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Causes and Management of Insect and Mite Resistance in Strawberry Production1
James F. Price, Elzie McCord, Jr., and Curtis Nagle2Resistance of arthropods to crop management chemicals has been problematic since the early era of synthetic organic pesticides. During the late 1990s, the twospotted spider mite (Tetranychus urticae Koch) became resistant to abamectin, the miticide used in strawberry culture. Since then, several new miticides including acequinocyl, bifenazate, etoxazole, hexythiazox, and spiromesifen have been integrated into strawberry production, overuse of the abamectin has ceased, and it once again is effective in rotation with the new materials. This latter development could prove temporary, especially if growers again use abamectin regularly.
Poor performance of pesticides does not always indicate pest resistance. Such factors as pesticide degradation in storage, hydrolysis in acid or alkaline preparations, applications to an incorrect life stage, or other inadequate application procedures may contribute to poor control.
A Definition of Resistance
Pest populations can be susceptible or resistant to a pesticide. Resistance occurs when a formerly susceptible pest population becomes significantly less susceptible to a pesticide and degradation of the pesticide or improper application is not a factor. Pesticide resistance is a population-based phenomenon in which the genetic composition shifts and the population becomes dominated by individuals possessing genes that confer resistance.Establishment of Resistance
Resistant populations are protected from formerly effective pesticides through one or more means. For example, resistant pests may: (1) deactivate (break down), (2) sequester (safely store within their bodies), (3) avoid, or (4) excrete the toxin from their bodies more effectively, (5) have an altered target site that will not accumulate the toxin, or (6) reduce the permeability by the toxin through their exoskeletons ("shells").Individuals within a susceptible pest population often vary in their level of susceptibility; however, the non-susceptible type occurs only very rarely. When a pesticide is applied repeatedly, the susceptible pests die and the resistant ones survive, mate with other survivors and reproduce. Some of their offspring inherit the parents' characteristic for survival. Upon additional applications, the susceptible offspring within the remaining population die and the resistant ones survive, mate with other survivors and produce more offspring. Further applications additionally select for the resistant individuals until that form (genotype) is common. The population then is regarded as resistant and the effectiveness of the pesticide is lost.
Resistance Management
Resistance can develop rapidly with pests that have many generations per year, when multiple generations are exposed to a pesticide, and when new individuals do not move into a treated area to dilute the frequency of the resistant genes. Some of these factors occurred on strawberry farms in the 1990s, contributing to development of abamectin resistance in spider mites.The main objectives of on-farm resistance management programs should be to minimize the number of exposures of pests to pesticides with a similar mode of action and to use non-chemical approaches to arthropod management. (Mode of action is the specific activity of the toxin that results in the death of the pest. For instance, one mode of action is to inhibit mitochondrial complex I electron transport. This causes a failure of the pest to produce energy in affected cells and to die.)
Repeated exposures to a pesticide are the primary drivers of resistance but much can be done to manage pests by means other than chemicals. Care can be taken to rotate strawberries with other crops, use pest resistant varieties, plant pest-free transplants, conserve and release natural enemies, etc. Pest-specific tactics are available for particular situations such as removal of all ripe strawberries from the field to eliminate reproductive sites for sap beetles.
Strawberry fields should be scouted weekly and pesticide applications made only when pest densities approach economic injury levels. When pesticide use is required, products should be rotated among the different modes of action indicated on many modern product labels. A list of modes of action can be found by selecting "MoA Classification Scheme" at the Insecticide Resistance Action Committee Website: http://www.irac-online.org/Crop_Protection/MoA. asp .
Tables 1-3 present insecticide and miticide modes of action summaries for Florida strawberry production. Sound rotation plans often recommend pesticides of one mode of action for one pest generation and a pesticide of a different mode of action for another generation. If multiple pesticide applications are required, rotations should continue through all practical modes of action before returning to a previously used one. The use of certain unique products with known general modes of action (such as soaps and oils) is unlikely to result in pest resistance and no codes are assigned. These can be used without regard to a rotation plan for resistance management.
When pesticides are used, it is important to assure that fresh, fully potent pesticides are prepared and applied in accordance with label directions. Aqueous pesticidal preparations should be adjusted to near neutral pH (pH 7.0) or as specified by the label. Sprayer calibration, nozzle condition and pressure, and spray placement must be correct. Applications also should be timed and directed to contact the most susceptible life stage of the pest.
Conclusion
Episodes of pest resistance to popular pesticides can cause yield losses, reduction of fruit quality, added control costs, environmental degradation, and emotional stress among farmers. These consequences can be alleviated if resistance management is practiced throughout the strawberry industry. If growers minimize pesticide application by depending more on biological and cultural pest control measures, and reduce pest exposure to pesticides with identical modes of action, then resistance can become a rare phenomenon.
Tables
Table 1. Mode of action of insecticides and miticides registered for use in Florida's strawberry crops (presented by active ingredient). (Insecticide Resistance Action Committee (IRAC) mode of action classification codes version 5.3).
Active Ingredient (common name)
Trade Name Examples
Mode of Action Code
abamectin
Agri-Mek Abacus
6
acequinocyl Kanemite
20B
azadirachtin Aza-Direct Azatrol
18B
Bacillus thuringiensis aizawai
Agree Xentari
11B1
Bacillus thuringiensis kurstaki
Dipel Javelin
11B2
Beauveria bassiana
Botanigard Naturalis
bifenazate Acramite
25
bifenthrin Brigade
3
carbaryl Sevin 1A
chlorpyrifos Govern Lorsban
1B
diazinon
Diazinon 1B
endosulfan Thiodan Thionex
2A
etoxazole Zeal
10B
fenbutatin-oxide
Vendex
12B
fenpropathrin Danitol
3
hexythiazox Savey 10A
imidacloprid Admire Provado
4A
malathion Malathion 1B
methoxyfenozide
Intrepid
18A
naled Dibrom 1B
potassium salts of fatty acids AllPro Insecticidal Soap M-Pede
propargite Omite
12C
piperonyl butoxide
Pyrenone Pyreth-It
27A
pyrethrin
Pyrenone Pyreth-It
PyGanic
Pyrellin
3
pyriproxyfen Esteem
7D
rotenone Pyrellin
21
s-methoprene Extinguish 7A
spinosad Entrust Justice
Spintor
5
spiromesifen Oberon
23
thiamethoxam
Actara Platinum
4A
Table 2. Mode of action of insecticides and miticides registered for use in Florida's strawberry crops (presented by mode of action code). (Insecticide Resistance Action Committee mode of action classification code version 5.3).
Mode of Action Code
Active Ingredient (common name)
Trade Name Examples
Beauveria bassiana
Botanigard Naturalis
potassium salts of fatty acids AllPro Insecticidal Soap M-Pede
1A
carbaryl Sevin 1B
chlorpyrifos Govern Lorsban
diazinon Diazinon malathion Malathion naled Dibrom 2A
endosulfan Thiodan Thionex
3
bifenthrin Brigade
fenpropathrin Danitol
pyrethrin Pyrenone PyGanic
Pyrellin
Pyreth-It
4A
imidacloprid Admire Provado
thiamethoxam Actara Platinum
5
spinosad Entrust Justice
Spintor
6
abamectin Abacus Agri-Mek
7A
s-methoprene Extinguish 7D
pyriproxyfen Esteem
10A
hexythiazox Savey
10B
etoxazole Zeal
11B1
Bacillus thuringiensis aizawai
Agree Xentari
11B2
Bacillus thuringiensis kurstaki
Dipel Javelin
12B
fenbutatin-oxide
Vendex
12C
propargite Omite
18A
methoxyfenozide
Intrepid
18B
azadirachtin Aza-Direct Azatrol
20B
acequinocyl Kanemite
21
rotenone Pyrellin
23
spriomesifen Oberon
25
bifenazate Acramite
27A
piperonyl butoxide Pyrenone Pyreth-It
Table 3. Mode of action of insecticides and miticides registered for use in Florida's strawberry crops (presented by trade name). (Insecticide Resistance Action Committee mode of action classification codes version 5.3).
Trade Name Examples
Active Ingredient (common name)
Mode of Action Code
Abacus
abamectin
6
Acramite
bifenazate
25
Actara
thiamethoxam
4A
Admire
imidacloprid
4A
Agree
Bacillus thuringiensis aizawai
11B1
Agri-Mek
abamectin
6
AllPro Insecticidal Soap potassium salts of fatty acids Aza-Direct azadirachtin 18B
Azatrol
azadirachtin
18B
Botanigard Beauveria bassiana
Brigade
bifenthrin
3
Danitol
fenpropathrin
3
Dipel Bacillus thuringiensis Kurstaki
11B2
Diazinon diazinon 1B
Dibrom naled 1B
Entrust spinosad
5
Esteem
pyriproxyfen
7D
Extinguish s-methoprene 7A
Govern
chlorpyrifos
1B
Intrepid
methoxyfenozide
18
Javelin Bacillus thuringiensis kurstaki
11B2
Justice
spinosad 5
Kanemite
acequinocyl
20B
Lorsban
chlorpyrifos
1B
M-Pede potassium salts of fatty acids Malathion malathion 1B
Naturalis Beauveria bassiana
Oberon
spiromesifen
23
Omite propargite 12C
Platinum
thiamethoxam
4A
Provado
imidacloprid
4A
PyGanic pyrethrin 3
Pyrellin pyrethrin & rotenone 3 & 21
Pyrenone pyrethrin & piperonyl butoxide 3 & 27A
Pyreth-It pyrethrin & piperonyl butoxide 3 & 27A
Savey
hexythiazox
10A
Sevin
carbaryl 1A
Spintor spinosad 5
Thiodan
endosulfan
2A
Thionex
endosulfan
2A
Vendex
fentutatin-oxide
12B
Xentari
Bacillus thuringiensis aizawai
11B1
Zeal
extoxazole
10B
Footnotes
1. This document is ENY-841 (IN713), a publication of the Department of Entomology and Nematology, Florida Cooperative Extension Service, IFAS, University of Florida. Publication date: November 2007. Please visit the EDIS website at http://edis.ifas.ufl.edu.2. James F. Price, associate professor, Gulf Coast Research and Education Center; Elzie McCord, Jr., associate professor, Dept. of Biological Sciences, New College of Florida; and Curtis Nagle, biological scientist, Gulf Coast Research and Education Center. Cooperative Extension Service, IFAS, University of Florida, Gainesville, FL 32611
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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
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