Although the sorghum midge (an orange fly about the size of a gnat) is very tiny, it can be very destructive to grain sorghum. It is considered the most destructive pest of grain sorghum in Arkansas. Sorghum midge has the potential to drastically reduce yields if it is not managed properly.
We’ve seen an increase in the number of fields requiring treatment and an increase in damage from this pest over the last couple of years.
The sorghum midge has a very short lifespan as an adult, the stage in which they must be controlled. Adults only live about 24 to 48 hours, during which they mate and lay eggs. This gives them a short window in which to attack grain sorghum.
They lay eggs only in flowering grain sorghum, leaving a very short window in which growers can begin control measures.
Early in the season, midge will reproduce on johnsongrass. Fields in the vicinity of johnsongrass should be scouted closely for this pest when flowering begins (adults will lay eggs on flowering heads).
The egg hatches into a legless larva or maggot and begins to feed on developing seed. Because the larvae are inside the seed, they are difficult, if not impossible, to control with foliar insecticides. The adults, on the other hand, are easily controlled with foliar insecticides. Therefore, target applications towards adults to manage this insect pest.
Because midge lay eggs only in flowering sorghum, flowering is the time at which fields should be scouted. I’ve been called to a field many times about midge after flowering had passed. We can find many blank seed spikelets with white pupal cases hanging where adults have emerged.
By that time it is too late to do anything about the midge. They already have done their damage and the next generation has moved on to another field that is, of course, flowering.
Keep in mind that it can be difficult to find the tiny adult flies. They are not strong fliers and nearly impossible to find on windy days. Try to scout for them in the morning, before the wind gets up too high.
Treat when an average of one midge adult per head is found in flowering sorghum. The field should be checked again in four or five days if it is still flowering and it should be treated again if midges are above the threshold of one per head.
Several Arkansas fields have required more than one application in the last few years. Consult your local Extension agent for current recommendations on insecticides for controlling this pest.
Although the sorghum midge can be devastating to sorghum, it can be easily managed if fields are scouted and insecticides are applied in a timely fashion. Any field that is flowering should be scouted as soon as possible. Don’t wait too long to scout fields for this pest or it may be too late to do anything about it.
Glenn Studebaker is an Extension entomologist with the Cooperative Extension Service, University of Arkansas.