Timing is everything and that goes for wheat midge too. Starting now, prairie producers need to be on the lookout for the insect pest.
Combine this year’s high moisture with a series of normal heat unit days, and midge numbers could be high. The potential for economically damaging infestations to wheat crops is highest in the dark brown and black soil zones.
The silver lining for many producers is that heavy rain earlier in the spring meant many wheat crops were seeded late. Combine that with delayed normal heat unit days and wheat midge may miss some fields.
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“This year everything is delayed so we’re into July before we’re seeing much of an emergence,” said Scott Hartley, Saskatchewan Agriculture’s specialist for insect/vertebrate pest management.
“High heat will probably accelerate things. If midge emerges quickly and crops are not in a susceptible stage, that’s excellent. That’s not good timing for the midge.”
It’s a wait and see game for producers who didn’t plant midge tolerant wheat, said John Gavloski, an entomologist with Manitoba Agriculture.
“For people who seeded quite late, that might be the case, but a lot depends on how many growing degree days the crop and the wheat midge have experienced. It’s a tough question to answer.”
He said midge is appearing in central Manitoba and a high emergence is expected.
The insect appears when an area receives the number of growing degree days that it needs to maintain its life cycle.
“We’ve seen that before, where they miss their opportunity to lay eggs in certain fields,” Gavloski said.
“If the fields aren’t ready, they’re going to keep moving until they find something to lay their eggs into that are ready.”
Hartley said regular field monitoring is key.
Scout in the evenings, from 8 to 10 p.m. when the temperature is around 15 C and the wind is calm or light.
Inspect four or five places in the field for a more accurate count.
Hartley warned against taking action with first midge sightings because the males show up before the egg-laying females.
“Premature spray wouldn’t hit the real target,” he said. “That’s why we emphasize that it’s not when you first see it. Regular monitoring is key to being able to get good control.”
The time between heading and flowering, when the boot swells and the wheat become visible, is the vulnerable stage because the midge can then access the plants to lay eggs. That’s when regular scouting should begin.
Plants are no longer susceptible when they start to enter out or go into flowering. At that point they’ve built up resistance.
Spraying should start in the four days after the economic threshold is reached, depending on the chemical that is used. One adult midge per four to five wheat heads is usually enough to warrant control.
It’s a question of yield verses grade. One midge per four to five wheat heads can decrease yield by 15 percent. Wheat midge larvae can also reduce the grade of wheat, as can more than one midge per eight to 10 wheat heads.
The Canadian Grain Commission limits midge damage in No. 1 CWRS wheat to two percent and eight percent in No. 2. The tolerances are similar in durum.
“We use economic thresholds as a gauge for producers because their systems are all going to be different,” Hartley said. “There may be different varieties; it may predominantly be a CPS grower, or a durum grower. They’ve got to make the final financial decisions themselves.”
