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Ont. farmers should wait to spray for WBC

Ont. farmers should wait to spray for WBC

Spraying during silking and peak flight maximizes the amount of eggs and larvae controlled 

By Jackie Clark
Staff Writer 

Data from western bean cutworm (WBC) traps indicate that numbers are low compared to previous years, but still increasing. Farmers should hold off on spraying, according to experts from the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). 

“We’re still early, so managing things right now is premature and it’s not going to be as effective as if we wait until closer to peak flight,” Tracey Baute, OMAFRA entomologist, told 

“Moth counts are climbing in traps, but we still anticipate another week or two before we see peak flight, which also means peak egg laying,” she explained.

OMAFRA data shows that peak week for WBC typically occurs around July 29-Aug 4.

To time control more effectively, farmers should “focus in on crop stage,” she added. 

Initially, WBC researchers in the Midwestern U.S. said that spraying pre-tassel or early R1 was ideal timing. However, “now that it’s in the Great Lakes area, it’s really more of a concern with DON and ear mould issues,” Baute said. WBC don’t tend to impact corn yield from direct feeding, however the wounds they create increase mould risk. 

2021 is already shaping up to be a high-risk year for ear mould. 

“In low mould years we tend to see that WBC is the contributor,” Baute explained. “With ideal weather conditions lining up for ear mold, it’s even more important for (producers) to line up their fungicide properly, but also take WBC into account.

Farmers “need to hold off and spray a little closer into R2, but not R3 when you’re seeing the brown silk, to try and get as many larvae that are going to be on the plant during that time before they’re in the ear,” she said. Eggs take around a week to hatch, and probably another week before they’re down in the ear, so that delay in timing allows farmers to spray the most possible eggs and larvae on the plants, before R3. 

“That’s why we’re trying to persuade people to hold off and spray just a little bit later,” she added. “It’s likely even better timing for ear mould fungicides too, so you can do both at once if need be.”

Similarly, in dry beans producers should also hold off until peak flight to spray.

Producers should wait to spray “until you at least have pods on the plants, because that is really what they’re going to go for,” Baute explained. 

In either crop, only spray if you are reaching threshold, she said. Producers should scout, starting with most advanced fields, every 5 days. If 5% of plants have eggs after three scouting trips, threshold has been reached. 

WBC “has a high chance of developing resistance to any of these foliars that we’re applying, so we want to use them wisely. Any applications ‘just in case’ are really not sound IPM,” Baute explained. Protecting against resistance involves “rotating all of the tools, and that includes the VIP3A hybrids.”

Research from the University of Guelph Ridetown “indicates a potential for resistance, so we do need to rotate our VIP3As and our chemistries,” she said. “I know some have a favourable go-to for insecticides and I’m worried that … if everyone is using that one all the time, we really risk losing it as an option.” 

Tracey Baute photo

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