The dry conditions this growing season have extended into early fall, and that may prove helpful in reducing the threat of wheat midge in 2013 — and lower the costs to control them through insecticides.
Janet Knodel, entomologist and associate professor at North Dakota State University, said a higher mortality rate of wheat midge larvae is likely due to the lack of moisture and hard, compacted soil conditions right now.
The midge larvae attempt to burrow into the ground to form cocoons over the winter, but that’s going to be a challenge given the hard soil.
The larvae may fall into cracks and holes in the ground but won’t get very far down. And as a result, the larvae is susceptible to natural enemies, such as ground beetles, Knodel said. They also fall victim to dessication.
Wheat producers have had to contend with the midge for nearly 20 years. Its believed to come down from Canada. and began showing up in fields in North Dakota as early as 1993, Knodel said.
North Dakota County Extension Agents are in the process of completing fall soil surveys and those samples will help to determine cocoon numbers and what impact they could have on next year’s wheat crop in various regions across the state.
A brine flotation method is used to analyze the soil samples for wheat midge cocoons. Knodel said it’s a labor-intensive process that takes a few months to complete. By next February, wheat producers should have a clearer picture of the midge threat once the overwintering midge survey is released.
Of the 142 soil samples from 20 counties collected last fall, and analyzed earlier this year, only 12 percent were rated moderate to high risk, Knodel said.
Although wheat midge populations are on the decline, there were still a few pockets of the state where the risk was moderate to high. That included the northwestern and north-central regions of the state.
The decrease in the wheat midge population can be attributed to the wet spring of 2011, which pushed back small grains planting into early June. This was later than the typically early to mid-May planting date. And based on the planting model for susceptibility to wheat midge, was just within the 600 growing degree days, which is the end of the susceptible period of wheat to wheat midge. Late planting dates, after 600 growing degree days, can mitigate midge damage.
In addition, a large amount of agricultural acreage went into prevent planting, especially in the northwestern region of North Dakota, according to the 2012 midge report. This reduced the availability of host crops to wheat midge.
The midge attacks between the heading and flowering stage of the crop. This Insecticides are warranted when a midge is detected for every four or five heads.