The prolonged extreme heat and rainfall shortages that have led to moderate and severe drought conditions across Ohio also have led to reports of two-spotted spider mite – a pest that can cause severe soybean damage or death. Many growers have already reported finding two-spotted spider mites on soybeans, says Ron Hammond, an Ohio State University Extension entomologist who also has an appointment with the Ohio Agricultural Research and Development Center.

Spider mites, which feed on the underside of the foliage with sucking mouth parts and can be destructive when abundant, thrive on plants that are under stress, especially in hot, dry field conditions.

This is significant, considering that all of Ohio except for small portions of four counties near the West Virginia border is experiencing moderate drought, with areas near the Indiana and Michigan borders experiencing severe drought as of July 24, according to the most recent U.S. Drought Monitor.

"Numerous areas in the drier areas of Ohio are already seeing them, and some fields are already being sprayed," Hammond says. "Mites are showing up not only on field edges but also within the field.

"Two-spotted spider mites have the potential to cause more yield loss than any other insect, with the damage caused by the mites being severe enough to kill the entire plant. Growers who have a bad infestation will not see any yield from the affected area."

Typically, Ohio soybeans are affected by two-spotted spider mites in July or early August, because moisture levels earlier in the year are usually high enough to keep the pests at bay, Hammond says.

But the early hot, dry conditions and low soil moisture levels have caused the pests to appear earlier and, because many soybean plants are stressed, the pests have more potential to impact entire fields instead of just the edges, Hammond says.

"If we were having normal rainfall, we wouldn't be worried about mites right now," he says. "In some parts of the state, soils are very dry and crops are starting to suffer."

Currently, topsoil moisture was rated 53% very short, 37% short and 10% adequate, with no surplus, according to the latest USDA weekly crop report.

Hammond says growers should begin scouting their fields for two-spotted spider mites now. Spider mite infestations can first be noticed by yellow stippling on the upper surface of the leaves, he says. The mites themselves, which are found on the underside of the leaves, can be identified using a good hand lens.

"In making an assessment of a spider mite-infested field, it is important that one recognizes the early sign of mite feeding, which is the stippling or speckled effect that initially appears on the foliage when foliage is still green," he says.