Wheat School: Strip spraying can work for grasshopper control

There are well over 100 species of grasshoppers across Canada, but there are four that like cereal crops in particular. Of those four, certain species can dominate a certain region. All of them can make short work of a crop in no time, left unchecked.

John Gavloski, provincial entomologist for Manitoba Agriculture and Resource Development, joins us for this episode of Wheat School to talk about grasshoppers in wheat.

The species of concern for wheat, is the clear-winged grasshopper, who specializes in grasses. “Sometimes it’s a good idea to get to know the dominant species when grasshoppers become numerous because it gives you a clue of what they might be feeding on,” says Gavloski. The two-striped grasshopper seems to be the dominant species in Manitoba this year, so it might change year to year.

Unfortunately, with grasshoppers, there really aren’t any quantitative species-specific thresholds at which to act. “They are a best guess given the information that’s available, but they are general across species,” says Gavloski. For cereal crops, if there are more than eight to 12 per metre square on average, that’s a population that could cause economic damage.

Lots of grassland birds, mammals, and even some reptiles like to eat grasshoppers, so they’re an important part of the food web. There are also beneficial insects that keep grasshopper populations low — the black blister beetle, the ash grey blister beetle, and bee flies are just a few examples.

Grasshoppers thrive under hot dry conditions and there’s a fungal pathogen that can wipe them out if some dampness persists. But, they lay eggs in August and the egg stage is quite resilient, so even if they’ve been submerged in water, those eggs will hatch.

The best way to scout for grasshoppers is to start early, in June, when they’re just starting to hatch. By late June to early July, they’ll be half grown, won’t be able to fly yet and are much easier to control at this point. Try to estimate the approximate population in your cereal crop by visualizing a metre square area in front of you, and trying to count the number of grasshoppers that are jumping around, says Gavloski.

If left unchecked, grasshoppers can really wipe out yield, but on average will be 10 to 20 per cent yield loss, causing the most damage by clipping heads or chewing through stems of the wheat crop. If the number of them is higher, then they could do even more damage.

Control options include bait, insecticides, or by spraying in strips, suggests Gavloski, since most of these insecticides have residual, and because grasshoppers move around quite a bit. This method can help to reduce application cost, too.

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