Populations of the sorghum midge, Contarinia sorghicola (Coquillett), are maintained at low levels in johnsongrass, Sorghum halepense (L.) Pers., from late spring to mid-summer. A slow buildup occurs on grain sorghum, S. bicolor (L.) Moench, during early August, and numbers capable of causing severe yield reductions are reached after ca. 20 August. Fields planted prior to 15 June will likely escape midge damage. Those planted between 15 and 22 June may or may not escape damage, depending on the season. Virtually all plantings made after 22 June risk severe midge infestations and yield reductions.

Plant population appears to have little influence on ultimate yield. The yields in plots thinned to 13 and 26 plants per meter were not significantly different from those thinned to 39 plants per meter, although the midge infestation in heads from the low plant population was more than double that in heads from the high plant population. Plants in the low population produced larger heads and were able to tolerate a much higher level of infestation without suffering a yield reduction.