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Herbicide Resistance: Evolution, Prevention and Control

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Presentation on theme: "Herbicide Resistance: Evolution, Prevention and Control"— Presentation transcript:

1 Herbicide Resistance: Evolution, Prevention and Control
Jamshid Ashigh Extension Weed Specialist/ Assistant Professor

2 Chemical weed control Herbicides 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.

3 Herbicide resistance world wide

4 Herbicides development and use
The rate of introduction of new herbicides has slowed dramatically. Due to the high cost Ten multi-national corporations In 2004 there were four remaining There is a strong imperative to use the currently available herbicide resources in more sustainable ways. Sustainable agriculture IWM

5 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 (WSSA). Similar to resistance to: Insecticides Fungicides Antibiotics

6 Evolution of herbicide resistance
Weed populations are diverse Most individuals are susceptible to herbicides A few individuals are naturally resistant (1X10-8 to 1X10-10) After the herbicide is applied they are the only ones to survive

7 Evolution of Herbicide resistance
Survivors put seeds in the seed bank The following year A few more survivors Not noticeable Several years (3-10 years) of selection before it becomes visible 30% of the total population

8                                                                                                Resistance selection Source: J.L. Gunsolus. Herbicide Resistant Weeds North Central Region Extension Publication 468.

9 Major factors influencing the evolution of resistance
                                      Major factors influencing the evolution of resistance Selection pressure Initial frequency of herbicide-resistant individuals 1X10-8 to 1X10-10 Gene flow Pollen and seed movement Resistance controlled by single gene (e.g., ALS-inhibitors resistance)

10 Selection pressure Efficiency of the herbicide Frequency of use
Sensitive weeds Frequency of use Applied alone Duration of effect

11 Weed characteristics that influence the evolution of resistance
Annual life cycle Produce large numbers of seed Genetic variability Outcross

12 What makes the weeds resistant?
Altered site of action Change in target enzyme Enhanced metabolism Ability to degrade herbicide Decreased absorption and translocation Herbicide does not get to its site of action Sequestration Herbicide not available to the plant (stored in vacuoles)

13 Altered site of action Alterations in the site of action that prevent the herbicide from binding are the most common mechanism of resistance Caused by mutation(s) in the gene(s) Change in the amino acids

14 Triazine mechanism of action
Thylacoid membrane Chloroplast Source: Dr. J. Christopher Hall

15 Plastoquinone Binding
Source: Dr. J. Christopher Hall

16 Triazine Binding Source: Dr. J. Christopher Hall

17 Triazine Resistance Source: Dr. J. Christopher Hall

18 Confirmation 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.

19 Source: Dr. Earl Creech

20 Confirmation of resistance in the lab
Seedlings. Pre emergence Post emergence DNA sequencing. Absorption, translocation and metabolism S R R S Pre- emergence Post- emergence

21 Herbicide 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.

22 Glyphosate-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.

23 Glyphosate-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.

24 Preliminary Results Resistant Susceptible 2X 1X

25 It is important to adopt proactive weed management strategies to prevent/control resistance.

26 Prevention and management
Prevent seed production introduction Monitor the field Follow label direction Rotate herbicide Rotate crop Use less herbicide Integrate other methods of weed control with herbicides Use herbicide mixtures

27 Problem 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 followed Due to stacking of resistance genes Triazine resistance + ALS resistance

28 Criteria for good herbicide mixtures
Same residual (persistence) Same efficacy (control the same spectrum of weeds) Different mode of action

29 Example of a bad mixture
Herbicide Mode of action Residual Pursuit ALS Long Basagran Photosystem II None Follow label direction for mixture options

30 Label Legally binding Contains critical info: How to mix & apply
Restrictions Use rates Spill info/contact Soil activity Species Time of application Mixture options

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