|Corn Rootworm: Diabrotica undecimpuncta howardi Barber|
|Description and Biology: The larva of this pest is the southern corn rootworm; the adult is the spotted cucumber beetle. The larva, slender with a brown head and white or pale yellow wrinkled body, grows to about 15 mm long. The last segment of the abdomen has an almost circular margin and is brown. The 6-mm-long adult beetle is yellowish-green with eleven black spots on its forewings. It has a black head and antennae one-half to two-thirds the length of the body. The adult overwinters in shelters of trash or is active during mild winters. In spring, females deposit eggs in the soil around the base of plants. There are two generations a year.|
|Symptoms and Damage: The southern corn rootworm feeds on and bores into roots of sorghum or enters the stalk just above the roots. It feeds in the crown area of young plants, destroying the apical meristem and preventing growth of the main stem. Symptoms of damage are stunting and “dead hearts.” Young plants are affected most often. Delayed and nonuniform maturity may result from production of tillers. Weed abundance increases because of stunted sorghum plants. Plant lodging may occur later in the season.|
Monitoring: Southern corn rootworm cannot be controlled after the crop is planted, and abundance cannot be determined before planting. A history of southern corn rootworms in a field of sorghum is the only way to assess the need to apply insecticide for control. This fact increases the importance of appropriate cultural practices.
Management: Cultural control practices include keeping fields free of grassy weeds, plowing and disking thirty days before planting, rotating with a nongrass crop, planting early, and planting at a slightly higher than normal seed rate. In-furrow, at-planting application of granular or liquid insecticide also is effective.