Grain Sorghum Midge Management
August 14, 2023
Identification
Sorghum midge (Stenodiplosis sorghicola) is a widely distributed pest in grain sorghum. It is a small (1/16th inch or less), reddish orange fly that pupates from a colorless larva. The legs and antennae are dark brown or black, but magnification is needed to help detect these subtle hue differences as the insect matures. This pest has also been described as resembling an orange mosquito with its pointed ovipositor.
Damage and Symptoms
Sorghum midge is often present and associated with flowering grain sorghum. It can also be found on Johnsongrass as it is another important host. The females lay eggs directly into the ovary of fertilized sorghum seed where the larvae hatch and feed which prevents kernel development. Glumes of affected spikelets are compressed together due to the lack of kernel development. In heavily infested sorghum heads, there can be a mix of kernels and blank, undeveloped areas because of midge feeding.
Scouting
Look first at the edges of the field downwind from pollinating heads. If they are abundant and at or near the threshold, then proceed to scout further out into the field until a representative sample is achieved. The economic threshold is 0.5 sorghum midge per head.1 The use of a clear plastic bag or white bucket can be helpful to identify this pest due to its small size. Place a bag over the pollinating sorghum head and hold or secure the base of the bag around the stalk under the grain portion of the head while attempting to keep it somewhat inflated. Shake the head gently or make a loud noise such as clapping, and the insects should attempt to flee or fall off the head into the bag. Clapping or another loud sound over the top of a pollinating head can also cause the flies to scatter when trying to detect them in a field. They are weak fliers so a white bucket (for visual contrast) can also be used to collect them. Depending on flowering uniformity, one to three weeks of scouting may be necessary to manage this pest when grain sorghum is most vulnerable.
Management
Using a solid IPM or integrated pest management system is the best approach to preventing economic losses with sorghum midge. In known high pressure areas, a sorghum midge resistant seed product should be considered. Planting early into optimal conditions including uniform seed placement to encourage uniform emergence, pollination, and maturity is arguably the most effective cultural management strategy. For irrigated acres, timely waterings can help maintain uniformity to help prevent delayed heading that is attractive to these pests. Manage areas of Johnsongrass to prevent alternate host cites for sorghum midges. Deep tillage to bury sorghum midge infested residue is effective to reduce the numbers of overwintering larvae. Chemical management options are available and depending on the sorghum midge populations, multiple applications may be needed if a suitable product cannot provide enough residual activity to maintain control. In these cases, scouting every two to three days may be necessary while maintaining the proper re-entry intervals depending on the situation and product applied.
Brooks Brenn
CHANNEL Agronomist
Sources:
1Biles, S. 2021. Midge in grain sorghum. Mid-Coast IPM. Texas A&M AgriLife Extension. Texas A&M University. https://agrilife.org/mid-coast-ipm/2021/06/02/midge-in-grain-sorghum/
Insect pests of sorghum. Texas A&M AgriLife Extension. Texas A&M University. https://agrilife.org/sorghumipm/insect-pests/sorghum-midge/#:~:text=Sorghum%20Midge%201%20Description%20and%20Biology%20The%20sorghum,adults%20must%20be%20assessed.%20...%204%20Management%20
Sorghum midge. OSU Extension. Oklahoma State University. https://extension.okstate.edu/programs/digital-diagnostics/insects-and-arthropods/sorghum-midge-contarinia-sorghicola/
The sorghum midge. South Texas Field Crop Entomology. Texas A&M AgriLife Extension. Texas A&M University. https://agrilife.org/sca/the-sorghum-midge/
Web sites verified 7/17/23. 1110_282551
