It is important to monitor flowering/heading sorghum fields for corn earworm, also known as sorghum headworm. Flowering sorghum heads sampled on August 21 indicated approximately 25% of the heads were infested with various sizes of larvae.
Although larvae of this moth prefer corn, they sometimes infest sorghum heads. The head capsule is light brown, and the body color varies from pink to green to brown with light and dark stripes along the length of the body. Larvae can be 1.5 inches long at maturity.
Figure 1. Sorghum headworm (corn earworm). Photo by K-State Research and Extension.
Infestations are more common in southern Kansas, and sorghum is vulnerable to infestation from bloom through milk stages. Larvae are active from August to October. One to two larvae per head can result in approximately 5 to 10 percent yield loss.
Producers should begin scouting fields now and consider treatment where infestations average five or more worms per head during the early post-bloom period. The decision to treat should balance the expected yield and crop value against treatment cost and the amount of damage that can be prevented. The average size of larvae at detection is a key consideration, because less will be gained by treating older, larger larvae.
Please refer to the most recent version of the Sorghum Insect Management Guide for specific control recommendations.
Jeff Whitworth, Extension Entomology
Holly Davis-Schwarting, Research Associate