Hot, Dry Conditions Could Invite Two-Spotted Spider Mite

June 18, 2007

WOOSTER, Ohio -- Ohio's abnormally dry to moderate drought conditions could set the stage for potential problems from a pest that thrives under such an environment.

Ron Hammond, an Ohio State University Extension entomologist with the Ohio Agricultural Research and Development Center, said that soybean growers should be keeping their eye on the two-spotted spider mite.

Historically, the sapsucker is a late-season pest and not normally a significant problem throughout the Midwest. However, given the current state of Ohio's weather, the insect could show up earlier than anticipated.

"The two-spotted spider mite is a problem under hot, dry conditions where the plant is under a lot of stress. A good portion of Ohio is under those conditions right now with no significant rainfall in the forecast," said Hammond. "Growers in dry areas could potentially be facing problems, so they should start paying more attention to their fields."

The two-spotted spider mite, an arthropod with a black spot on each side of its white or red body, is too small to see without a hand lens, so keeping track of economic thresholds is difficult. However, mite injury on soybean plants is easily recognizable.

"Mite feeding produces a very characteristic yellow speckling on the top portion of the soybean leaves," said Hammond.

As mites rapidly multiply and plants become heavily infested, the 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.

"By the time the leaves turn bronze, yield is already lost," said Hammond.

Untreated soybean fields can experience as high as 47-percent yield loss, based on OARDC research.

"If growers begin seeing pockets of this speckling throughout a field, then treatment might be needed," said Hammond. "With early-season spider mite outbreaks, infestations tend to occur throughout the field rather than just along the field edges, characteristic of late-season outbreaks. This will make scouting more challenging."

The following scheme for evaluating the presence and damage of two-spotted spider mite, used during the drought of 1988, may aid growers when scouting their fields:

• Mites are barely detected at field perimeter. Multiple plants need to be inspected before mites are found. Assessment: non-economic.

• Presence of mites is easy to detect at field perimeter and dry spots, but difficult to detect within the field. Foliage is still green but feeding injury with few mites under lower side of leaves is detectable, but not on every plant. Assessment: Non-economic, but warrants monitoring.

• Entire field exhibits some sign of infestation with speckling and some discoloration of the lower leaves. Foliage exhibits various levels of feeding injury on relatively healthy foliage. Field perimeter and dry spots exhibit severely damaged plants. Assessment: Treatment warranted, especially if immature mites are in abundance.

• Infestation is widespread with discolored and wilting foliage easily detected throughout the field. All plants are heavily infested when examined closely, and severe damage is evident. Assessment: Effective treatment may save the field.

• Total field discoloration and drying down of foliage is present. Significant foliage and stand loss is evident. Assessment: Field may be beyond the point of recovery. However, new growth may resume if treated.

For updates regarding any developments of the two-spotted spider mite, refer to the Ohio State University Agronomic Crops Team Web site at http://agcrops.osu.edu.

Author(s): 
Candace Pollock
Source(s): 
Ron Hammond