I have received a few phone calls regarding sorghum midge in Northeast Louisiana. Sorghum midge is small insect (1/8 inch or smaller) that has dark wings and an orange body. The sorghum midge is primarily found on grain sorghum and Johnson grass with both hosts playing an important role in overwintering and reproduction. Adult midges will emerge in the spring and often complete two generations on Johnson grass before moving into grain sorghum.
Sorghum midge females may lay as many as 50 eggs in the flowering spikelets of sorghum with resulting damage occuring during bloom. The developing larvae feed on fertilized grain ovaries preventing kernel development. Affected sorghum heads will have blanked or irregular grain patterns. Early planted sorghum will often have lower populations of sorghum midge than later plantings. Promoting crop uniformity will also help reduce the instance and severity of sorghum midge. Johnson grass should be destroyed in and around field borders with all crop residue destroyed after sorghum harvest.
Scouting for sorghum midge can be difficult, especially in windy conditions. Additionally, sorghum midge only attack flowering sorghum, which occurs during the morning. Scouting sorghum for midge after 1 pm is almost always ineffective. Also, sorghum midge adults live only 1 day so each day is a new brood of midge. Thus, flowering sorghum should be scouted daily if possible, twice weekly at minimum. Because midge are weak flyers, infestations will typically begin along field borders and spread downwind from alternative hosts (Johnson grass).
The simplest and most efficient way to scout for sorghum midges is to carefully inspect all sides of randomly selected flowering grain heads. Handle grain heads carefully during inspection to avoid disturbing adult sorghum midges, and counting the adults present. Other sampling methods can be used, such as placing a clear plastic bag or jar over the sorghum grain head to trap adults. Scouting should begin once the plants are averaging 25-30% bloom.
The threshold for sorghum midge in Louisiana is 1 or more midge per head. Because new unprotected blooms emerge every day, additional insecticide applications at 5-7 day intervals may be needed. There are a number of pyrethoids that are effective towards sorghum midge as well as Lorsban/chlorpyrifos and Lannate.
If you have any questions or concerns please contact Sebe Brown or Dr. David Kerns for more information.
Sebe Brown Cell: 318-498-1283 Office: 318-435-2903
Dr. David Kerns Cell: 318-439-4844 Office: 318-435-2157