More than cutworms “bugged” corn crops in 2017

Pests in 2017 have been a more complicated picture, based largely on a mixed bag of weather-related challenges

Seed dealers, agronomists and advisers are very vocal in 2017 about scouting for Western bean cutworm egg masses.

Coming out of winter and looking ahead to any growing season, it’s impossible to predict which insect pests will be the biggest challenge for growers. In 2001, for instance, soybean aphids first became a widespread issue for Ontario farmers, and the fear took such firm root that we’d have to deal with them in 2002 that the reality fell short of the expectation, leading to the incorrect assumption that aphids would be an “every-other-year” pest.

For the past two years, Western bean cutworm (WBC) has become a focal point for farmers, agronomists, extension personnel, retailers and researchers. In the U.S., farm media reports were urging growers to use increased diligence in steeling against its impacts, even as Can­adian farmers waited for their fields to dry out and warm up.

In spite of increased awareness and calls for increased scouting, the one truism about insect problems is that a pest will be a problem when it becomes a problem. For much of the early part of the 2017 growing season, most agronomists, advisers and ministry personnel took more of a wait-and-see approach, yet with corresponding words of caution.

Tracey Baute, field crop entomologist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), took a proactive step on May 10, issuing a fact sheet on WBC titled “How to prepare for 2017.” She noted that WBC “has earned the designation of primary pest of corn in Ontario, and it is starting to become important for dry bean growers, too.” She also co-authored a fact sheet (“Western bean cutworm scouting and management in field corn”) with Jocelyn Smith and Art Schaafsma, both of the University of Guelph Ridgetown Campus.

But 2017, with its heavy rains interspersed with patchy dry regions, has been an ideal environment for almost every pest, notes Baute, with some regions seeing species that under normal circumstances, a farmer might not worry about.

“If anything does have us at a bit of disadvantage, it’s that the crops got in a little later,” she adds. “That can set us up for certain insects to build up their populations and hang out in fields longer before the crops are harvested. That said, weather will play a big role as to whether they have an impact.”

Appearances can be deceiving

During the first half of July, Twitter came alive with reports, photos and posts pertaining to WBC activity and counts. In one week (July 10 to 17), trap-counts in southwestern Oxford County skyrocketed, from 55 collected near the hamlet of Cultus to 366 seven days later. During the same period, a farm near Walsingham jumped from 71 on the 10th to 263 on the 17th.

Granted, these numbers were from one small corner of one county, but this certainly wasn’t the only part of the region to see more activity.

Spraying is warranted if there’s an accumulation of five per cent of plants with eggs or small larvae, according to OMAFRA recommendations. photo: Aaron Stevanus, Pride Seeds

In spite of those higher counts, Baute reminds growers that there’s more to determining the severity of pests or their potential for damage. In her “How to prepare for 2017” document, she noted that it’s the action threshold that is the key factor to determine whether to spray or not. For starters, thresholds are not based on trap counts, since only the males are caught in traps, leaving the females free to lay eggs.

“Spray is warranted if there has been an accumulation of five per cent of the plants with eggs or small larvae,” states Baute’s document. “If during Scouting Trip 1, there were two per cent of the plants with eggs on them, and four days later during Scouting Trip 2, there are three per cent, then there’s a need to spray.”

Regardless of rising trap numbers, Baute says scouting is the real key. For the 2017 growing season, she advised all growers to scout all corn hybrids, including those containing Bt technology. Those hybrids with the Cry1F gene are no longer effective against WBC. Even those with Viptera technology should be scouted to confirm the Bt trait is still effective.

John Seliga, an agronomist for DuPont Pioneer, echoes many of Baute’s observations, including her advice about scouting for WBC. He also has been active on Twitter, posting photos of egg masses and tips on how to use sunlight and shading to find them. In his area along the Lake Erie shoreline, he’s hearing of WBC trap counts as high as 300 in a week. That’s why he also advocates scouting as one method of monitoring, and yes, the Cry1F genetic trait is less effective.

“Hybrids containing Viptera technology still benefit from very good protection to this pest, though there are relatively few options available for growers today,” says Seliga. “With regards to scouting, I believe what the Corn Pest Coalition group has set up is a highly effective network of Western bean cutworm traps for Ontario producers. It’s critical to monitor moth flights to accurately predict when field scouting should occur.”

With proper scouting, growers and their agronomists can better plan an effective insecticide management strategy to control WBC and protect the corn crop from both yield and quality losses, Seliga adds.

Other pests in the mix

One of the drawbacks of paying particular attention to one pest is that others might escape notice — although to be fair, increased scouting should limit that potential. Drew Thompson, market development agronomist with Pride Seeds, says soil insects are at extremely high levels in 2017, including grubs, wireworms and seed corn maggot, among others. Increases in the grubs and wireworms suggest a link to recent mild winters, along with low winter mortality rates. Why seed corn maggot is a problem is something that needs answering, yet it’s the worst Thompson has seen.

“Cover crops definitely hurt,” says Thomp­son, adding that early pest pressures were varied. “Slugs and millipedes were bad, some soybeans needed to be replanted as a result of slug pressure. Bean leaf beetle was found in the Niagara area, and some guys did end up spraying.”

That’s the first of bean leaf beetle in Niagara that Thompson has witnessed, but in talking to other agronomists from the region, the pests are not unheard of in that area. Black cutworm was also quite common, and armyworm was patchy, although some wheat and corn fields required early control.

Baute and Seliga also note an increase in other pests, particularly soybean aphids. Baute mentions that some growers she’s talked with were shocked to find them as early as June.

“They’ve forgotten that it’s very normal to find them starting colonies anywhere east and north of London,” says Baute. “It by no means indicates that this year will be a problem year.”

For Seliga, 2017 will be known as the year that growers had to deal with above-average pest pressures for below-ground insects that are a concern at the seedling stage. It’s still too early know the total rootworm damage.

The U.S. Corn Belt has reported finding the pest, and there had been sporadic reports in Ontario. But Seliga believes longer rotations are a boon to growers in Eastern Canada, and should help control corn rootworm from establishing with the same intensity.

This article originally appeared in the September 2017 issue of the Corn Guide.

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Ralph Pearce

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