We have a good bit of grain sorghum in the county and some is starting to head and the rest has already flowered and moving to dough stage in the grain. This sorghum was planted after watermelons and looking great. These are 15 inch rows with two different plantings because of rain. It’s starting to head out now, but is very early heading. Only a few spots uniform. Sugarcane aphids were a bid deal in grain sorghum when was working further southwest. We have not seen any aphids so far with none in the field yesterday. This is good news and will actually help our management of sorghum midge. We are having some caterpillar damage now on younger sorghum.
Sorghum midge is probably the most common insect pest at heading. It’s a small, orange or reddish fly. Keep in mind, grain sorghum flowers from top to bottom. Midge can be more difficult to scout for. Once grain heads come out, we need to be looking for midge. It starts flowering right when the head comes out. You know it’s flowering when you see the yellow anthers. This is the only part susceptible to midge. Once they turn orange, it is no longer susceptible. Basically, the glume opens to put our yellow anther to pollinate, and the midge lays an egg inside there.
Once flowering is complete, midge is not an issue. One way to scout is take a paper plate, and slap the head in the plate. Dr. Angus Catchot, entomologist in Mississippi, shows on Scouting For Sorghum Midge With Confidence, a method of putting a gollon ziplock bag over the grain head and thumping it. The midges fly to the top of the bad, and you don’t have to close the bag.
The threshold for treating midge is 1 adult/head after 25-30% of heads are blooming. Treat again 5 – 10 days later if many heads are still blooming and 1 midge/head is found. There are many insecticide options. The main thing is if sugarcane aphids are present, do not use pyrethroids due to flaring aphids. This is why we don’t do automatic midge sprays.
We are also seeing caterpillars on the younger sorghum. Most of the caterpillars we are seeing are fall armyworms. We don’t have enough to treat right now. Since we are starting to head, we need to scout for worms there.
Whorl stage threshold: We don’t treat unless 40% or more plants in the field are infested with caterpillars. UGA Extension Entomolgoist Dr. David Buntin says economic losses probably do not occur unless population levels exceed 1 larvae per plant.
Grain head threshold: Our threshold is to treat when an average of 1 or more (1/2 inch or larger) corn earworm or fall armyworm are found per grain head. For sorghum webworm, treat when 5 or more small (1/4″) larvae per head are found.
The rest of our grain sorghum is much further along and past the stage of midge injury. Here are a few pictures from Hatley the other day: