Schmidt: Wheat midge survey results and forecast
Wheat midge populations are expected to be lower in 2015 than 2014, except for a few hot spots in Williams, Divide and Mountrail Counties.
Soil samples in North Dakota indicate decreasing levels of overwintering wheat midge larvae (cocoons) for the 2015 season, according to Janet Knodel, North Dakota State University Extension Service entomologist.
A total of 196 soil samples were collected from 21 counties to estimate the regional risk for wheat midge. The distribution of wheat midge in the 2015 forecast map is based on unparasitized cocoons found in the soil samples collected in the fall of 2014.
A degree day model is a good predictor of wheat midge emergence for timing field scouting and is based on spring wheat development. It is available on the NDSU North Dakota Agricultural Weather Network website at ndawn.ndsu.nodak.edu/wheat-growing-degree-days.html.
“It’s looking like an early spring in 2015, and early planting (prior to 200 degree days for wheat midge) is a good way to decrease wheat midge damage since the crop will be in susceptible growth stages before the wheat midge emerges,” says Knodel.
The economic thresholds are the same as past years: 1 or more midge are observed for every 4 or 5 heads on hard red spring wheat, or 1 or more midge are observed for every 7 or 8 wheat heads on durum wheat. If wheat scab is a problem due to wet conditions during flowering, most insecticides labeled for wheat midge control can be tank-mixed with a fungicide.
Beside the good news of wheat midge populations being low, the parasitic wasp, Macroglenes penetrans, which kills wheat midge larvae has increased slightly to 11 percent parasitism from 7.6 percent in 2013. “Although the parasitic wasp -wheat midge populations are cyclic, wasps play an important role in keeping wheat midge controlled naturally,” says Knodel.
Parasitism rates ranged from zero to 100 percent across the state, with the higher rates occurring in areas where midge populations have been high over the past few years, such as Burke, Divide and Williams Counties. Seventy-three percent of the larval cocoons had zero parasitism in 2014.
“We need to continue to conserve parasitic wasp populations when possible by spraying insecticides only when wheat midge populations are at economic threshold levels, and avoiding any late insecticide applications to minimize the negative impacts on the parasitic wasps that are active at that time,” Knodel says.
The soil samples were collected by NDSU Extension Service agents in the fall of 2014.
The wheat midge survey is supported by the North Dakota Wheat Commission.