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Unearth the pests lurking in your soil

No clipped-off plants yet? You may still have cutworms

You’ll need to get your hands a little dirty.

Otherwise you may have no idea what’s about to chomp your crop — until it’s too late.

John Gavloski, Manitoba Agriculture entomologist, says farmers should watch for cutworm and wireworm damage, something that, in both cases, will require digging in the soil around plants.

The three most common cutworms may be out and hungry, Gavloski warned, although the two main “clipping” species, infamous for gnawing through stalks near the ground and stopping a plant’s development in its tracks, are likely still small.

Both redbacked and darksided cutworms overwinter as eggs and begin development from scratch come spring, according to Gavloski.

“Smaller larvae, you have to look a bit harder to find them,” he advised, adding that they may be taking more chunks out of cotyledons at the moment rather than the clipping they are better known for later in the season.

The two species are separate from another, the dingy cutworm, both in colour and development. While the redbacked and darksided cutworm, true to their names, sport reddish stripes down the back or dark stripes along the side, the dingy cutworm sports a dull colouring and markings that Gavloski describes as V-like tire tracks.

The species also overwinters as larvae, not eggs, he added.

“By June, the other species are catching up, but at this time of year, likely dingy cutworms are going to be a bit bigger than the redbacked and the darksided,” Gavloski said. “They rarely will cut plants, even when they’re bigger. This is what we call a climbing cutworm. Climbing cutworms don’t do a lot of clipping. They prefer to climb on plants and chomp away at them. They will eat small plants right to the ground if the plants are tiny enough.”

That defoliation may confuse farmers who normally connect cutworms with clipping, he said.

Farmers may have to adjust how deep they dig when scouting for the pests, depending on the last rainfall, according to Manitoba Agriculture. Cutworms are closer to the surface in moist dirt, while dry conditions, like the province endured earlier this spring, can send them up to four inches into the soil.

Farmers may also be able to dodge spraying the whole field, given usual cutworm patterns.

“Sometimes you have a 10-, 20-, 30-acre patch that has a lot and the rest of the field, not so much,” Gavloski said. “Often this is the result of their egg-laying patterns the previous fall or late summer. If there’s a weed patch in the field, that could draw them to a certain part of the field. A later-flowering portion of the field, that could also do it.”

Patches can then be spot treated rather than a blanket application.

Wireworms

The surface-feeding cutworms should not be confused with a wireworm problem, although farmers may risk mistaking the beetle larvae for cutworms.

The underground pests feed on roots and seeds rather than foliage and stems that draw cutworms, Manitoba Agriculture says, although the nocturnal cutworms may also be underground during scouting in the day.

The beetle larvae, however, appear harder, may be longer, and unlike cutworms, have no “proto-legs” midway down the body.

Wireworms dug out of a wheat field near Teulon in 2007.
photo: Manitoba Agriculture

“You can’t use foliar sprays on wireworms. It would not work,” Gavloski said. “Again, they don’t come above the ground. It’s a matter of knowing from year to year what your levels are like. If you know you’ve got fields with potentially higher levels, seed treatments will minimize the feeding. The seed treatments that are out there right now don’t necessarily kill the wireworms, but they kind of make them sick and they don’t feed on the plants as much.”

Look-alikes

Farmers may want to take a second look at that worm they just dug up.

Both wireworms and cutworms are an economic concern, but Gavloski stressed that a list of other worm-like organisms are often mistaken for the pests, all of which pose no threat to the crop or, in some cases, the farmer might actively want to keep around.

Therevid, or stiletto fly, larvae might be mistaken for wireworms, Manitoba Agriculture’s wireworm information sheet warns, although the pale larvae are, in fact, predators.

“They’re very quick, so they will wiggle around in the soil quite rapidly when you disturb them,” Gavloski said. “If you pull up something that kind of looks wireworm-like in shape but it has absolutely no legs and is very active, wiggles rapidly when you disturb it, that’s a therevid larvae. They feed on wireworms and possibly cutworms, so those are good insects. You want those in your soil.”

The tiny and almost transparent enchytraeid worm should, likewise, be overlooked, he said, since the worm is a decomposer feeding on bacteria and fungi and poses no threat.

About the author

Reporter

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.

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