Wheat midge populations should be lower this year. Soil samples in North Dakota indicate lower levels of overwintering wheat midge larvae for the 2012 season.
Only 12% of the samples statewide show moderate to high risk for wheat midge infestation.
"Most wheat producers should get a break from insecticide costs," says Janet Knodel, North Dakota State University Extension entomologist.
The pockets of moderate to high risk are in northwest and north central North Dakota.
The high risk areas are in central Burke and southwestern McHenry counties.
"If wheat is planted in these high-risk areas, be prepared to monitor the fields closely for wheat midge infestations and include the cost of an insecticide in wheat production budgets," Knodel says. "Undetected and uncontrolled infestations may result in significant yield losses."
Areas at moderate risk are in central Divide, central and southeastern Bottineau, eastern Ward, west-central McLean, southwestern McHenry, northern and southern Pierce, western Rolette and southern Cavalier counties.
Close monitoring for wheat midge will be required in these areas to protect yield potential, Knodel says.
Knodel attributes the decrease in overwintering midge larvae to last year's delayed planting of wheat and the decrease in wheat acres due wet weather. There wasn't as much wheat planted and in the right stage of development to support an increase in wheat midge populations.
This year, early planting and selecting an early maturing variety spring wheat variety will be two of the best ways to protect wheat from midge.
"Early planting (prior to 200 growing degree days using a base of 40 F) can reduce midge damage because the wheat will flower before peak midge emergence," Knodel says. "Wheat is most susceptible from heading to 80% of the primary heads with anthers. Planting between 200 and 600 degree days is the high-risk window for planting wheat because wheat midge will be emerging during heading."
If you must plant during this window, stagger planting dates, she recommends. Late-planted wheat (after 600 degree days) will miss the peak emergence of wheat midge but runs the risk of lower yields, frost damage or even greater losses due to barley yellow dwarf virus, which is a virus transmitted by cereal aphids.
The parasitic wasp, Macroglenes penetrans, plays an important role in keeping wheat midge in check naturally most years by killing the wheat midge larvae. The average parasitism rate for the wasp was 19% in 2011, compared with 17% in 2010 and 13% in 2009.
Parasitism ranged from 0-100% across the state, with the higher rates occurring in areas where midge populations have been high the past few years. More than half of the samples in 2011 (52 percent) had zero parasitism, which could cause wheat midge populations to increase in future years.
"We need to continue to conserve parasitic wasp populations when possible by spraying insecticides only when necessary," Knodel says. "Also, avoid any late insecticide applications to minimize any negative impacts on the parasitic wasps, which are active at that time."
The soil samples for the survey were collected by NDSU Extension Service agents in the fall of 2011. Midge larvae are extracted from the soil samples in Department of Entomology laboratories at NDSU. The North Wheat Commission helped fund the soil survey.Source: NDSU Extension Communications