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Herbicide Resistant Weeds and Their Management

AUTHOR
Eric P. Prostko
A. Stanley Culpepper
Extension Weed Specialists
The University of Georgia
Tifton, GA

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TABLE OF CONTENTS
  1. Herbicide Resistant Weeds and Their Management
  2. Herbicide Resistance Definition
  3. Herbicide Resistance
  4. Why Are Plants Resistant to Herbicides?
  5. Altered Site of Action
  6. Herbicide Resistance
  7. Herbicide Resistant Weeds - Selection Pressure
  8. Herbicide Resistance - Around the World
  9. The Beginning of Weed Resistance
  10. The Chronological Increase in Unique Cases of Herbicide-Resistant Weeds Worldwide
  11. Weed Characteristics That Favor Resistance
  12. Most Important Herbicide-Resistant Species
  13. Average Number of Seed Produced per Plant
  14. Herbicide Characteristics That Influence Weed Resistance
  15. Herbicide Resistant Weeds By Mode of Action
  16. Commonly Used ALS Herbicides
  17. Herbicide Resistance in Georgia
  18. Other Counties in Georgia with ALS-Resistant Palmer Amaranth
  19. Glyphosate Resistance Around the World (8 species)
  20. Glyphosate Resistant Horseweed in US (confirmed in 12 states)
  21. Other Weeds in the U.S. that have Developed Resistance to Glyphosate
  22. U.S. Acres Treated with Glyphosate 1996-2003
  23. Herbicide Resistance Should Only Be Suspected When ...
  24. MSMA Resistant Cocklebur in NC
  25. Causes of Herbicide Failures
  26. Herbicide Resistant Weeds - Strategies for Control/Prevention
  27. How long does resistance last in absence of further selection pressure?
  28. Does the use of reduced rates influence the rate of herbicide resistance development ?
  29. More Information About Herbicide Resistance



SLIDE CONTENTS
  1. Herbicide Resistant Weeds and Their Management Eric P. Prostko and A. Stanley Culpepper Extension Weed Specialists The University of Georgia Updated October 2005
  2. Herbicide Resistance Definition inherited ability of a weed or crop biotype to survive a herbicide application to which the original population was susceptible. Biotype = a group of plants within a species that has biological traits that are not common to the population as a whole.
  3. Herbicide Resistance cross resistance * weed biotype that has gained resistance to more than 1 herbicide with the same mode of action. Same or different families. multiple resistance * weed biotype that has developed tolerance to more than one herbicide brought about by different selection pressures (different modes of action).
  4. Why Are Plants Resistant to Herbicides? altered site of action enhanced metabolism sequestration
  5. Altered Site of Action Source: J.L. Gunsolus. Herbicide Resistant Weeds. 1998. North Central Region Extension Publication 468.
  6. Herbicide Resistance How does it occur?
  7. Herbicide Resistant Weeds Selection Pressure Source: J.L. Gunsolus. Herbicide Resistant Weeds. 1998. North Central Region Extension Publication 468.
  8. Herbicide Resistance Around the World 304 Resistant Biotypes 182 Species (109 dicots and 73 monocots) over 270,000 fields Source: Heap, I. The International Survey of Herbicide Resistant Weeds. Online. Internet. October 20, 2005 .
  9. The Beginning of Weed Resistance 1968 (Washington) nursery crops common groundsel atrazine simazine Photo: The Missouri Flora Web-Site
  11. Weed Characteristics That Favor Resistance reproductive capability seed dispersal mechanisms
  12. Source: Dr. Ian Heap (www.weedscience.com) Worldwide
  13. Average Number of Seed Produced per Plant Top 4 Herbicide Resistant Weeds in US peanut - 175; cotton - 250; corn - 800
  14. Herbicide Characteristics That Influence Weed Resistance herbicides with a single site of action herbicides used multiple times during the growing season herbicides used for consecutive growing seasons herbicides used without other control strategies repeated use of a product for more than 2 years could develop a herbicide resistance problem!!
  15. Herbicide Resistant Weeds By Mode of Action
  16. Commonly Used ALS Herbicides Accent Ally Beacon Cadre Classic Envoke Exceed Express Harmony Extra Peak Permit Pursuit Python Scepter Staple Strongarm
  17. Herbicide Resistance in Georgia
  18. Other Counties in Georgia with ALS-Resistant Palmer Amaranth Tested by BASF in 2005 Colquitt Cook Mitchell 175 locations were also sampled by UGA weed scientists in 2005 * * *
  19. Glyphosate Resistance Around the World (8 species) rigid ryegrass (1996) goosegrass (1997) horseweed (2000) Italian ryegrass (2001) hairy fleabane (2003) buckhorn plantain (2003) common ragweed (2004) Palmer amaranth (2005)
  20. Glyphosate Resistant Horseweed in US (confirmed in 12 states) DE (2000) TN (2001) IN (2002) MD (2002) NJ (2002) OH (2002) AK (2003) MS (2003) NC (2003) OH (2003) PA (2003) CA (2005) Horseweed pictures from SWSS Weed ID Guide
  21. Other Weeds in the U.S. that have Developed Resistance to Glyphosate Palmer amaranth (GA-2005) Common ragweed (MO-2004) Rigid ryegrass (CA-1998) Italian ryegrass (OR-2004) SWSS SWSS L. Hall - UGA USDA
  22. U.S. Acres Treated with Glyphosate 1996-2003 Source: USDA - National Agricultural Statistics Service – Agricultural Chemical Usage Reports
  23. Herbicide Resistance Should Only Be Suspected When .……... other causes of herbicide failure have been ruled out. the same herbicide or herbicides with the same mode of action have been used year after year. one weed that is normally controlled is not controlled while other weeds are. healthy weeds are mixed with controlled weeds (same species) a patch of uncontrolled weed is spreading.
  24. MSMA Resistant Cocklebur in NC (Dr. Alan York – NCSU))
  25. Causes of Herbicide Failures weed size** moisture temperature humidity rate application method calibration others All possible reasons for poor performance should be investigated before considering the possibility of resistance!!!
  26. Herbicide Resistant Weeds Strategies for Control/Prevention proactive vs. reactive utilize other weed control tactics (cultivation, row patterns, etc.) rotate herbicides with different MOA rotate crops scout fields prevent seed production clean tillage and harvesting equipment
  27. How long does resistance last in absence of further selection pressure? Andrews and Morrison (1997) - Canada DNA resistant green foxtail % of resistant seeds after 7 years initial resistance was at least 90% Source: Weed Technology (1997): 11:369-372.
  28. Does the use of reduced rates influence the rate of herbicide resistance development ? some say yes, some say no single dominant gene or multi-genic? Is level of control is same? rate vs selection pressure infrequent use of the lowest rate that provides effective control
  29. More Information About Herbicide Resistance UGA Weed Science Web-Site * http://gaweed.com International Survey of Resistant Weeds * http://www.weedscience.org/in.asp