Crop Management - Dr. Robert G. Hartzler, Iowa State University - Managing Herbicide Resistance

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Attendees will gain a basic understanding of the processes influencing herbicide availability which is essential to diagnose performance issues in the field.

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Crop Management - Dr. Robert G. Hartzler, Iowa State University - Managing Herbicide Resistance

  1. 1. ManagingHerbicide Resistance Bob Hartzler Extension Weed Science Department of Agronomy
  2. 2. Evolution of Row Crop Weed Management Cultural + Chemical + Chemical mechanical mechanical1900 1920 1940 1960 1980 2000 2010
  3. 3. Important Resistant Weeds in IowaDecade Herbicides Weeds1980’s Triazines Pigweed, lambsquarter1990’s ALS inhibitors Waterhemp, cocklebur, foxtails, several others2000’s Glyphosate Waterhemp, horseweed, giant ragweed PPO inhibitors Waterhemp2010’s HPPD inhibitors Waterhemp www.weedscience.org
  4. 4. Resistance Mechanisms in WaterhempFamily Herbicides MechanismTriazines Atrazine, metribuzin Altered target site, Enhanced metabolismALS inhibitors Pursuit, Classic Altered target sitePPO inhibitors Blazer, Cobra, Reflex Altered target siteGlyphosate Roundup Target site amplification, perhaps othersHPPD inhibitors Callisto, Laudis UnknownGrowth regulators 2,4-D Unknown
  5. 5. Why Waterhemp?
  6. 6. Seed ProductionResistance is a numbers game Time of Soybean Corn emergence With crop 320,000 48,000 V4 20,000 2,000
  7. 7. ‘Standard’ Resistance Management Strategies• Fundamentals – Start with clean fields – Use weed-free seed – Scout fields – Control weed escapes – Clean equipment between fields www.monsanto.com www.resistancefighter.com
  8. 8. ‘Standard’ Resistance Management Strategies• Herbicide management – Rotate crops to allow alternate herbicides – Use multiple herbicides – Use full rates www.monsanto.com www.resistancefighter.com
  9. 9. ‘Standard’ Resistance Management Strategies• Miscellaneous tactics – . . . and add cultural practices – Consider mechanical control – Use cover crops www.monsanto.com www.resistancefighter.com
  10. 10. YEAR PRE POST MOA1999 Dual Basagran + atrazine 32000 Prowl Glyphosate 22001 Dual Callisto 22002 Prowl Glyphosate 22003 Dual Accent + atrazine (E-POST) 4 Callisto + atrazine (L-POST)2004 Prowl Glyphosate 22005 Dual Accent + Callisto + atrazine 42006 Prowl Glyphosate 22007 Dual Callisto + atrazine (E-POST) 3 Impact + atrazine (L-POST)2008 Prowl Glyphosate 22009 Dual Callisto + atrazine 3
  11. 11. Keys to Resistant Weed Management• Know your enemy• Optimize herbicide effectiveness
  12. 12. Evolution of Herbicide Rates Full label rate Acetochlor Flumetsulam ClopyralidPre RR 3 pts Harness + 2.6 lbs 0.9 oz 2.5 oz 5 oz HornetPost RR 2 pts SureStart 36% 50% 50%Post RRv2.0 3 pts SureStart 54% 75% 75% % herbicide remaining Waterhemp emergence # emerged/week April May June July
  13. 13. Keys to Resistant Weed Management• Cultural practices – Manipulation of cropping conditions to reduce the density and competitiveness of weeds or
  14. 14. Effects of Cultural Practices in Nebraska Wheat FieldsRow Direction Drill Type E-W N-S Disk Hoe40 630 420 210 0 0 LQ Pig Grass Fox Kochia Stinkgrass 8 Others Wicks et al. 2003. Weed Technol.
  15. 15. Value of Cultural Practices
  16. 16. Value of Cultural Practices Preemergence No PreGlyphosate at V3 Glyphosate at V3
  17. 17. Value of Cultural Practices
  18. 18. Cultural Practices For An Herbicide Era• Row spacing• Planting rate• Planting date• Variety characteristics
  19. 19. Herbicide Resistance• Weeds adapt to all tactics, all herbicides• The greater the reliance on a tactic, the greater the speed of adaption• Integrated management programs needed to stay ahead of evolution
  20. 20. Questions

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