Grain sorghum is in all stages across the state from whorl stage to head fill. Each stage may be experiencing it’s own unique set of insect problems. We have some very late plantings that are in the whorl stage experiencing some significant pressure from fall armyworms. In some instances nearly 100% of the plants are infested and showing heavy damage and should be treated.
Sorghum that is in the flowering stage (see picture above) should be scouted for sorghum midge. Sorghum midge is the most damaging insect pest of grain sorghum, but only attacks sorghum during flowering. The small orange colored adults lay eggs in flowering sorghum. Because they are quite small, it is easiest to scout for these insects in the morning hours before winds pick up. Fields should be treated when an average of 1 or more midge adults per head are found. The field should be rechecked in 4 or 5 days if still flowering. Midge are easy to control with a properly timed insecticide application. Late plantings are more prone to having heavy midge infestations.
We are also seeing a few corn earworms showing up in sorghum heads as well. Often there may be a complex of corn earworm, fall armyworm and sorghum webworm feeding on heads. Treatment level for corn earworm and/or fall armyworm is when an average of 1 caterpillar 1/2-inch long or longer is found per head. Sorghum webworm treatment threshold is somewhat higher at 5-6 caterpillars per head. Shy away from using pyrethroids if possible and use Belt, Prevathon, Besiege or Lannate for headworms. For a list of recommended insecticides consult the grain sorghum section of MP144 Insecticide Recommendations for Arkansas.
Sugarcane aphid has been detected on sorghum in Southeast Arkansas and has moved up to Phillips county at this time. We expect it will continue to move north as the season progresses. Dr. Nick Seiter has an earlier post (Pest Alert: Sugarcane Aphid in Sorghum) with some good information on this pest. Arkansas has also been granted a Section 18 for use of Transform for sugarcane aphid (see below).