Velvetbean Caterpillar in Soybean

Crop Damage

Velvetbean caterpillar (Anticarsia gemmatalis) is a major defoliating pest of soybean in the southern United States, particularly from South Carolina westward to Arkansas. Although this migratory insect is occasionally found in Midwestern soybean production regions, it is generally considered a sporadic pest.

Young larvae feed primarily in the upper soybean canopy, removing the epidermis and mesophyll from the lower leaf surface. As larvae mature, they consume entire leaflets, move throughout the plant canopy, and continue feeding on older foliage. In addition to leaves, larvae may feed on stems, buds, and pods.

During outbreak years, large populations can rapidly defoliate soybean fields, resulting in substantial yield loss.

Pest Description

Young larvae are typically green but may become olive green, brown, or nearly black as they mature. Fully grown larvae reach approximately 1 3/4 inches long and have alternating light and dark longitudinal stripes that extend from behind the head along the sides of the body.

A distinguishing characteristic of velvetbean caterpillar larvae is the presence of four pairs of abdominal prolegs. Velvetbean caterpillars may be confused with corn earworm larvae; however, when disturbed, velvetbean caterpillars thrash vigorously, whereas corn earworms typically curl into a C-shape.

Adult moths vary in color from gray to brown. A key identifying feature is a dark line that extends diagonally across the forewing and continues onto the hindwing when the wings are folded at rest.

Scouting and Management

Scouting procedures and treatment thresholds for velvetbean caterpillar vary among states because the insect is an occasional pest in many soybean-producing regions. Consult local Extension recommendations for region-specific guidance. Several sampling methods can be used to assess velvetbean caterpillar populations. When using a sweep net, take 25 sweeps in at least four representative locations throughout the field. Ensure the sweep net samples deep into the canopy, as larvae often move lower in the plant as they mature. Count the number of larvae collected at each location and calculate the average number per 25 sweeps. Treatment thresholds generally range from 25 to 38 larvae per 25 sweeps. When using a drop cloth, place a 3-foot-long drop cloth between rows and vigorously shake plants so larvae fall onto the cloth at 10 or more locations. Count the number of larvae and calculate the average number per row foot. Treatment thresholds generally range from 4 to 8 larvae per row foot. For defoliation estimates, randomly select plants throughout the field and estimate defoliation across the entire canopy. Use the Crop Protection Network’s Insect Defoliation Tool to improve the accuracy of defoliation estimates. Standard soybean treatment thresholds are 30% defoliation during vegetative growth stages and 20% defoliation during reproductive growth stages. 

When making management decisions, consider the impact of other defoliating insects that may be present. Also assess whether larvae have been parasitized or infected by fungal pathogens, as natural enemies can substantially reduce populations. Soybean varieties with partial resistance to velvetbean caterpillars are available but do not provide complete protection. Adjusting planting dates may help reduce the risk of late-season infestations.

Developed and reviewed by Carol Pilcher, Iowa State University and Robert Wright, University of Nebraska-Lincoln, with support from the United Soybean Board.