3 Quick Tips: Managing Pesticide Resistance

Columns - Trends

June 9, 2011

Julie Newman

Pesticide resistance can occur with repetitive use of the same chemicals. A resistance management plan is critical to avoiding pesticide resistance and to sustaining the use of limited available products. Here are some tips to consider when developing a resistance management plan.

Quick Tip 1
Minimize pesticide use. Reduce pesticide use by scouting crops regularly and applying pesticides only when pests are present at threshold levels, targeting the most susceptible life stages. Incorporate non-chemical strategies such as installing exclusion screening, altering the environment to control foliar pathogens and incorporating biological controls.

Quick Tip 2
Know chemical mode of action. Resistance management strategies include rotating pesticides with the same mode of action or group number. It is therefore important to know the mode of action for the active ingredient of each pesticide that you use. The mode of action can be found on the pesticide label and on the Useful Websites listed at the end of this article.

The mode of action is the mechanism by which the pesticide kills the pest and is different than the chemical class. Rotation schedules should not be based only on the chemical class because these pesticides may have the same mode of action. For example, organophosphates and carbamates, despite being different chemical classes have identical modes of action (interfering with the nervous system of the target insect).

Quick Tip 3

Look for pesticide properties that do not promote resistance. Avoid the use of persistent chemicals. An ideal pesticide quickly dissipates so that pesticide residuals do not degrade over time to a concentration that will kill only the susceptible individuals within a population. When persistent chemicals must be used, consider where they can be used in a rotation scheme to provide the control needed and with a minimum length of exposure.

Products with multiple modes of activity can be used anytime in a rotation scheme. These include pesticides that kill by desiccation or smothering (insecticidal soap, horticultural oils), selective feeding inhibitors and biopesticides.

In contrast, conventional insecticides and miticides tend to have site-specific modes of activity. These pesticides inhibit one vital function or target site. Also, these pesticides must be managed carefully because it only takes a single-gene mutation to develop resistance.

Pesticides can be selective or nonselective (broad-spectrum). Selective pesticides kill only certain groups or species of plants or animals and are generally preferred in IPM programs. Use of selective pesticides in combination with biological control fosters reduced pesticide use and avoids the buildup of pesticide resistance among pest survivors through parasitism or predation.

Check fungicide labels and group information for the risk of resistance development. Know which fungicides are rated as high risk and follow label instructions for managing fungicide resistance. Most of the newer fungicides have a single-site mode of action which favors the development of resistance.

Look for fungicides that are multi-site inhibitors (mode-of-action group M), denoting a low risk of resistance development. Include these multi-site inhibitors in your rotation schedule.

Have a question? You can write Julie at jpnewman@ucdavis.edu.