Presentation on theme: "Herbicide Resistance: Evolution, Prevention and Control"— Presentation transcript:
1Herbicide Resistance: Evolution, Prevention and Control Jamshid AshighExtension Weed Specialist/ Assistant Professor
2Chemical weed controlHerbicides are the most efficient technology for large-scale weed control.The introduction of new herbicides to replace those herbicides failing due to resistance is essential for weed management.
4Herbicides development and use The rate of introduction of new herbicides has slowed dramatically.Due to the high costTen multi-national corporationsIn 2004 there were four remainingThere is a strong imperative to use the currently available herbicide resources in more sustainable ways.Sustainable agricultureIWM
5Herbicide ResistanceHerbicide 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 (WSSA).Similar to resistance to:InsecticidesFungicidesAntibiotics
6Evolution of herbicide resistance Weed populations are diverseMost individuals are susceptible to herbicidesA few individuals are naturally resistant (1X10-8 to 1X10-10)After the herbicide is applied they are the only ones to survive
7Evolution of Herbicide resistance Survivors put seeds in the seed bankThe following yearA few more survivorsNot noticeableSeveral years (3-10 years) of selection before it becomes visible30% of the total population
8Resistance selectionSource: J.L. Gunsolus. Herbicide Resistant Weeds North Central Region Extension Publication 468.
9Major factors influencing the evolution of resistance Major factors influencing the evolution of resistanceSelection pressureInitial frequency of herbicide-resistant individuals1X10-8 to 1X10-10Gene flowPollen and seed movementResistance controlled by single gene (e.g., ALS-inhibitors resistance)
10Selection pressure Efficiency of the herbicide Frequency of use Sensitive weedsFrequency of useApplied aloneDuration of effect
11Weed characteristics that influence the evolution of resistance Annual life cycleProduce large numbers of seedGenetic variabilityOutcross
12What makes the weeds resistant? Altered site of actionChange in target enzymeEnhanced metabolismAbility to degrade herbicideDecreased absorption and translocationHerbicide does not get to its site of actionSequestrationHerbicide not available to the plant (stored in vacuoles)
13Altered site of actionAlterations in the site of action that prevent the herbicide from binding are the most common mechanism of resistanceCaused by mutation(s) in the gene(s)Change in the amino acids
14Triazine mechanism of action ThylacoidmembraneChloroplastSource: Dr. J. Christopher Hall
15Plastoquinone Binding Source: Dr. J. Christopher Hall
17Triazine ResistanceSource: Dr. J. Christopher Hall
18Confirmation of resistance in the field Other causes of herbicide failure have been ruled out (e.g., plant size, time of application etc).The same herbicide or herbicides from the same family have been used year after year.One weed that is normally controlled is not controlled while other weeds are.Single weed species in patches and they are spreading.Mix of dead and healthy weeds from the same species are seen in the field.
20Confirmation of resistance in the lab Seedlings.Pre emergencePost emergenceDNA sequencing.Absorption, translocation and metabolismSRRSPre- emergencePost- emergence
21Herbicide resistant weeds Worldwide:323 Resistant Biotypes, 187 Species (112 dicots and 75 monocots)United States:Resistant weeds have been reported from 46 states.In New Mexico:One confirmed case (Kochia)Suspected glyphosate-resistant Palmer amaranth.Source: Dr. I. Heap.
22Glyphosate-resistance Glyphosate-resistant (Roundup ready) crops are the most widely used transgenic crops.98% of cotton in US.Glyphosate is also used extensively in other crops.Nine weed species including Palmer amaranth have developed resistance to Glyphosate.Resistance is threatening the ongoing sustainability of Glyphosate.
23Glyphosate-resistant palmer amaranth Glyphosate-resistant Palmer amaranth in Georgia, Tennessee, North Carolina, South Carolina and Arkansas.In late 2007, a Palmer amaranth population was reported to have survived Glyphosate applications in New Mexico.Palmer amaranth is an out-crossing plant:Spread faster than self-pollinated species.
25It is important to adopt proactive weed management strategies to prevent/control resistance.
26Prevention and management Prevent seed production introductionMonitor the fieldFollow label directionRotate herbicideRotate cropUse less herbicideIntegrate other methods of weed control with herbicidesUse herbicide mixtures
27Problem with rotating herbicides Herbicide rotation has not precluded the development of some types of resistance (e.g., multiple- or cross-resistant wild oat in Canada).Especially if the label rates are not followedDue to stacking of resistance genesTriazine resistance + ALS resistance
28Criteria for good herbicide mixtures Same residual (persistence)Same efficacy (control the same spectrum of weeds)Different mode of action
29Example of a bad mixture HerbicideMode of actionResidualPursuitALSLongBasagranPhotosystem IINoneFollow label direction for mixture options
30Label Legally binding Contains critical info: How to mix & apply RestrictionsUse ratesSpill info/contactSoil activitySpeciesTime of applicationMixture options