Swede midge threat looms over Manitoba canola crops

A deceptively tiny bug can wreak non-stop havoc in canola

Midge larvae in a vial.

If you thought clubroot was scary, get ready for Swede midge — a voracious mosquito-like bug that can wreak havoc with your canola yields.

First found in North America in 2000, and has appeared in low numbers in Manitoba in 2007 and 2013, said Julie Soroka, a Saskatoon-based entomologist with Agriculture and Agri-Food Canada.

“The most I’ve ever caught is five adult males, but if we ever get the numbers that Ontario has got, we’ll have to start growing alfalfa for hay because there’s probably more profit in it,” said Soroka, in a presentation on emerging canola pests at the recent CanoLAB 2014.

So tiny that it looks like it couldn’t hurt a fly, in Ontario the cousin to wheat midge is causing such havoc that many farmers there have given up on canola due to devastating losses.

Unlike its cousin, Swede midge can go through as many as five generations in a single growing season and overwinter in the soil anywhere in Canada where canola is grown.

Wet weather

Like its cousin, the bug emerges only in wet weather. The males only live for a day, but the females hang around for a couple more days — long enough to lay a few hundred eggs on the growing points of plants such as leaves, buds and flowers.

The minuscule sap-sipping larvae do the most damage, but it depends mainly on when they start feeding. The earlier they appear, the more damage they cause.

“If you have heavy damage before bolting, you can actually have total destruction of your seed potential,” said Soroka, adding that the flowers turn into “bottles” that never open.

Swede midge is nearly impossible to control chemically. Adults are weak fliers, but they are often blown in from other areas. Also, because they only live for a few days, detection and spraying effectively is very difficult.

More from the Manitoba Co-operator website: Prairie grasshopper populations expected to rise in some areas

In the soil

"If you have heavy damage before bolting, you can actually have total destruction of your seed potential," Julie Soroka. photo: Daniel Winters

Once in the pupae stage in the soil, there’s no effective solution, she added.

“Canola is susceptible for a long period of time. It’s not like wheat, where once wheat has passed the growth stage, the midges are gone,” said Soroka.

Early seeding helps the canola to get a head start on the bug and heavier seeding rates may offer a dilution effect.

In Sweden, farmers have learned to cope with the bug by working together. By synchronizing their cropping plans, and only planting canola once out of every four years, they find that it can be outmanoeuvred, she added.

However, their canola acreage is much lower than here, and they often use mouldboard plows to bury the insect pupae in the soil, a strategy that Soroka said is very effective.

The good news is that the bug can’t thrive under dry conditions, but the bad news is that it can hang around for another year. Even worse is the fact that biological control agents or natural enemies of the critter in Canada are “zero, zippo, nil.”

Cabbage seed pod weevil is another reason to avoid tight canola rotations, but unlike Swede midge it can be effectively controlled with insecticides.

MAFRD entomologist John Gavloski said that the top three insect pests for canola this year are flea beetles, grasshoppers and possibly cutworms depending on winterkill. Diamondback moths and other airborne bugs are impossible to predict, however.

“The two that I think people should be at least watching for and maybe anticipating are flea beetles and if we get a hot, dry year, grasshoppers,” said Gavloski.

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