Soybean Insects

Dectes Stem Borer, Dectes texanus.


These elongated, long-antennaed gray beetles grow to be 3/8 to 1/2 inches long. Eggs are laid in leaf petioles, usually in midcanopy. Larvae tunnel down the petiole and into the stem, generally moving downward. Tunneling in the petiole causes the entire leaf to wilt and die. Dead, wilted and drying leaves above the normal senescence zone at the bottom of the plant can help identify stem borer infestations.

By the time the plants reach physiological maturity, the larva will have tunneled to the base of the plant. Larvae frequently girdle the plant internally, which weakens stems so they break. Larvae overwinter in the stem bases, plugging the hollowed section near the girdling point so the stem base appears solid. The larvae are cannibalistic, so only one insect is present within each infested plant late in the year.

Windy conditions cause girdled-plants to lodge, causing significant harvesting problems and yield losses. Serious damage has been most common in south central Kansas, but it is becoming increasingly common in north central and western Kansas.

No resistant varieties have been identified for this pest. Since adult beetles emerge over several weeks, multiple insecticide applications would be needed to significantly reduce larval infestations and would not be economically justified.

Crop rotation and timely harvesting have been suggested as beneficial management strategies. Unfortunately, in areas where soybeans are commonly grown and beetle populations are high, crop rotation is of limited value. In addition, this pest can also infest sunflowers which can complicate management when both crops are produced in the same area. Fields should be sampled before maturity for the presence of stem borer tunneling and live larvae by carefully splitting stems from several locations throughout the field. Fields with high percentages of infested stems should be harvested as soon as possible to avoid girdling and lodging.

More detailed information on the biology of this pest is available in the KSRE publication MF-2581: The Dectes Stem Borer .

Additional resources:

Soybean Stem Borer Life Cycle in Pictures

Soybean Stem Borer Distribution History

Soybean Stem Borer Research

Page last updated 11/01/2013 by J.P. Michaud.