July 11, 2012

We are getting further reports of spider mites developing on field corn in southeast Nebraska. Continued hot, dry weather will encourage further development of spider mites.

The threshold table in our NebGuide, Spider Mite Mangement in Corn and Soybeans (G1167), needs to be updated to reflect current corn value. The table stops at $700/acre value ($/bu x bu/acre yield potential).

This table is based on research from Texas A&M University. In the current Texas A&M Extension publication E-400, Managing Insect and Mite Pests of Texas Corn, they suggest the following:

For market values that exceed $700 per acre, use the following formulas to determine an economic injury level.

1. For percent infested leaves the formula is (cost of control x 600) ÷ (price per bushel x bushel yield).
2. For percent of leaf area damaged the formula is (cost of control x 312) ÷ (price per bushel x bushel yield).

Colorado State University suggests: “The simple guideline is to treat if damage is visible in the lower third of the plant, and mite colonies are present in the middle third."

Once the crop has reached the hard-dough stage, no economic benefit will result from the treatment.

Mites in Soybeans

Spider mites have been reported in soybeans in isolated fields in southeast and northeast Nebraska.  Conditions in all of Nebraska are conducive to spider mite infestations and continued scouting is recommended for soybeans across the state. In many cases slowing the rate of population increase may be all that can be accomplished, unless we see good rains.

Also see the June 14 CropWatch article, Twospotted Spider Mites Early, Already in Southeast Nebraska Soybeans for factors affecting populations this year and treatment information.

Robert Wright
Extension Entomologist