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Posted 30 August 2013. PMN Crop News.

As Fields Dry Out, Watch for Spider Mites

Source: United Soybean Board Press Release.

Chesterfield, Missouri (August 13, 2013)--Soybean farmers are advised to be on alert for spider mites, which tend to thrive during growing seasons that feature high temperatures and scarce rainfall.


While that might not describe current conditions throughout the soybean belt, experts point out that the situation can deteriorate quickly once fields that experienced a wet spring begin to dry out.

Complicating farmers’ search for spider mites is the fact that damage from the pest is often similar to the symptoms of drought stress in soybeans, says Ada Szczepaniec, an entomology specialist for South Dakota State University Extension. She notes that mite damage usually shows up as small yellow spots on soybean leaves. As the population grows and feeding escalates, the leaves turn from yellow to bronze and finally brown. Those leaves eventually drop off the plant.

“Spider mites feed on plants by piercing the plant tissue and sucking up contents of plant cells, causing characteristic stippling damage,” explains Szczepaniec.

To help farmers inspect their fields, Szczepaniec offered the following tips:

• A quick way to scout for mites is to tap potentially infested foliage over black construction paper and examine it with a 10X magnifying lens.

• Inspect at least 10 plants throughout the field, taking to account that spider mites live on the underside of soybean leaves. Make note of the proportion of leaves that are infested with spider mites on each plant, and record the percentage of leaf area on each infested leaf that is damaged by spider mites.

• Symptoms of spider mite damage to leaves include white-to-yellow spots on plant tissue where spider mites sucked out the contents of the plant’s cells.

• Extension specialists recommend treating if damage is visible in the lower third of the plant and spider mite colonies are visible in the middle third of the plant.

• Because pesticide applications do not kill spider mite eggs, scouting should be repeated after treatments.

Reports of spider mites in U.S. soybean fields have been limited so far in 2013. Last year’s drought, however, resulted in spider mite infestations across much of the country’s soybean range, according to a 2012 crop damage report by the U.S. Department of Agriculture.