Owen Olfert, entomologist with Agriculture and Agri-Food Canada in Saskatoon, says the midge risk is elevated for much of Saskatchewan and into Alberta. “Conditions for ovipositioning — egg laying — have been ideal for the past two years,” he says.
On top of that, parasitism by midge enemy No. 1 — our friend the mini Macroglenes penetrans wasp — is down. Normally we would see 30 to 35 per cent of the midge population wiped out by its natural enemy, but the parasitism rate was only about 24 per cent last year, Olfert says. “Midge populations are certainly increased for 2008,” he says. “Which will be a cause for concern for producers.”
John Gavloski, provincial entomologist for Manitoba, says populations seem to be up in Manitoba, too. “Be on the lookout for midge,” he says.
So what do you do?
- Your control target is the adults. They start emerging late June and early July and populations usually peak in the second or third week of July. They lay eggs in emerging wheat heads. So, if your wheat is between heading and flowering when adult midge populations are above the economic threshold, then you may want to spray.
- To find out the midge population in your fields at this critical stage, you can either listen to entomologists and agronomists, or you can do your own scouting. “People hate scouting for midge,” Gavloski says. That’s because midge don’t fly during the daytime. They start flying around the canopy — and laying eggs in heads — in the late evening and at night. So scouting starts at about 9 p.m.
- You are looking for an orange flying insect about half the size of a mosquito. Note that during the day you will often find yellow lauxanid flies in wheat fields. These look more like flies than mosquitos, and they fly during the day — a key indicator that they are not midge. Don’t bother spraying for these flies. They are harmless to the crop.
- The old economic threshold said to spray if you see one adult per four or five wheat heads. That threshold has been modified somewhat. If you want to protect yield only, stick with the one midge per four or five heads threshold. If you want to protect yield and a No.1 grade, spray if you see one midge per eight to 10 heads during the susceptible stage of the wheat.
- If you choose to spray, do it late in the evening. As noted, that’s when the adults are flying. “Early morning can also work,” Gavloski says, “but midge don’t hang around very long after the sun comes up.”
- Products registered for midge should protect wheat heads for several days. It would be ideal if insecticides could also move systemically into the wheat head and kill larvae feeding on the kernels, but nothing seems to work that way on midge, Gavloski says. So the adults and possibly the eggs are what you are killing with the insecticide.
- Once wheat is flowering, you don’t have to spray for midge. By that time, the wheat plant is producing its own natural pesticide that fends off midge. An insecticide application at this time is not needed and can potentially cause more harm than good by killing off natural enemies that would normally help keep wheat midge and other potential pests in check. Many farmers may be lucky and find their wheat already flowering by the time wheat midge populations start to build up in July, Gavloski says.