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Agronomic Crops Network

Ohio State University Extension


Keep an Eye on the Horizon for Dry Weather Insect Pests

While nobody knows what the future holds regarding weather, recent dry conditions have made people think about the potential for drought this summer.  In field crops, certain insect pests tend to be worse under dry conditions – either because hot and/or dry weather favors their biology, reduces the impact of natural enemies that help control them [particularly insect-killing fungi], weakens the plants’ resistance to the insects or increases the physiological damage potential, or some combination of these factors.  While you can’t control the weather, stepping up scouting efforts in drought conditions can help you control unexpected damage from these dry-weather insects.

In soybean, spider mites, and grasshoppers are commonly worse in drought.  In corn, grasshoppers can increase but are unlikely to be numerous enough to affect yield; however, spider mites can be a problem.  In alfalfa, potato leafhopper damage can be worse under dry conditions, largely because the plants are more prone to “hopper burn” when they are stressed.

A very important fact about spider mites is that many commonly used insecticides in the pyrethroid category [such as lambda-cyhalothrin (for example, Warrior) and esfenvalerate (for example, Asana)] are known to flare spider mite populations rather than control them [one exception is the pyrethroid active ingredient bifenthrin].  So under drought conditions, it is very important not to use such products either as tank-mixed insurance treatments (which can create a problem where there was none) or for mite control.  For mite management, you will usually get the best results with a miticide product, such as abimectin (for example, Agri-Mek) in soybean and etoxazole (for example, Zeal) in corn and soy.  These are typically more expensive but they are worth the extra cost if spider mites are a real problem.

For a comprehensive list of products labeled in different field crops, their active ingredients, and scouting/threshold guidance, download the Michigan/Ohio State Field Crop Insect Pest Management Guide at

What can you do right now?  Be aware that in dry conditions early scouting efforts for these pests can pay off.  Also, if much of the Midwest is affected by drought this summer, miticides may be hard to come by later – if these are products you want to have on hand, plan accordingly.  And stay tuned to the C.O.R.N. newsletter for more scouting and management information on emerging field crop pests.

*Our use of certain product names is not a brand endorsement, but provided for examples of products containing certain active ingredients.

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.