Larvae of the longhorn beetle, Dectes texanus, bore in sunflower stems and often girdle the plant at the end of the season. The adult is a bluish gray beetle about 3/8 inches (7 to 10 millimeters) with long black and gray banded antennae. They lay their eggs in the petioles of lower leaves and the young larvae tunnel the petioles until they reach the main stem. Mature larvae are creamy white, legless, corrugated, and tapered to the rear. Mature larvae girdle the inside of the stalk to create a chamber at the base of the stalk where they overwinter. This insect also is known as the soybean stem borer and is a pest of soybeans in southern and central US productions areas. It also feeds on several weedy hosts, including cocklebur and ragweed.
Girdling can result in lodged plants that cannot be harvested. Yield is not affected if plants can be harvested.
Emphasize losses due to lodging. Reduce plant populations to encourage thicker, more lodging-resistant stems. Assess infestations before harvest and harvest the most infested fields first to reduce the opportunity for lodging.
Categories: Sunflower, Insects, Longhorn beetle
Date: 8/5/2005