Bean Late last week, Rod Grusey (Hardin Co KY ANR agent) reported a significant soybean stem borer infestation in a 60 acre LaRue county field (planted May 15).

Live borers were found in 80% to 90% of the stems examined, about 10% of the plants were lodged. Infested stems also were found in several other fields in the area. There have been a few reports of the insect from west Kentucky this season but we don’t often see significant infestations in the central portion of the state.

Most of the losses to this insect come from lodged plants, not physiological yield loss from the stem tunneling. Early-planted fields have the highest potential for infestation. Check and harvest them first if significant infestations are found. Look for lodged bean plants that are broken off smoothly near the soil line. The two opposing surfaces of the break (upper face of root end and lower face of stem end) will be smooth and often closed (no visible tunnel). Split lodged stalks and look for the borer in the root end, and a tunnel packed with frass (sawdust-like insect waste) in the upper section. Either sign is diagnostic of the pest.

The larva of the soybean stem borer, Dectes texanus texanus, is legless and has a small, brown head. Its long creamy white body is about 5/8-inch long with distinct, accordion-like ridges. Following egg hatch earlier in the summer, the larva feeds in the leaf petiole, then tunnels into the main stem. During the summer, it chews its way up and down inside the main stem. By September, it arrives at the base of them stem and forms an overwintering cell. Ragweed, cocklebur, and other weeds also are suitable hosts for this insect.

For more information about soybean pests, visit Insect Management Recommendations.

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