Guenther: Cutworms eye new Prairie soybean acres

Some soybean growers in Saskatchewan’s southeastern corner are dealing with unwelcome dinner guests.

Brad Eggum, of Eggum Seed Sales, was scouting a soybean field when he came across cutworms by chance.

“The beans were struggling to get through and we were just checking the emergence and started finding (cutworms),” says Eggum, who farms near Halbrite, Sask., about 150 km southeast of Regina.

Cutworms devour plants at night and burrow into the soil during the day. By digging around damaged plants, farmers and agronomists have uncovered the pests.

Saskatchewan soybean growers aren’t the only ones dealing with cutworms. Shawn Rempel, product manager with Quarry Seed, said he’s received a few calls from people between Weyburn, Sask. and Virden, Man.

“But I think the problem is that guys are not used to scouting for them in soybeans,” said Rempel. Farmers are finding them while spraying, he added.

Todd Walker, western rep for Thunder Seeds and Quarry Seeds, says cutworm numbers are down the last few years.

Walker, based out of Souris, Man., said he’s rarely seen cutworms that needed to be controlled in soybean fields in the last nine years.

“But they’re out there. You’ve just got to be aware and check your fields regularly for them,” he said.

Cutworms are more likely to show up in lighter soils and on south-facing slopes. “They like to lay their eggs in loose soil,” said Eggum.

Walker said farmers should check the whole field while scouting for cutworms, rather than sticking to field edges.

Manitoba Agriculture, Food and Rural Development’s latest crop report notes redbacked and dingy cutworms will soon pupate. Generally, it’s not worth spraying if most cutworms are an inch or longer, as they’ll soon pupate, the report states. But if numbers are very high, control might be necessary.

As a rule of thumb, “if you’re out there during the day and you’re finding cutworms during the day quite easily, you have a problem,” said Rempel.

Seed treatments will initially protect soybeans from cutworms. But as the plants grow and the seed treatments wear off, farmers may need to hit cutworms with another insecticide.

Generally farmers can tank-mix insecticides with the first pass of glyphosate, though they should always check labels. Farmers should spray for cutworms in the late evening, said Walker. “So you want that residual on the ground when they come up to feed. And it usually lasts a couple days, (depending) on the weather.”

Soybeans are a Cinderella crop, said Rempel. “You just let them grow and spray Roundup on them. A lot of guys are understanding now that, just like every other crop, it does pay to scout and see what’s going on out there.”

–Lisa Guenther is a field editor for Grainews at Livelong, Sask. Folow her at @LtoG on Twitter.

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