With our major corn earworm flight underway, there are numerous reports of small corn earworm larvae in sorghum heads. Because we generally don’t worry about worms as an economic problem in vegetative-stage sorghum, I recommend sampling once you have a head. To sample sorghum, you should visit the field in several places, with six being a good rule of thumb. At each location, randomly sample about ten plants by shaking the heads into a bucket. Generally when corn earworm is disturbed, it will curl up and lie still, so look for movement in the bottom of the bucket. Once you are done sampling, average your number of finds together. If you average at least one corn earworm per head, it may be worth considering an insecticide treatment.
Treatment will generally be more effective in sorghum varieties that have a looser head, since the insecticide will penetrate more easily. I recommend a pyrethroid for corn earworm and Lannate for fall armyworm. Fall armyworm should be sampled in the same way as corn earworm. Treatment should be based on the same threshold.