Will western bean cutworm (WBC) be to 2019 what DON was to 2018? According to the evidence thus far, probably not. In fact, WBC appears sparser than expected.
That said, Tracey Baute, field crop entomologist and WBC expert with the Ontario Ministry of Agriculture, Food and Rural Affairs, says several factors have combined to make accurate impact predictions difficult.
Why it matters: Planting delays experienced in the first half of 2019 mean crops are developing when WBC is at its most aggressive. Negative impacts could be seen despite current low pest numbers.
Crop development ill-timed
Ineffective pheromone lures in some of the traps used in the WBC trap monitoring were a problem early in the growing season. Some traps worked fine, says Baute, while others did not effectively attract migrating moths, making it difficult to draw accurate population estimates.
“That added an additional issue with us comparing previous years [ …] It got sorted out before we reached peak flight,” she says.
Slow growth early in the planting season also meant the WBC trap network, as described by Baute in an article for Field Crop News, did not reveal its first moth until the second week of July — a time normally considered close to WBC’s peak flight period.
However, Baute says the main danger in 2019 stems from late planting. Corn and dry bean crop development now line up with WBC development, posing a greater risk of damage from both the pest itself and the diseases following in its wake — notably DON and other fungal pathogens.
“They may not have as long a time to feed on the ears as in some years. They didn’t really get in the fields until August,” says Baute, but some ear feeding may have gone unnoticed thus far.
“There’s always going to be feeding even if they spray. There will be some that survive,” Baute says. “Damage really doesn’t show up until defoliation of the plant.”
She also reiterates no clear hot-spots have been identified yet, but the aligning of WBC and crop development means moths can pick and choose their locations more easily. Rising yearly temperatures also allow the pest to overwinter closer to Ontario, giving it yet more flexibility within the province.
“[This] also highlights not to rely on trap counts. You still have to scout because the dynamics of what’s going on in the field could be different then what the trap is telling you,” she says.
Unknown factors might be suppressing WBC
WBC numbers have been shifting downwards over the last two years. Indeed, Baute says both the number of egg masses and the remnants of egg masses have dropped. This indicates something is affecting the ability of WBC to lay eggs.
“We are not sure […] We’re just not seeing the egg masses as prevalent as we usually do. It’s an effort to find enough compared to previous years,” she says. “If you scout frequently enough you should still see the presence of egg masses. In some cases, they weren’t there.”
For her part, Baute believes the missing factor is likely greater pressure from bio controls – namely predatory insects such as ladybugs, lacewings, and others. However, more investigation is required.
Earworm numbers rising
While western bean cutworm numbers appear to be dropping, the last few years have brought an increase in corn earworm populations. This pest comes from the United States and lays its eggs directly on ear silk, which Baute says makes them very difficult to see.
As with WBC, the late 2019 planting season also provides greater opportunity for the pest to develop.
“That’s another pest that’s likely going to start playing a role in ear damage in the fall. I think we’re going to see it more often,” she says. “It’s not just a sweet corn issue anymore […] If we have years where we delay grain corn planting, we are going to see more risk.”