1. Herbicide Resistance

2. Discussion Topics What is resistance? What causes resistance?

3. Terminology

5. Sites of Action Inhibition of ACCase Inhibition of ALS Inhibition of PS II PS I electron diversion Inhibition of PPO Bleaching: inhibition of carotenoid biosynthesis at PDS Bleaching: inhibition of HPPD Bleaching: inhibition of carotenoid biosynthesis, unknown target Inhibition of EPSPS Inhibition of glutamine synthetase Microtubule assembly inhibition Inhibition of long-chain fatty acid synthesis Inhibition of cell wall synthesis Inhibition of lipid synthesis; not ACCase inhibition Synthetic auxins Inhibition of auxin transport Unknown

8. WSSA Code Site of Action 1Inhibition of ACCase 2Inhibition of ALS 5Inhibition of PS II 22PS I electron diversion 14Inhibition of PPO 12Bleaching: inhibition of carotenoid biosynthesis at PDS 27Bleaching: inhibition of HPPD 13Bleaching: inhibition of carotenoid biosynthesis, unknown target 9Inhibition of EPSPS 10Inhibition of glutamine synthetase 3Microtubule assembly inhibition 15Inhibition of long-chain fatty acid synthesis 20 and 21Inhibition of cell wall synthesis 8Inhibition of lipid synthesis; not ACCase inhibition 4Synthetic auxins 19Inhibition of auxin transport 17Unknown

12. From 2011* NC AgChem Manual (>150 entries) Table 8-11. Herbicide Modes of Action. Brand names Active ingredient(s)Chemical family Mode of Action AAtrexatrazineTriazine5 AccentnicosulfuronSulfonylurea2 AimcarfentrazoneTriazolinone14 AlachloralachlorChloroacetamide15 AlanapnaptalamPhthalamate semicarbazone 19 ArrowClethodimCyclohexadione1 AtrazineatrazineTriazine5 Assure IIquizalofopAryloxyphenoxy- propionate 1 Axiomflufenacet + metribuzin Oxyacetamide + triazinone 15 + 5 BackdraftGlyphosate + imazaquin Glycine + imidazolinone 9 + 2 * Revised annually. Mode of Action Codes 1.ACCase inhibition 2.ALS inhibition 3.Microtubule assembly inhibition 4.Synthetic auxin 5.PS II inhibition, not groups 6 or 7 6.PS II inhibition, not groups 5 or 7 7.PS II inhibition, not groups 5 or 6 8.Lipid synthesis inhibition, not ACCase inhibition 9.EPSP synthase inhibition 10.Glutamine synthase inhibition 12.Carotenoid biosynthesis inhibition at PDS 13.Carotenoid biosynthesis inhibition, unknown target 14.PPO inhibition 15.Inhibition very long-chain fatty acids 17.Unknown MOA 19.Auxin transport inhibition 22.PS I electron diversion 27.Inhibition of HPPD

13. Herbicide Resistance Defined (WSSA definition) Inherited ability of a biotype* of a weed to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type. *Biotype is a subset of the population having some genetically controlled characteristic not common to the population as a whole

14. Herbicide Resistance Defined (WSSA definition) Inherited ability of a biotype of a weed to surviveand reproduce following exposure to a dose of herbicide normally lethal to the wild type.

15. Herbicide Resistance vs Tolerance Resistance: herbicide used to kill that weed; it no longer does; we have selected for resistance. Example: Hoelon and ryegrass Tolerance:the herbicide never did kill that species. Example: 2,4-D and ryegrass

16. Cause of Herbicide Resistance Herbicides do not create resistance. Herbicides can select for resistant individuals already in the population.

17. Resistant individuals initially rare Initial frequency of resistance: 1 in 100 thousand 1 in 1 million 1 in 10 million 1 weed/4.3 square feet = 10,000 weeds/acre = 1,000,000 weeds/100 acres Frequency of 1 in 1 million equal to one resistant plant per 100 acres

20. 0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X Hoelon-susceptible biotype Hoelon-resistant biotype, Union Co.; Treated with Hoelon Group 1, ACCase inhibitor Hoelon-resistant biotype, Union Co.; Treated with Axial Group 1, ACCase inhibitor Example of Cross Resistance Italian ryegrass

26. 0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X Hoelon-susceptible biotype Hoelon-resistant biotype Treated with Hoelon ACCase inhibitor, Group 1 Hoelon-resistant biotype Treated with Osprey ALS inhibitor, Group 2 0X 1/4X 1/2X 1X 2X 4X 8X 16X 32X Example of Multiple Resistance: Italian Ryegrass

27. Quiz Multiple resistance is greater concern than cross resistance. Why?

28. Discussion Topics What is resistance? What causes resistance? What is the extent of resistance? What species have resistant biotypes?

29. ACY 2008 ALS inhibitors PS II inhibitors (triazines) ACCase inhibitors Glyphosate DNAs Ureas/amides Auxins Arsenicals Thiocarbamates PPO inhibitors Carotenoid biosyn. inhibitors Nitriles Herbicide Resistance in US by Site of Action* Paraquat HPPD inhibitors *Current as of Dec. 6, 2010 Resistance reported with 14 SOAs and 76 species; 128 species by SOA combinations, due to multiple resistance

30. Glyphosate-resistant biotypes in U.S.

32. Glyphosate-Resistant Weeds in the US 7 Broadleaf weeds 5 Grasses Palmer amaranthItalian ryegrass Tall waterhempRigid ryegrass Common ragweedJohnsongrass Giant ragweedGoosegrass Hairy fleabaneAnnual bluegrass Horseweed Kochia

33. Examples of glyphosate multiple resistance in US Palmer amaranthglyphosate and ALS inhibitors Horseweedglyphosate and ALS inhibitors glyphosate and paraquat Common ragweedglyphosate and ALS inhibitors Giant ragweedglyphosate and ALS inhibitors Hairy fleabaneglyphosate and paraquat Tall waterhempglyphosate, ALS inhibitors, and PPO inhibitors

34. Glyphosate- Resistant Weeds in NC

35. Discussion Topics What is resistance? What causes resistance? What is the extent of resistance? What species have resistant biotypes? Impacts of herbicide resistance?

36. Impacts of Herbicide Resistance Increased cost of weed management; reduced profitability Increased complexity of weed management Fewer herbicide options Fewer crop options Compromise conservation tillage Impacts of Herbicide Resistance Increased cost of weed management; reduced profitability Increased complexity of weed management Fewer herbicide options Fewer crop options

37. Impacts of Herbicide Resistance Increased cost of weed management; reduced profitability Increased complexity of weed management Fewer herbicide options Fewer crop options Compromise conservation tillage Impacts of Herbicide Resistance Increased cost of weed management; reduced profitability Increased complexity of weed management Fewer herbicide options Fewer crop options Compromise conservation tillage

38. Discussion Topics What is resistance? What causes resistance? What is the extent of resistance? What species have resistant biotypes? Impacts of herbicide resistance? Basics of resistance management

39. How does herbicide resistance develop? Prerequisites for Resistance 1. At least one resistant plant must be present 2.Selection pressure must be put on that resistant plant

40. Herbicide Resistance Management The focus must be on reducing selection pressure.

41. Diversity in management options reduces selection pressure on herbicides.

43. Weed Management in Cotton: Before RR 1. Conventional tillage 2. PPI and PRE herbicides 3. Early POST or POST-directed herbicides 4. Late POST-directed herbicides 5. Cultivation

44. Weed Management in Cotton: with RR 1. No-till or strip-till 2. No cultivation 3. No PPI herbicide; little to no PRE 4. Multiple in-crop Roundup applications 5. Very little other chemistry

45. Herbicide Resistance Management (Reducing selection pressure) 1. Minimize seed bank; avoid seed production

46. Impact of Crop Rotation and Good Control in Rotational Crop (whole field in soybean in 2009; all treated alike in 2009) Carthage, NC 2009

47. Impact of Crop Rotation and Good Control in Rotational Crop (whole field in soybean in 2009; all treated alike in 2009) Carthage, NC 2009 Soybean 2008 Tobacco 2008

48. Herbicide Resistance Management (Reducing selection pressure) 1. Minimize seed bank; avoid seed production Think whole-farm Good control in all crops in rotation Avoid seed production on ditchbanks, turnrows Avoid seed movement

49. Herbicide Resistance Management 1. Minimize seed bank 2. Do not depend on a single herbicide (or a single SOA) a. Multiple SOAs within a crop, starting with a PRE or Preplant b. Crop rotation, multiple and different SOAs Herbicide Resistance Management (Reducing selection pressure)

50. Herbicide Resistance Management 1. Minimize seed bank 2. Do not depend on a single herbicide (or SOA) a.Multiple SOAs within a crop, starting with a PRE. b.Crop rotation, with different SOAs 3. Use full rates, including sequentials and tank mixes Herbicide Resistance Management (Reducing selection pressure)

51. Herbicide Resistance Management 1. Minimize seed bank 2. Do not depend on a single herbicide (or SOA) a.Multiple SOAs within a crop, starting with a PRE. b.Crop rotation, with different SOAs 3. Use full rates, including sequentials and tank mixes 4. Timely POST application Herbicide Resistance Management (Reducing selection pressure)

52. This is not a 4- inch pigweed!

53. Herbicide Resistance Management 1. Minimize seed bank 2. Do not depend on a single herbicide (or SOA) a.Multiple SOAs within a crop, starting with a PRE. b.Crop rotation, with different SOAs 3. Use full rates, including sequentials and tank mixes 4. Timely POST application 5. Start clean Herbicide Resistance Management (Reducing selection pressure)

54. 1. Minimize seed bank 2. Do not depend on a single herbicide (or SOA) a.Multiple SOAs within a crop, starting with a PRE. b.Crop rotation, with different SOAs 3. Use full rates, including sequentials and tank mixes 4. Timely POST application 5. Start clean 6. Take advantage of non-chemical, cultural practices where applicable (tillage, narrow rows, planting dates, cover crops, etc.) Herbicide Resistance Management

55. &

56. Discussion Topics What is resistance? What causes resistance? What is the extent of resistance? What species have resistant biotypes? Basics of resistance management Management of glyphosate-resistant weeds in NC

57. Glyphosate- Resistant Weeds in NC

58. 96 oz Weathermax Untreated Martin Co., NC 2006

61. Grower Applied Glyphosate; Dead and Live Plants; Union Co., NC. Spring, 2009.

62. Johnston Co. susceptible Stanley Co. Union Co. Edgecombe Co. susceptible Glyphosate rates, left to right, where 1X = 860 g/ha or 21.8 fl oz PowerMax 0.063X, 0.125X, 0.25X, 0.5X, 1X, 2X, 4X, 8X 1X 8X Dec. 2009

64. Burndown for Glyphosate-Resistant Ryegrass If you suspect glyphosate resistance: –Minimum of 2 pt/A Gramoxone applied twice. –Better control if mixed with a Photosystem II inhibitor: atrazine for corn; Direx for cotton; linuron or metribuzin product for soybean

65. Gramoxone 3 pt Mar. 9PowerMax 22 oz Mar. 9 Gramoxone 2 pt Mar. 9 Gram 2 pt + atrazine Mar. 24 PowerMax 22 oz Mar. 9 PowerMax 22 oz + atrazine Mar. 24 Untreated C. Simpson Farm Apr. 10, 2010 Union County

67. Glyphosate-Resistant Horseweed Initially found in 2003; resistant biotype spread quickly beginning in 2008; assume all horseweed in eastern NC is resistant. Wind-borne seed; easily moves long distances. Problem in no-till. Postemergence options limited. Focus on good burndown program. Photo by R. Hayes

68. Burndown Program for Glyphosate-Resistant Horseweed Two components of burndown program: 1. Something to kill emerged horseweed 2. Something to give residual control

69. Burndown Programs for Glyphosate-Resistant Horseweed Two components of burndown program: 1. Something to kill emerged horseweed* 2. Something to give residual control Programs: Glyphosate + Clarity (1/2 pt)** + residual herbicide Glyphosate + 2,4-D (2 pt)** + residual herbicide *Best if applied while weed still in rosette state __________________________________ ** Waiting intervals required

70. Edgecombe Co., 2008 GR Horseweed Roundup at burndown Roundup + 2 pt 2,4-D + 2 oz Valor at burndown

71. In-Crop Control of Glyphosate-Resistant Horseweed Cotton:Ignite under hood (any variety) Ignite overtop tolerant variety Corn:Dicamba or 2,4-D Ignite on LL hybrid Soybean: FirstRate, horseweed < 6 inches Ignite overtop LL variety

76. What Makes Palmer Amaranth Such a Bad Weed? Heat and drought tolerant High photosynthetic capacity Rapid growth; large stature Very prolific Resistance trait transferred via pollen

77. 4 in 52 hrs

78. Can have thousands of seed 99% control is a disaster per square yard in seed bank; hundreds emerge per square yard

81. Untreated Atrazine-based program

83. GR Palmer Amaranth Control in RR Cotton Southeast US Recommendations Avoid cotton in badly infested fields; rotate out of cotton for a year or more and strive for good control in rotational crop; reduce seed bank

84. Palmer Amaranth Programs for Corn POST PRERR CornLL CornConventional BicepHalex GT + atrazineIgnite + atrazineCapreno + atrazine Guardsman Max Roundup + atrazineClarity + atrazine Harness Extra Roundup + Dual II Magnum* Laudis + atrazine LariatRoundup + Warrant* LexarRoundup + Clarity *No activity on emerged glyphosate-resistant weeds.

85. Palmer Amaranth Programs for Soybeans PPO PREsNon-PPO PREsPOST Authority MTZ + grass herbicide BoundaryRoundup + Blazer Envive + Prowl Canopy + grass herbicide Roundup + Cobra Prefix*Roundup + Flexstar* Valor + ProwlRup + Harmony SG** Roundup + Prefix* Roundup + Pursuit** *Contains fomesafen. Only one application per year. **ALS inhibitor.

86. Glyphosate-resistant Palmer amaranth, Wayne Co., NC 2008; PRE herbicide followed by timely glyphosate tank mix

87. GR Palmer Amaranth Control in RR Cotton Southeast US Recommendations Avoid cotton in badly infested fields Aggressive Preplant and/or PRE herbicide program. Get it PRE or you dont get it. No salvage POST options in RR or conventional cotton.

88. Hedging Against Lack of Timely Rain on PRE Herbicides: Palmer Amaranth in Cotton or Soybeans In conventional tillage, incorporate a yellow herbicide. In no-till cotton or no-till full-season soybeans, put residual with preplant burndown. Paraquat if needed at planting. In double-crop soybeans, pray for rain.

89. Preplant/PRE herbicides for Palmer amaranth in Cotton Preplant PPI no-tillconv. till PRE ValorTreflanCotoranDiuron + Staple DirexProwlDiuronReflex + Staple ReflexReflex + Cotoran StapleReflex + diuron ProwlProwl + Reflex Prowl + Cotoran Prowl + diuron

90. Avoid cotton in badly infested fields Aggressive Preplant and/or PRE herbicide program. Dual Magnum or Warrant early POST Residual lay-by GR Palmer Amaranth Control in RR Cotton Southeast US Recommendations

91. Weed control with glufosinate-based systems

92. Weed Management in Glufosinate-Tolerant Cotton Weaknesses of Ignite: grasses, pigweed sp., nutsedge, perennials Ignite not as effective as glyphosate on grasses, perennial weeds, or glyphosate-susceptible Palmer, but it will control glyphosate-resistant Palmer if properly timed Left: 29 oz Ignite Right: 22 oz Powermax GR Palmer amaranth,14 days after treatment

93. Timing is critical!! 3 to 4 inches for consistent Palmer control. Use additional chemistry, similar to RR program Better control, Ignite timing somewhat less critical Absolutely must avoid Ignite resistance Strong PRE and/or preplant program for residual control Dual or Warrant POST for additional residual control Residual lay-by Weed Management in Glufosinate-Tolerant Cotton

94. 1. Minimize seed bank 2. Do not depend on a single herbicide (or SOA) a.Multiple SOAs within a crop, starting with a PRE. b.Crop rotation, with different SOAs 3. Use full rates, including sequentials and tank mixes 4. Timely POST application 5. Start clean 6. Take advantage of non-chemical, cultural practices where applicable (tillage, narrow rows, planting dates, cover crops, etc.) Herbicide Resistance Management (Reducing selection pressure)

95. Harrington Seed DestructorRay Harrington Western Australia

98. No Deep TillageDeep Turn No Herbicide Treatment Number of Palmer Amaranth Plants During Early Season. Macon Co., Georgia 2008.*

100. 81 b No deep turn No Cover Deep turn No cover Rye 7 foot when killed, rolled, planted. Deep turn 12 inch in previous fall. Herbicide program: Direx + Reflex + Staple PRE; RU + Parrlay POST, Direx + MSMA at layby. percent 63 c 80 b 98 a GR Palmer amaranth control at harvest with Roundup-based systems. Macon Co., GA 2009. No deep turn Rye Cover Deep turn Rye Cover

101. 1627 b No deep turn No Cover Deep turn No cover Rye 7 foot when killed, rolled, planted. Deep turn 12 inch in previous fall. Herbicide program: Direx + Reflex + Staple PRE; RU + Parrlay POST, Direx + MSMA at layby. 1298 d 1524 bc 2078 a Seed cotton yield (lb/A) with Roundup-based systems. Macon Co., GA 2009. No deep turn Rye Cover Deep turn Rye Cover

102. Staple + Reflex + Direx PRE Roundup WMax + Parrlay POST Direx + MSMA Layby No deep tillage No cover crop Deep tillage No cover crop Palmer amaranth response to deep tillage. Macon County, GA. 2009.

103. Staple + Reflex + Direx PRE Roundup WMax + Parrlay POST Direx + MSMA Layby No deep tillage No cover crop No deep tillage Rye cover crop Palmer amaranth response to cover crops. Macon County, GA. 2009.

104. Staple + Reflex + Direx PRE Roundup WMax + Parrlay POST Direx + MSMA Layby No deep tillage No cover crop Deep tillage Rye cover crop Palmer amaranth response to deep tillage and cover crops. Macon County, GA. 2009.

105. Seed concentrated on surface in no-till system. Palmer amaranth seed will not emerge from deeper than about 1 inch. Seed viability reduced 80% 30 months after burial. Fall plowing every 3 to 5 years, followed by cover crop established in same fall, then no- till for 3 to 5 years.

108. Staple + Reflex + Direx PRE Roundup WMax + Parrlay POST Direx + MSMA Layby No deep tillage No cover crop Palmer amaranth response to deep tillage and cover crops. Macon County, GA. 2009. Staple + Reflex + Direx PRE Ignite + Parrlay POST Direx + MSMA Layby No deep tillage No cover crop

109. Percent reduction in Palmer emergence by cover crops without herbicides. GA and NC. 2007. 42 DAP.* *Compared to the no cover conventionally tilled system. 38 b 53 ab 40 b 57 a wheat biomassrye biomass