|Cutworms: Numerous species, Family Noctuidae|
|Description and Biology: Cutworms are the larval stage of nocturnal moths, several species of which damage sorghum. The typical cutworm larva attacking sorghum has a plump, curled-up appearance. Larvae are smooth, but vary in color from grayish-white to grayish-black or brown depending on species. Fully-grown larvae are 30 to 50 mm long. Most cutworms overwinter as partly- to fully-grown larvae. Some species, however, hibernate as adults, and others hibernate as pupae in the soil. Cutworms usually remain during the winter as small larvae in cells in the soil, under trash, or in clumps of grass. They start feeding in the spring and continue growing until early summer, then pupate in the soil. Depending on species, generations per year varied from one to four or five. Larvae of most species remain underground during the day and emerge to feed at night. Eggs are laid on stems or leaves of grasses, such as sorghum, or weeds or on soil and hatch in two to 14 days. Some moth species prefer to lay their eggs in low areas of fields or those subject to overflow. Often these areas have an abundance of weeds.|
|Symptoms and Damage: Cutworms of different species may damage sorghum plants in three ways: 1. some cut off sorghum plants at or slightly below the surface of the soil (surface-feeding cutworms), 2. some feed on above-ground plant parts (climbing or army cutworms), 3. others (subterranean cutworms) feed on underground plant parts including roots of seedlings. Plants with severed stems die. Leaf feeding by cutworms causes ragged leaves, while root-feeding cutworms cause small plants to die and larger plants to be stunted.|
Monitoring: Determining the presence of cutworms in sorghum is based on visible damage to plants. For surface-feeding cutworms, the number of severed plants per meter of row should be determined. A decision to apply insecticide should be based on the degree to which an adequate stand is threatened. For cutworms that feed on above ground plant parts, significant loss occurs when more than about 30% of leaf tissue has been eaten. Cutworms that feed below ground should be sampled for prior to planting sorghum, especially in areas with a history of subterranean species.
Management: Cultural controls include plowing under vegetation in late summer or early fall, thoroughly preparing the seedbed at least three to six weeks before planting, and maintaining good weed control. Cutworms are more severe in weedy fields. Herbicides may be used to kill winter weeds, thus reducing the potential for cutworm damage. Insecticide spray used as a broadcast treatment usually protects plants from cutworms. However, cutworms hide in the soil during the day. Late-afternoon applications sometimes are more effective. Poisoned baits are available and effective against some species, but are expensive. Subterranean cutworms can be suppressed with insecticide applied to soil at planting. Insecticide applied at planting should be incorporated into the top 2.5 to 5 cm of soil in a 15- to 18-cm band. Aerial or ground application of approved insecticides is effective in controlling cutworms feeding above ground on sorghum plants. However, such insecticide applications are more effective on climbing than subterranean cutworms. Also, such insecticide is more effective when the soil is moist rather than dry.