The battle against Colorado potato beetle is becoming more difficult every season.
It’s not a new problem. As early as 2014, producer groups were already warning that Colorado potato beetles were becoming increasingly resistant to neonicotinoids.
Four years later, the problem has not gone away and, in some patches of the province, has arguably got worse.
High beetle populations made their way into last year’s provincial insect summary, with Manitoba Agriculture noting possible resistance in Titan- and Admire-treated fields.
Some areas of the province now see 2-1/2 cycles of the bug in a season, according to Dr. Vikram Bisht, Manitoba Agriculture potato and horticulture crop pathologist.
“Which is, in Manitoba, unheard of a few years ago,” he said.
Where is the problem?
Reports have been most urgent in south-central Manitoba near Winkler, although Bisht says there have been some issues farther northwest.
Fields near Carberry and Portage la Prairie had adult beetles despite seed or in-furrow treatments, although foliar application knocked them back if they creeped to close to economic thresholds.
“Starting from the western part of our province, which is mainly Carberry-area production, we have reports of increasing adult beetles being found towards the later part of the season, but the incidences or severity is not high enough to warrant foliar application because they appear rather late so they can’t be doing much damage,” Bisht said.
Farmers did have to reach for the foliar insecticide near Portage la Prairie.
Fields near Winkler, however, have seen beetles brush off a long line of both new and established chemistries.
“There are more insecticides being tried with little success,” Bisht said. “The major portion of southern Manitoba is a hot spot, I would say, for what’s going on.”
Those reports match results from a three-year trial run by Peak of the Market in the Winkler area.
Dr. Tracy Shinners-Carnelley, vice-president of research and quality with Peak of the Market, says they have noticed more pressure in the spring from overwintering adult beetles and a shorter period of neonicotinoid control.
The three-year study tested four products; Titan, Actara, Minecto Duo and Verimark, a non-neonicotinoid product that the industry hoped might provide some relief as regulations on “neonics” tighten.
The study, however, found that Verimark control appeared to break by July in all years, while neonicotinoid treatments provided control until up to mid-July or later.
The same three-year research found that seed treatment lasted longer than if the same products were used in furrow and that higher-rate applications gave the longest window of control.
The researchers had to turn to foliar treatments as larvae and defoliation reached economic thresholds, however.
Delegate and Exirel, the two foliar products tested, still took the population to near nothing, according to study results.
Shinners-Carnelley, however, has been warning farmers off overuse of Delegate for fear of resistance pressure. Manitoba Agriculture also urges growers to rotate chemistries and to avoid using the same active ingredient for seed treatment and foliar application.
Crop rotation can be effective to manage the pest, Bisht said, but added that it is not enough to switch potatoes onto the next field.
“That’s where the beetles can easily walk,” he said, but admitted that keeping that distance may not be practical for farmers every year.
Beetles have been taking longer to emerge in spring, Shinners-Carnelley also noted, making it harder to target a specific growth stage, since development is spaced out.
“They’ll start around the time when the potato crop is emerging, which is often end of May, early June and it used to just take a couple of weeks,” she said. “But now what we’re seeing is that prolonged emergence even right into July.”
At the same time, according to Dr. Russell Groves, entomology professor at the University of Wisconsin who spoke at the 2018 Manitoba Potato Production Days, many newer products are most effective against a particular growth stage.
“Which tools you choose dictates your timing,” he said. “These reduced-risk, age-specific insecticides have to be focused on your appropriate life stage… each one of them requires a different timing. Once it’s time to go you’re probably going to start and you’re going to put on at least three successive applications to get control.”
It’s a management challenge in a field that might have beetles at multiple life stages at the same time.
“It’s kind of like we really need to relearn what is happening with the life cycle and then figure out how to best proceed with those available tools that we have in such a way that they’re going to work and be effective but also to keep them around,” Shinners-Carnelley said. “We don’t want to be doing any practices that are going to decrease the length of time it’s going to take for those beetles to develop resistance.”
‘We are in a bind’
Regulatory issues add another dimension to the fight.
Environmentalists and beekeepers have argued strongly against neonicotinoid use, arguing that they devastate pollinator populations.
The fate of the neonicotinoid imidacloprid, or Admire, is currently in the hands of Health Canada’s Pest Management Regulatory Agency. The PMRA is considering deregistering the chemical for agriculture and phasing it out over three to five years and is expected to make a final decision by the end of 2018.
Clothianidin and thiamethoxam were also put in the hot seat last year when Health Canada announced special reviews. The agency ultimately proposed to maintain both products’ registration, but put conditions on application and plans to phase them out for certain aspects of agriculture, like foliar applications in orchards. Those decisions are also up for public comment.
For the potato farmer however, “neonics” have been their best weapon against Colorado potato beetle and have no easy substitution.
Companies are looking for new products, Bisht said, while Shinners-Carnelley earmarked a long list of incoming research on beetle management options.
“It’s a very bleak outlook right at this present time,” she said. “There’s a lot of moving parts when we look at where do we go in the future with beetles. Like mentioned, we see the changes in behaviour; we know there’s resistance issues, but we also know there’s some major regulatory hurdles upon us with the current products that we have. We need to look at what is coming down the road in terms of new opportunities and new ways of looking. We really want this research to move forward so that we can get that going in the right direction, but it takes time.”