Wheat growers urged to check for orange blossom wheat midge larvae

Early field scouting at the Montana State University Experiment Station in Creston indicates high levels of orange wheat blossom midge larvae earlier than expected this season. Spring wheat growers are being urged to survey their fields to determine if they will have a problem.

Larvae may be found on the soil surface or within two to four inches deep in small round cocoons. Adults emerge over a 4-6 week period around the time of wheat head emergence and flowering. The wheat midge is a small, delicate, mosquito-like fly that is orange in color. Females fly beginning at dusk when temperatures are above 59 degrees Fahrenheit and wind speed is below six mph.

Eggs are deposited on florets on developing kernels just before flowering. Eggs hatch in 4-7 days and orange-colored larvae feed on developing kernels. The larvae feed on the developing kernel, reducing grain size by 30 to 50 percent per larvae, negatively affecting yield, grade and quality.

There are several methods available for detecting the presence of the midge. However, scouting is the only recognized way of arriving at an accurate decision to treat a field. Scouting should be done after 8:30 p.m. to coincide with when the females are most active and fields should be inspected in at least three to four different locations.

Treatment threshold values vary; however, in many wheat growing areas, insecticide treatments are recommended if one or more adults are observed for every 4-5 heads. When wheat prices are high, treatments may be justified if there is one adult per seven to eight wheat heads. Provided that threshold values are present, the optimum stage to apply an insecticide is when 70 percent of the spring wheat crop is headed.

The midge is difficult to scout for. Densities might be high, but scouting efforts may fail to reveal their true numbers if evening temperatures are cool, humidity is low, or wind speeds are high. And, because adults emerge over several weeks, late developing tillers or areas in the field where heading is delayed such as low spots where soil moisture is favorable, will continue to be vulnerable to attack.

Insecticides: Although chemical control measures are available, their efficacy is highly dependent on precise timing of spray applications. Wheat is most susceptible to midge damage when egg laying occurs from early heading through pollination. As such, fields should be monitored daily from the time the heads begin to emerge from the boot until the anthers are visible.