Authors: Dr. Phillip Roberts, Dr. Paul Guillebeau, University of Georgia
Larvae have four pairs of abdominal prolegs and thrash vigorously when disturbed. Larvae vary in color from green to brown or black and reach a maximum length of 48 mm. Larvae have a light, dorsal stripe bordered by broad, dark stripes and a broad white, longitudinal stripe on each side. The adult or moth has a wingspan of 30 to 38 mm. The forewings are ash gray, light yellowish-brown, or dark-reddish brown. The hind wings are cinnamon brown with a row of light spots near the margin. When the wings are fully extended, a dark diagonal line extending across both sets of wings is evident.
Soybean is the primary host. Thirty-three other legume species including peanut are recognized hosts. Only five other host plants from three plant families are known.
Newly emerged caterpillars feed on the lower leaf surface of upper leaves. Later instars consume the entire leaves. After the upper leaves have been consumed, foliage in the middle and lower parts of the canopy are consumed. Complete defoliation may occur.
Velvetbean caterpillars survive the winter in tropical areas and migrate into Georgia in late spring and early summer. Eggs are laid singly on the underside of leaves and hatch in about three days. Larvae feed for 15 to 30 days and pupate in the soil. During summer months a generation is completed in about 4 weeks. Three to four generation occur in Georgia each year.
Velvetbean caterpillar is an annual pest on Georgia soybeans. Control is good with insecticides. However, severe defoliation can occur if infestations go undetected. A preventive treatment with diflubenzuron has shown promising results.
Soybean treatment thresholds:
- Prior to full bloom: defoliation reaches 30 percent.
- Full bloom until mid pod-fill: defoliation reaches 15 percent.
- After full pod-fill: defoliation reaches 25 percent.