Soil sample tests in North Dakota indicate a dramatic increase in levels of overwintering wheat midge larvae, says Janet Knodel, North Dakota State University Extension Service entomologist.
"We haven't seen such high populations of wheat midge since the mid-90s," she says.
This winter, wheat midge larval cocoons ranged from zero to 3,750 larval cocoons per square meter and averaged 417 larval cocoons per square meter.
Last winter, the average was just 129 with a range from zero to 750.
"This is an alarming increase in the wheat midge population with pockets of 'high risk' in certain counties," Knodel says.
Populations of cocoons exceed 1,200 per square meter in seven counties -- the eastern half of Divide, most of Burke, northern Renville, southeastern Mountrail, western and eastern edges of Ward, western McHenry, and west-central McLean.
If wheat is planted in these areas, be prepared to monitor their fields closely for wheat midge infestations, and include the cost of an insecticide treatment wheat production budgets, Knodel says. Otherwise, undetected and uncontrolled infestations may result in significant yield losses and/or unplanned pesticide costs.
"Wheat midge populations of greater than 500 to 1,200 larval cocoons per square meter have expanded into eight counties from five counties last year," Knodel says. "Pockets were found in south-central Bottineau, central Ward, central Cavalier, west-central Towner and north-central Walsh, in addition to the previously mentioned counties with a high risk.
Areas where populations are above 500 larval cocoons per square meter also require close monitoring. If the wheat crop is heading during adult wheat midge emergence, wheat midge can cause severe injury to the kernels and yield loss can occur.
There also are several pockets of 201 to 500 larvae per square meter in most of the remaining counties, except in Eddy and Nelson. Areas with more than 200 larval cocoons per square meter should be scouted to determine if an action threshold population level exists. However, these areas are considered lower risk.
Weather conditions prior to and during adult wheat midge emergence will affect population levels. Conditions that favor midge development and outbreaks include high soil moisture in late June and warm, calm and humid conditions during the egg-laying stage in early to mid-July.
Source: NDSU Extension Communications