3 Quick Tips: Managing Pesticide Resistance

In the June issue of Greenhouse Management (Page 54), I discussed the importance of developing a pesticide resistance plan that minimizes pesticide use. Understanding pesticide properties and mode of action is integral to the process of selecting pesticides to minimize pesticide resistance. A pesticide resistance plan should also incorporate pesticide application strategies that help to reduce pesticide resistance. Here are three pesticide application tips to consider when managing pesticide resistance.
 

Quick Tip 1
Follow rotation strategies appropriate for the specific type of pest. Resistance management strategies for insects and other arthropod pests, weeds and pathogens all include rotating pesticides that have the same mode of action. However, rotation strategies differ for specific types of pests. For example, it is suggested that fungicides from different modes of action be rotated with every application when managing fungal pathogens.

On the other hand, the general guideline for managing insect pests is to rotate the insecticide to one with a different mode of action with each insect generation. Long-term rotation through many chemical modes of action in successive insect generations helps maintain pesticide efficacy. Using a specific mode of action for longer than the single generation time of the insect pest increases the chance of resistance. The survivors of the first generation and the next will most likely be tolerant to that mode of action.

Conversely, if insecticides are switched with every application, the same individual insects could be exposed to a mix of chemicals and a pest population that is resistant to pesticides with multiple modes of action could develop. Remember that insect generation time from egg to adult is dependent on temperature. Thus, the pesticide rotation cycle is shorter during warm conditions and longer during cool conditions.

Always refer to the pesticide product labels, which may have specific resistance management instructions. The label may also limit the total number of applications per year or have other use restrictions.
 

Quick Tip 2
Avoid tank mixes of insecticides/miticides. Tank mixes of fungicides can be used to effectively manage resistance, but tank mixes of insecticides/miticides are not recommended. Combining two pesticides with the same mode of action in a tank mix increases the likelihood that resistant pest individuals will establish.

Although tank mixing or combining insecticides/miticides with different modes of action may delay resistance and sometimes provides superior control, long-term use of these pesticide mixes can also lead to pesticide resistance if resistance mechanisms to each pesticide arises together in some of the pests. Continued use of the mixes will select for multiple-pesticide-resistant pests. Similarly, continued use of commercial products that contain pesticide combinations with two modes of activity may result in resistance to both modes of activity.

In specific situations, the simultaneous application of two different types of chemicals may be necessary, such as when there are mixed life stages of a pest. However, even then, tank mixes should be avoided. For example, rather than tank mixing an insect growth regulator to control immature stages of an insect pest with an adulticide, two formulations should be selected that require different types of application. For instance, if an insect growth regulator is applied as a spray, the adulticide could be applied as an aerosol or smoke to provide rapid kill of the adults and little residual that might select for resistance buildup in surviving immature stages.
 

Quick Tip 3
Maintain records of pesticide performance and assess pesticide coverage. Following the pesticide application, use pesticide records to identify less effective products. If there is only one chemical that is effective against a pest and other available products are only marginally effective, use the marginally effective materials when pest pressure is less severe and reserve the effective material for more critical situations.

If a pesticide that is touted to be effective is not working, do not assume that you have a pesticide resistance problem. It could be that the pesticide is not actually contacting the targeted pest.

Make sure you are using appropriate nozzle sizes and spray pressure, and ensure that application equipment is properly calibrated. Thoroughness of spray pattern can be assessed by placing water-sensitive paper in upper-, mid- and lower-plant canopy locations. You may need to add an adjuvant to better spread, stick or penetrate the plant material and provide more uniform coverage for more effective pest control.

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