edited by Dr. Frank J. Dainello, and produced by Extension Horticulture, Texas Cooperative Extension,
The Texas A&M University System, College Station, Texas.
Resistance Build-Up
This article by Vicky Boyd, Editor, appeared in the
April 2001 issue of “The Grower.”
In the less than three years since spinosad insecticide became commercially available, diamondback moth caterpillars in Hawaii have become resistant to the product. While pest control experts point to Hawaii’s unique growing environment as part of the reason for the rapid resistance development, they say it nonetheless shows the need for growers everywhere to adhere to strong resistance management principles, regardless of the product.How Does Resistance Develop?Those rules include strictly following label recommendations and rotating products with different modes of action, says Gary Thomspon, a Dow AgroSciences research and development manager and current chairman of the international Insecticide Resistance Action Committee (IRAC), an international group of insecticide registrants and insect experts.
“It’s possible that we could develop problems if we don’t implement good resistance management strategies with these three compounds,” says Stephen White, Syngenta insecticide technical-brand manager. He was referring to the relatively new chemistries of Proclaim (from Syngenta), Avaunt (from DuPont Agricultural Products), and Success and Spintor Naturalyte (spinosad products from Dow Agro Sciences).
Resistance develops after a few pests -- whether weeds, insects, or pathogens -- within the general population escape death by receiving a sublethal pesticide dose for a variety of reasons. Some of the individuals may be genetically predisposed to tolerate pesticides better than others. These tend to survive and increase disproportionately in the population relative to the more susceptible individuals over time, as long as the same pesticide is present.Minimize Resistance With Integrated ApproachThe resistant pests reproduce unchecked, and eventually a large percentage of the population is able to withstand treatment. The problem is worsened when growers use the same chemical or same family of chemistries repeatedly without rotation.
Typically, chemicals from different families use different control mechanisms which tend to challenge the pest, making it more difficult to overcome the treatment.
If use of a specific family of chemicals is discontinued, some pests may become more susceptible over time.
The ultimate strategy to avoid insecticide resistance is prevention. More and more crop specialists recommend insecticide-resistance management programs as one part of a larger integrated pest management (IPM) approach. The following recommendations were developed by IRAC to reduce the chances the pests in your field will develop resistance to insecticides.If Resistance Is Suspected
- Monitor Pests.
- Scouting is one of the key activities you can implement as part of their insecticide-resistance management strategy. Follow the progress of insect population development in your fields (with or without the assistance of a crop consultant or advisor) to determine if and when control measures are warranted.
- Focus On Economic Thresholds.
- Insecticides should be used only if insects are numerous enough to cause economic losses that exceed the cost of the insecticide plus applications. An exception might be in-furrow, at-planting treatments for early-season pests that usually reach damaging levels annually.
- Integrate Control Strategies.
- Monitoring is just one element of an insecticide-resistance management program. To avoid resistance, consider these major resistance management strategies.
- Take An Integrated Approach.
- Incorporate as many different control mechanisms as possible.
- Time Applications Correctly.
- Time insecticide and miticide applications against the most vulnerable life stage of the insect pest. Use spray rates and application intervals recommended by the manufacturer.
- Mix And Apply Carefully.
- As resistance increases, the margin for error in terms of insecticide dose, timing, coverage, etc., assumes even greater importance.
- Alternate Different Insecticide Classes.
- Avoid selecting for resistance or cross-resistance by repeated use, year after year, of the same insecticide or related products in the same class.
- Protect Beneficials.
- Select insecticides in a manner that causes minimum damage to populations of beneficial arthropods.
- Consider Crop Residue Options.
- Destroying crop residue can deprive insects of food and overwintering sites.
If you encounter control failure and suspect you have a case of insecticide resistance, don’t jump to conclusions until you consult with crop specialists. Several other problems have similar symptoms, so if poor control is experienced, growers should first check for:Be Certain It’s Resistance
- Application error;
- Equipment failure;
- Environmental conditions, such as weather.
If resistance is suspected, first and foremost, do not re-spray with an insecticide of the same chemical class. Contact the sales person to help evaluate the cause of control failure.To confirm resistance, an evaluation of the surviving insects for the level of detoxifying enzymes or the presence of resistant genes will be made by professionals using a number of methods. Always work with local crop specialists to determine appropriate monitoring and diagnostic programs for their resistance-related situations.