Is the Pump Primed for Spider Mites in Soybeans?

by: Bruce Clevenger

Adult twospotted spider mites (TSSM) are very small (ca. 1/60 inch in length), eight-legged arthropods (nymphs have 6 legs) with a black spot on each side of their bodies. Color of the mites is variable ranging from white to light red. The eggs of the mites appear like small, clear or pale marbles when viewed through a good hand lens. TSSM feed on the underside of the foliage with sucking moth parts and may be very destructive when abundant. Under hot and dry field conditions favorable to mites, the TSSM thrives on plants that are under stress. The juices that the mites obtain from stressed plants are rich in nutrients and the mites multiply rapidly. Soybean foliage infested with spider mites initially exhibits a speckled appearance. As plants become heavily infested, foliage turns yellow, then bronze, and finally the leaves drop off the plants as the effect of heavy feeding leads to dehydration and death of the plant.  As of July 2, 2012, TSSM have not been seen in abundance across NW Ohio in field edges or whole fields.

Economic thresholds based on the number of mites per plant have not been established for TSSM on soybeans. However, a scheme for evaluating an infested field based on observations of the presence of mite and feeding injury has been developed.  Close monitoring of individual fields will be critical during the next few weeks.  Don’t assume one field represents a greater area or all of a growers soybean production.  Populations of TSSM may begin spotting and require follow-up scouting.

Scouting procedures can be found at: http://ohioline.osu.edu/ent-fact/pdf/0024.pdf

Pesticide recommendations: http://entomology.osu.edu/ag/images/545%281%29.pdf

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