Be on the lookout for three early-season crop pests

MAFRD entomologist John Gavloski has advice on flea beetles, 
cutworms and wireworms for Manitoba farmers

Be on the lookout for flea beetles, cutworms and wireworms, all of which can take a bite out of yields early in the growing season, says John Gavloski, entomologist with Manitoba Agriculture, Food and Rural Development (MAFRD).

Canola is especially vulnerable to flea beetle damage during the cotyledon to second true-leaf stage, Gavloski said during MAFRD’s Eastman webinar May 14.

“Most people have concluded once you have three to four true leaves on a plant, the plant can usually do a good job in compensating for the flea beetle feeding,” he said. “You really need to protect the plants when they are in that cotyledon to first and second true-leaf stage. Those stages of the plant have a harder time compensating from the shot-hole feeding and there’s not enough plant tissue there yet for the plant to respond.

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Some fields have been complete writeoffs forcing farmers to reseed.

The economic injury level for spraying flea beetles is about 50 per cent damage. But because damage can happen so quickly farmers are advised to consider applying a foliar insecticide at around 25 per cent damage, Gavloski said.

Seed treatments usually provide about three weeks of protection after seeding and sometimes up to four weeks, depending on conditions.

Seed treatments are more effective under dry, warm conditions than when it’s cool and wet.

There are more than 70 species of flea beetles in Manitoba, 10 of which eat canola, but it’s the striped and crucifer that do the most damage. The striped flea beetle, which has yellow stripes on its back, attacks earlier; crucifer shows up a little later.

“Usually by late May and early June, crucifer becomes the dominant flea beetle and that’s the one that typically does the most damage here,” Gavloski said.

The insecticidal seed treatments Helix and Prosper will kill both species of flea beetles, but are slightly more effective against crucifer flea beetles, he said.

Since bigger canola plants are better able to withstand flea beetle feeding, techniques aimed at getting canola to that stage faster are helpful, including shallow seeding. Research has also shown flea beetles do more damage in conventionally tilled fields than in zero till.

Flea beetles overwinter outside of fields in leaf clutter and plant debris and start flying when temperatures hit 14 C, although their movement is restricted on windy days. They’ll still feed on canola plants then, including the underside of leaves and on stems.

crop chart of insect damage

Cutworms

Cutworms can damage many different crops, including canola. Lumiderm is a canola seed treatment that includes either Helix or Prosper, plus cyantranilipole, which controls cutworms, Gavloski said.

The redbacked cutworm, which has red lines down its back, is the most common type found in Manitoba. It overwinters as an egg, emerging in late May or early June, usually causing patch damage. Farmers should scout their fields thoroughly and not assume an entire field is infested with cutworms.

The darksided cutworm, which has grey stripes, causes similar damage.

Wireworms

“It seems to be hit and miss in Manitoba as to whether they are an issue or not,” he said.

“We’ve had localized areas with problems over the past few years.”

Some corn has been damaged by wireworms in the Steinbach-Niverville area.

Wireworms do all their damage below the soil surface attacking seeds and new growth.

Seed treatments are the means of preventing wireworm damage and they only repel the pest rather than kill it, Gavloski said.

Cruiser and Stress Shield are wireworm seed treatments for cereals and pulse crops. Cruiser can also be used on sunflowers.

Some wireworm seed treatments boost seedling vigour, but only when the crop is under stress, he said.

Boosting the seeding rate can offset some wireworm damage, but the extra cost needs to be considered.

Getting crops out of the ground quickly by seeding shallowly into warm soil can help too.

Wireworms have some natural enemies, including ground and rove beetles, Therevid larvae, some species of nematodes, and the fungus Metarhizium anisoploae.

As of last week diamondback moth counts were low in Manitoba, Gavlsoki said. The pest, which can damage canola crops, mainly blows in from the United States.

About the author

Reporter

Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.

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