One of the most damaging insect pests of grain sorghum continues to be sorghum midge and this year’s early wet soil conditions that delayed sorghum planting in some cases, will promote conditions for midge to be a problem as grain sorghum will be flowering over several weeks.
In a brief summary here is what the sorghum midge does to sorghum. The adult sorghum midge is a tiny, fragile looking, orange fly. Larvae hatch from eggs deposited by a female midge in spikelets of flowering sorghum heads. Each female deposits about 50 tiny, yellowish white eggs during her short lifetime of less than 24 hours. An orange maggot hatches from the egg and feeds on the newly fertilized ovary, thereby preventing kernel development.
Because midges lay eggs in flowering sorghum heads (yellow anthers exposed on individual spikelets), damage can occur until the entire head or field of sorghum has flowered. The period of midge susceptibility may last from 7 to 9 days (individual head) to several weeks (individual field) depending on the uniformity of flowering. The good news this year is that most of our sorghum fields are uniform in their flowering, due to good soil moisture at planting.
Fields should be inspected mid-morning to shortly after noon when midge are most abundant on flowering heads. The simplest and most efficient technique for detecting and counting sorghum midges is careful, close-range inspection of all sides of a randomly selected flowering head. Since they are relatively weak fliers and rely on wind currents to aid their dispersal, adult sorghum midges are usually most abundant along field borders.
The need to apply insecticidal control is based on the number of adult midges during the flowering period, and based on today’s grain prices and potential yield, an average midge density of 1 midge per panicle (head) or greater would probably warrant insecticide treatment. Insecticide residues should suppress sorghum midge egg laying for 1 to 2 days after treatment. If adults are still present 3 to 5 days later, immediately apply a second treatment. If midges are present the day following treatment, it does not mean you do not have protection for the heads; midges could be re-infesting the field, which is common.
More information about managing sorghum insects can be found at the AgriLife Bookstore found on the Internet website: http://agrilifebookstore.org/ by entering publication number B-1220.