed populations Growers need to scout regularly and be on lookout for weed escapes hard to see coming Report suspected weed resistance issues Everyone needs to understand that a silver bullet new herbicide MOA is not coming soon KEY - preserve the limited choices available Farmer Education and Planning Is Essential For Successful Farmer Education and Planning Is Essential For Successful Weed Resistance Management

18 Best Management Practices to Minimize Weed Resistance 1. Use of herbicide id tolerant t crops does not limit it growers to use one herbicide id product. Conventional herbicides can and should still be part of a growers overall management system 2. Use multiple herbicide modes-of-action of with overlapping weed spectrums in rotation, sequences, or mixtures. 3. Use the full recommended herbicide rate and proper application timing for the hardest to control weed species present in the field. 4. Scout fields after herbicide application to ensure control has been achieved. Avoid allowing weeds to reproduce by seed or to proliferate vegetatively. 5. Use alternative weed management practices, such as crop rotation, mechanical cultivation, and delayed planting 6. Clean equipment before moving between fields to minimize dispersion of weed seed this has been a major source of spread in the U.S.

19 Best Management Practices to Minimize Weed Resistance in Annual Cropping Systems Specifically for annual cropping systems Start with a clean field and control weeds early by using a burndown treatment or tillage in combination with a preemergence residual herbicide as appropriate. Use cultural practices such as cultivation and crop rotation, where appropriate. Use good agronomic principles that enhance crop competitiveness Farmer Education and Planning Is Essential For Successful Farmer Education and Planning Is Essential For Successful Weed Resistance Management