Published on September 3, 2007
Slide1: Herbicide Resistant Weeds W. W. Witt University of Kentucky Slide2: World Problem: World Problem 307 Resistant biotypes 183 species 110 broadleaves 73 monocots (grasses andamp; sedges) 270,000 fields Weed Science Society of America“Official Definition”: Weed Science Society of America 'Official Definition' Herbicide Resistance : 'Herbicide resistance is the inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type. In a plant, resistance may be naturally occurring or induced by such techniques as genetic engineering or selection of variants produced by tissue culture or mutagenesis.' Another: The evolved capacity for a previously herbicide-susceptible weed population to withstand a herbicide and complete its life cycle when the herbicide is used at it normal rate in an agricultural situation (Heap andamp; Lebaron, 2001) Herbicide Resistant Weeds: Herbicide Resistant Weeds Resistant: Weed not killed at any rate Practical Resistance: Weed not killed at the labeled herbicide rate Herbicide Resistant Weeds: Herbicide Resistant Weeds Biotype: subpopulation of a species with characteristics that set it apart from the rest of the species Selection: process by which control measures favor resistant weeds over susceptible weeds. Intensity increases with the level of control. Slide7: Herbicide Resistant Weeds in Various Herbicide Groups 2006: Herbicide Resistant Weeds in Various Herbicide Groups 2006 Herbicide Resistant Weeds in Various Herbicide Groups 2006: Herbicide Resistant Weeds in Various Herbicide Groups 2006 Resistance: Resistance Cross Resistance: plant is resistant to several herbicides with the same site of action Multiple Resistance: plant is resistant to several herbicides with different sites of action Development of Herbicide Resistance by Herbicide Chemistry and Time : Development of Herbicide Resistance by Herbicide Chemistry and Time Slide12: Slide13: Slide14: Slide15: Slide16: Glyphosate Resistance in U.S.: Glyphosate Resistance in U.S. 2005 Palmer amaranth GA 2004 Common ragweed MO, AR 2000- Horseweed (marestail) 13 states 2005 2004 Italian ryegrass OR Where Do Resistant Weeds Come From?: Where Do Resistant Weeds Come From? Already present in the field Occur at very low frequency andlt; 1 resistant plant / million plants Herbicide selection allows the resistant biotypes to increase How Fast Can Resistant Weeds Increase?: How Fast Can Resistant Weeds Increase? 2000--1 plant produces 8000 seeds 2001--20% of seeds germinate= 1600 plants X 8000 seeds/plant= 12,800,000 seeds 2002--12,800,000 seeds X 20%= 2,560,000 plants X 8000 seeds/plant = 20,480,000,000 seeds Case Study of a Resistant WeedALS Smooth Pigweed in KY: Case Study of a Resistant Weed ALS Smooth Pigweed in KY 1986: Scepter, full season soybeans ALS 1987: Corn, atrazine 1988: Scepter, double crop soybeans ALS 1989: Corn, atrazine 1990: Scepter, double crop soybeans ALS 1991: Scepter pre, ALS post, soybeans ALS 1992: Scepter pre, ALS post, soybeans ALS 1993: Grain sorghum, atrazine 1994: Scepter pre ALS, Pursuit post ALS, Pinnacle post, ALS Cobra post PPO Biochemical Basis for Smooth Pigweed Resistance to ALS Herbicides: Biochemical Basis for Smooth Pigweed Resistance to ALS Herbicides Amino Acid Sequence Susceptible pigweed VQTEDRFYKA Tryptophane Resistant pigweed VQLEDRFYKA Leucine Schmenk andamp; Barrett, Univ. of KY Herbicide Management and Resistance:Factors That Encourage Resistance: Herbicide Management and Resistance: Factors That Encourage Resistance Herbicide acting at a single site Multiple Applications Long soil residual activity Total reliance on herbicides High level of herbicidal control Biological FactorsWeed biology/ecology: Biological Factors Weed biology/ecology Seed life in soil Fitness of resistant weeds Seed production by resistant weeds The above differ for each resistant weed species Slide24: Repeated use of a herbicide or class of herbicides with the same 'mode of activity' puts selection pressure on the weed population Multiple Herbicide ResistanceWorst Case Scenario: Multiple Herbicide Resistance Worst Case Scenario Annual ryegrass (L. rigidum) in Australia Resistant to every known class of herbicides Resistant to herbicides never used to control it Multiple mechanisms: altered target sites, detoxification, sequestration Diagnosis of Resistance: Diagnosis of Resistance Suspected in field single species escape patches or whole field Same herbicide or same site of action (SA) failed before Same herbicide or SA used frequently Greenhouse / Laboratory confirmation Herbicide Resistant Weeds andHerbicide Tolerant Crops: Herbicide Resistant Weeds and Herbicide Tolerant Crops Are we headed for trouble? How do we manage crops and weeds? How do we keep volunteer crops from becoming serious weeds? Herbicide Resistance Weeds in Kentucky: Herbicide Resistance Weeds in Kentucky Triazines smooth pigweed ALS inhibitors smooth pigweed giant ragweed? ACCase inhibitors johnsongrass annual ryegrass Glyphosate horseweed ALS Accent Johnsongrass 2006 Risk of New Herbicide Resistant Weeds: Risk of New Herbicide Resistant Weeds Will depend on: Herbicide chemistry Management of herbicide use by growers Using herbicides with low risk for resistance HIGH RISK of developing resistance: HIGH RISK of developing resistance Amino Acid Synthesis Inhibitors (ALS Inhibitors) Accent (nicosulfuron) Beacon (primisulfuron) Canopy EX (chlorimuron + tribenuron) Classic (chlorimuron) Equip (foramsulfuron + iodosulfuron- methyl) Escort (metsulfuron methyl) Everest (flucarbozone) Exceed (primisulfuron + prosulfuron) FirstRate, Amplify (cloransulam) Frontrow (cloransulam + flumetsulam) Harmony Extra (thifensulfuron + tribenuron) Harmony GT (thifensulfuron) Lightning (imazapyr + imazethapyr) Option (foramsulfuron) Permit (halosulfuron) Pursuit (imazethapyr) Python (flumetsulam) Raptor (imazamox) Scepter (imazaquin) Spirit (prosulfuron + primisulfuron) Steadfast (rimsulfuron + nicosulfuron) Synchrony STS (chlorimuron + thifensulfuron) Lipid Synthesis Inhibitors ACCase Inhibitors Achieve (tralkoxydim) Arrow (clethodim) Assure II (quizalofop) Fusion (fluazifop + fenoxaprop) Hoelon (diclofop-methyl) Poast, Poast Plus (sethoxydim) Select, Volunteer (clethodim) MEDIUM RISK of developing resistance: MEDIUM RISK of developing resistance Photosynthesis Inhibitors (Photosystem II) Atrazine Basagran (bentazon) Buctril (bromoxynil) Predict (norflurazon) Princep (simazine) Sencor (metribuzin) Simazat (simazine + atrazine) Cell Membrane Disruptors (Photosystem I) Gramoxone Max (paraquat) Cell Membrane Disruptors (PPO Inhibitors) Aim (carfentrazone) Authority, Spartan (sulfentrazone) Cobra, Phoenix (lactofen) Flexstar, Reflex (fomesafen) Resource (flumiclorac) Stellar (lactofen + flumiclorac) Ultra Blazer (acifluorfen) Valor (flumioxazin) Pigment Inhibitors (Isoprenoid Pathway) Balance PRO (isoxaflutole) Callisto (mesotrione) Command (clomazone) Seedling Root Growth Inhibitors (Cell Division Inhibitors) Prowl, Pendimax (pendimethalin) Treflan (trifluralin) LOW RISK of developing resistance: LOW RISK of developing resistance Amino Acid Synthesis Inhibitors (EPSPS Inhibitor) Roundup products, Touchdown, Buccaneer, Glyphomax, and others (glyphosate) Nitrogen Metabolism Inhibitors (Glutamine synthetase Inhibitor) Finale (glufosinate) Liberty (glufosinate) Growth Regulators (Synthetic Auxins) Banvel, Clarity (dicamba) Butoxone 175 (2,4-DB) Butyrac 200 (2,4-DB) Distinct (dicamba + diflufenzopyr) Oracle (dicamba) Sterling (dicamba) Seedling Shoot Growth Inhibitors (Multiple) Define (flufenacet) Degree, Harness, Surpass, Topnotch (acetochlor + safner) Dual, Parallel, Stalwart (metolachlor) Dual II Magnum, Cinch, Brawl II(S-metolachlor) Micro-tech (alachlor) Outlook (dimethenamid – P) Tillam (pebulate) Volley (acetolchlor) Devrinol (napropamide) Managing Fields With HerbicideResistant Weeds: Managing Fields With Herbicide Resistant Weeds Rotate to herbicides with differing modes of action within a growing season and year to year Use tank mixtures, prepackaged formulations, or sequential treatments with different mode of action Sanitation: DO NOT SPREAD WITH HARVESTING EQUIPMENT Managing Fields With HerbicideResistant Weeds: Managing Fields With Herbicide Resistant Weeds Scout fields regularly. Identify non-controlled weeds Select herbicide based on weeds present in the field. Use only as necessary. Resistant Weeds: Resistant Weeds Future?? Change in grower outlook and method of weed management may be needed; Likely will occur only with a massive resistant weed across a region Slide36: Southern Weed Science Society 2007 Annual Meeting January 22-24 Opryland Hotel, Nashville TN
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