North Dakota expects fewer wheat midge in 2012 and the outlook is similar for Manitoba.
There could be some localized hot spots in western Manitoba but overall populations of the insect that can damage wheat kernels will be low to moderate, says Manitoba Agriculture, Food and Rural Initiatives entomologist John Gavloski.
The presence of wheat midge doesn’t necessarily result in damaged wheat, Gavloski said. Once wheat produces anthers midge is no longer a threat.
“If the wheat is producing anthers by early July your wheat is already naturally resistant to midge regardless of what variety you’re growing,” he said. “The vulnerable stage for wheat is from as soon as that head is visible until the anthers are produced, but once the anthers are produced chemical changes are occurring in the wheat kernels making them essentially resistant to the midge.”
The vulnerable stage can be just a matter of days, depending on temperatures; the warmer it is the faster flowering begins and ends.
There will be fewer midge if the spring is dry, he said. Midge pupa require soil moisture before going into the adult stage.
A parasitic wasp called Macroglenes penetrans plays an important role in keeping wheat midge in check naturally most years by killing the wheat midge larvae, Gavloski said. That’s why it’s critical that farmers only spray wheat midge when populations warrant and wheat is in the susceptible stage.
Don’t spray its enemies
“We really do discourage people from spraying wheat midge just in case because you can do more harm than good by taking out the parasites,” he said. “If they are naturally keeping your wheat midge population in check below economic levels and you end up spraying you’re probably spraying out more parasites than you are midge and that could result in further problems down the road. Only spray when needed — that’s the main message.”
Farmers should search for wheat midge in susceptible fields at dusk. The adult midge fly is much smaller than a mosquito, but is distinct because of its orange colour. Winds must be calm or the midge might not fly.
Researchers haven’t determined how many midge it takes in an area to cause economic damage to a wheat crop, Gavloski said. Trying to count tiny midge flies on wheat heads at dusk is almost impossible. Gavloski suggests coating a pie plate with vegetable oil so the insects will stick and doing some sweeps through the heads.
“If you’re having trouble finding the midge you probably don’t have an issue,” he said. “Fields that have economical population you will see them flying around.
“If you do just a few sweeps and your plate is just covered in orange you probably have a problem (if the wheat hasn’t produced anthers yet).”
Last year’s wet weather and delayed wheat planting cut wheat midge populations in North Dakota, North Dakota State University Extension Service entomologist Janet Knodel said in a recent news release.
Soil samples were taken in North Dakota to assess the midge risk. Based on the number of overwintering wheat midge larvae (cocoons) only 12 per cent of the samples point to a moderate to high risk.
“Although the wheat midge populations fell from last year’s high, there still are a few pockets of moderate to high risk that need to be monitored closely in the northwestern and north-central regions of North Dakota,” Knodel said.