ENTOMOLOGY | Manitoba reported the first-ever cases of western corn rootworm and cannabis aphid this year
There are two new pest insects in Manitoba, according to provincial entomologist John Gavloski.
A seasonal summary of the year’s crop pests, released in mid-November, noted Manitoba’s first cases of western corn rootworm and cannabis aphid in 2021.
Why it matters: Manitoba can add two new insects onto the pest radar after this year.
While western corn rootworm is new, the corn sector is already familiar with its cousin, the northern corn rootworm, which has been established in the province since 2015.
Both species eat away at the integrity of corn roots, leading to issues like harvest difficulty due to lodging.
This year, producers reported fields with lodging and significant rootworm damage (from all species) both near Miami, in central Manitoba, and Souris in the southwest. Of those, Souris reported one of the province’s two western corn rootworm findings. The species was determined to be the dominant type of rootworm in one field where northern corn rootworm was also detected. A single western corn rootworm was also detected through the province’s trap monitoring around Miami.
“Western corn rootworm is actually a very significant finding for anyone who is growing corn consecutively on the same land,” Gavloski said. “Anybody who is growing corn and rotating it, where you’re not growing it continuously on the same land, won’t have a problem with it.”
Rotation is among the most cited management strategies for corn rootworm. Adult beetles lay eggs in late summer, which overwinter and hatch the following spring.
Those larvae “can’t really move too far,” Gavloski said. “If there’s corn where they hatch out, they will get on the roots and feed on the roots and they can do a lot of damage. If there’s no corn where they hatch, they can’t move to where there is corn and they all die.”
The insect is specific to corn feeding, and a gap of even one year between corn crops can therefore cut back a rootworm population, according to a fact sheet published by the Manitoba Crop Alliance.
The same fact sheet — published prior to the finding of western corn rootworm — noted that areas around Souris and the Winkler-Morden areas had confirmed established populations of northern corn rootworm already.
The biggest question, according to Morgan Cott, agronomist with the Manitoba Crop Alliance, lies around any genetic differences between the two species.
“I think the biggest concern is making sure that our products, our seed treatments, our genetics that are coming into Manitoba cover western (corn rootworm) as well, should we need it,” she said.
She added that the insects have been a relatively minor issue so far.
And again, she stressed the need to avoid year after year of corn on the same field, and to rotate crops rather than leaning so heavily on variety genetics. The last thing anyone wants, she noted, is resistance pressure.
Cannabis aphid
A second new pest species might be of concern to hemp growers, should cannabis aphids make it outdoors.
One legal cannabis-growing operation found the aphid in its greenhouse operation in eastern Manitoba this September, the province reported. The operation implemented control measures to beat back the insect after discovering it.
“It is specific to cannabis, so it’s not like it’s going to attack other crops,” Gavloski said.
While hemp could be at risk if the insect became established outdoors, the province reports that the finding is an isolated incident.
“It’s hard to know how widespread this could become in Manitoba,” the entomologist added. “They are good at kind of cuing in on the odours from the cannabis or hemp, so if they were to be outdoors, they certainly could find hemp fields.”
It is unclear, however, how well the pest would tolerate a Manitoba winter, he said.
