Post on 11-Aug-2020
transcript
The Basics of Pesticide Resistance
Dr. Fred Fishel, Professor – UF/IFAS Agronomy
When Pesticides Don’t Work
• Improper pest identification
• Incorrect pesticide dosage
• Improper application timing
• Pesticide doesn’t reach target pest
• Unfavorable environmental conditions
• State of poor pesticide conditions
• Pesticide resistance
Terminology
• Resistant: Pest was originally susceptible to pesticide; over time control lost through the selection of resistant individuals.
• Tolerant: The inherent ability of a species to survive following a pesticide treatment – was never susceptible.
Terminology
• Mode of action: describes the biochemical processes by which the pesticide poisons the pest (for example, disrupting photosynthesis).
• Target site of action (mechanism of action): the exact location of inhibition, such as interfering with the activity of a specific enzyme within a metabolic pathway.
Terminology
• Cross resistance: resistance to 2 or more pesticides that share the same mode of action.
– Dotted duckweed (Landoltia punctata)
– Diquat and paraquat (WSSA Group 22)
• Multiple resistance: resistance to 2 or more pesticides with different modes of action.
– Palmer amaranth (Amaranthus palmeri)
– Imazapic and glyphosate (WSSA Groups 2 and 9)
Resistance in General
“Biotype”
“The Pesticide Treadmill”
1. Pest population rises
2. Apply pesticides
3. Pests develop resistance
4. Apply more pesticides
5. Resistance becomes more prevalent
6. Switch to new pesticide (if possible)
History of Resistance (Organic Pesticides)
• 1947 – insecticides
– Housefly
– Organochlorines (DDT)
– Organochlorines have long since been banned for use
• 1960s – fungicides
– Powdery mildew
– Benzimidazoles (benomyl)
– DuPont voluntarily canceled benomyl due to high legal costs
History of Resistance (Herbicides)
• 1957 – weeds
– 2,4-D resistant dayflower in sugarcane field
Herbicide Resistance Mechanisms
Sequestered in vacuole
X Z
X
Help! Get me outta
here!
X Y
X
Please! Let me in!
I can’t do my
job!
X
X
My key won’t
fit!
More than 450 resistant biotypes globally
9 of the top 15 most common herbicides prone to resistance are ALS inhibitors
Herbicide Resistance in Florida
Year Species Situation Herbicide(s)
1985 American black nightshadeTomato Paraquat
1996 GoosegrassDiquat, paraquat2001 Dotted duckweed
Aquatic2002 Hydrilla Fluridone
2008
Palmer amaranth Cropland
Imazapic, pyrithiobac-Na
2013Glyphosate
Glyphosate, imazapic
2014 Ragweed parthenium Industrial Glyphosate
Resistance Concerns
Circa mid-1990’sBecause glyphosate is non-selective, Monsanto has insisted that glyphosate resistant weeds will not appear with the use of this herbicide. With the imminent release of glyphosate resistant corn and soybeans, this hypothesis will soon be tested on potentially millions of acres. Resistant weed populations have been reported already in locations outside the USA.
Managing Resistance in General
• Rotate herbicide applications using different modes of action
• Use tank- or pre-mixes of different MOAs
• Avoid unneeded applications
• Follow label rates
• Use non-herbicidal alternatives if possible
• Monitor changes in weed control results
Playing by the Numbers
Spraying by the Numbers
• Weed Science Society of America herbicide classification system
– Approximately 30 herbicide modes of action identified
Spraying by the Numbers
Aquatic Herbicide Mode of Action Group Numbers According to the WSSA
WSSA group number Common name Mechanism of action
2Bispyribac-sodium,Imazapyr, Imazamox, Penoxsulam
Enzyme inhibitor (ALS)
4 2,4-D, Triclopyr Growth regulator (organo-auxin)
9 Glyphosate Enzyme inhibitor (EPSPS)
12 FluridonePhotosynthesis inhibitor (pigment synthesis – PDS)
14Carfentrazone, Flumioxazin
Enzyme inhibitor (PPO)
22 Diquat Photosynthesis inhibitor
27 TopramezonePhotosynthesis inhibitor (pigment synthesis – HPPD)
NCEndothall, Hydrogen peroxide, Copper
Photosynthesis inhibitor (and other effects)
Spraying by the Numbers
Thank you for your
attention!