Herbicide Resistant Weeds & Crops: A North American Perspective.

1. Herbicide Resistant Weeds & Crops: A North American Perspective. Tom Mueller University of Tennessee Knoxville, TN, USA

2. Overview of presentation • Herbicide resistant crops • How widespread? • Effect on weed control • Effect on development of herbicide resistance • Herbicide resistant weeds • Occurrence • Effect on farmers • My Perspective….

8. My perspective • Herbicide tolerant crops can be an emotional issue • If one wants to see a problem, one will see one • If one does not want to see a problem, one will not see one • As is often the case, we only see what we want to see…..

9. Defining a few terms • Herbicide Resistant Crop • Genetically Modified Organisms (GMOs) • Transgenic • Herbicide Resistance = • Inherited ability of a weed population to survive and reproduce after exposure to a herbicide dose (rate) that would control an unselected (sensitive) population

15. Glyphosate Tolerant Crops • RoundupReady (RR) varieties now common in USA • Soybean (>90%) • Cotton (70%) • Corn (~50%, still increasing) • Canola (not a US crop, but in Canada) • Mainly Monsanto Ag Products

17. Why do US farmers like RR? • The System works!! • Kills many weeds, both small and large • Crop safety, can have overlaps • Safe to people spraying (glyphosate is not toxic) • Monsanto owns seed companies…. • System is simple • One chemical… very easy

18. Other types of HT crops • LibertyLink Crops (Bayer) • Tolerant to glufosinate • Canola • Corn, soybeans • Some very promising lines

19. Some resistance to GMOs • In practice, the United States has conducted a large-scale feeding trial • ~300 million US citizens have consumed GMO crops for ~ 12 years. • No negative dietary effects • None… • There is no toxicological reason not to allow GMO crops to be used.

20. Herbicide Resistant Weeds • Weeds have been adapting to herbicide use for many years • Selection pressure allows for survivors to make seed and fill that open niche

22. (Conyza canadensis) (Amaranthus palmerii)

23. Distribution of HR weeds • More prevalent where glyphosate continually used • Cotton/soybean farms • Southeastern United States

24. Two main weedy species • Conyza canadensis • Winter annual • Amaranthus palmerii • Summer annual

25. Conyza canadensis • Very widespread • Several million hectares infested • Only a problem in no-tillage systems • Farmers using additional chemicals • 2,4-D/dicamba + flumioxizan prior to planting

26. (Conyza canadensis)

27. Photo credit: Chism Craig

28. Conyza canadensisResistant to glyphosate in TN • Wind-blown seed • Need more herbicides • Need more tillage Photo courtesy of Chism Craig

31. Amaranthus palmerii • Dioecious summer annual • Prolific seed producer • Can grow 2.5 cm/day in summer • Greatly reduces crop yield

33. Cotton field 2004 0.8 kg ae/ha glyphosate 14 DAA

34. West Tennessee 2008 4 kg/ha glyphosate in 1st spray 3 kg/ha glyphosate applied in 2nd application

35. HR Weeds effect on Farmers • Use more herbicides • In extreme cases, hire people to hoe the fields • Still using RR crop varieties

36. Other areas • Canada, upper midwest US • Minimal glyphosate Resistance problems • No GMO wheat • GMO canola has several modes of action • 50% RR, 30% LL, 15% Imi, 5% non HT • Can rotate between alternate modes of action • Other weeds have developed resistance • ACCase or ALS resistance

37. Over the larger area • “Most” farmers have no “major” weed resistance problems • More farmers will have HR weeds in the next few years • As RR corn use increases, will see more HR problems

38. The most common problem • RR corn “volunteers” in soybeans • A RR crop (corn) becomes a weed in a different RR crop (soybeans)

39. Do you see RR corn plants?

40. Final thoughts • HT crops widely used • Few HR weeds, but more each year • Once a farmer gets them, is a major problem

41. One sees what one wants to see…..

42. Questions?? • Canada