By Jeff Whitworth
It is important to monitor flowering/heading sorghum fields for corn earworm, also known as sorghum headworm. Flowering sorghum heads sampled so far this year indicate that headworm populations are just getting started throughout north central Kansas.
There are multiple generations of this pest each summer and later generations will 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)
Infestations are common throughout Kansas, and sorghum is vulnerable to infestation from bloom through milk stages. Larvae are active from August to October. Generally, expect a loss of 5% yield per larva, per head. So, one larva per head will result in 5 percent yield loss, two in larvae per head, 10% loss, and so on.
Producers should begin scouting fields now to detect headworms while they are still small. 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.