Resistance Management Key To Maintaining CPB Control

Manitoba potato growers have used a lot of Group 4A neonicotinoid in-furrow treatments over the past few years – and for good reasons.

They work, they’re easy to use, application is made at planting which regularly gives full-season control and compared to some of the newer alternatives, they’re affordable.

With that package in hand, the real question might be something along the lines of “Why in the world would a potato grower choose anything else?”

For the answer to that question, it’s necessary to take a trip back to the future. About 15 years ago, the first neonicotinoid product, Bayer’s Admire, provided economical broad-spectrum control of significant potato pests, most importantly Colorado potato beetles.

Since many of the existing products had been on the market for many years and were beginning to break down as the pests responded to repeated applications as they inevitably always do – by developing resistance, particularly in CPB. By the time Admire hit the market, most of the other products had been rendered impotent by the evolving insect populations.

But that reality has translated into another reality – almost complete reliance on products like Admire and other brand names in the same chemical family.

Brent Elliot, an entomologist with Manitoba Agriculture, says the neonicotinoids aren’t immune to this resistance process, and the fact that they’re as widely used as they are makes a repeat of the familiar pattern more and more likely with each passing year.

“In other (potato) production areas, they started seeing resistance very early,” Elliot says. “We know that most of our crop is treated with infurrow neonicotinoids, so we know that the selection pressure is there.”

No one is exactly sure why Manitoba’s potato-growing region hasn’t been affected as quickly as other growing areas. Some speculate it’s because we have relatively isolated growing areas that are more spread out than other regions. Others point to the fact that Manitoba hasn’t been using the product quite as long. But one thing that’s simply not on the radar is the possibility that Manitoba potato growers are going to get a pass from the hard scientific reality of selection pressure.

“It’s not an if, it’s a when,” says Elliot.

That’s meant a growing emphasis on continuing to practise careful stewardship of the neonicotinoid products, says another potato specialist who’s done a lot of work on crop protection products. Darin Gibson, a research agronomist with Gaia Consulting, says there’s a strong incentive for growers to protect these products.

“The three new ones (see sidebar) aren’t quite as strong,” Gibson says.

The neonicotinoids are also cheaper and are in-furrow applications, rather than foliar applications. For an intensive crop like potatoes every trip across the field by a sprayer that’s eliminated or prevented makes the industry a better neighbour – and less of a lightning rod for any potential backlash against agriculture practices.

Best management practices for maintaining the efficacy of a crop protection product are fairly straightforward. The most important is rotation – both of the potato fields, to ensure the same populations of potato beetles aren’t being treated year after year and between chemical groups, to ensure that when they are treated, it isn’t with the same mode of action.

It’s especially troubling if there’s a second foliar application of a Group 4A product made towards the end of a growing season when the infurrow application begins to run out of steam.

“They need to come back with a different class of foliar,” says Gibson. “Going back in with another neonicotinoid is something you should never do, it speeds up the development of resistance.”

By taking these precautions, growers can probably stretch out the useful life of the Group 4A products for a few more seasons – but even the best precautions aren’t likely to save it forever. There are likely already resistant populations, which can occur naturally, but selection pressure has not yet been high enough to bring them out.

“I’m not saying we do have a problem – we may not – but to say it’s not an issue, I don’t want to go that far,” Gibson says.

Elliot says growers may be taking some comfort from the fact that a recent national study that looked at samples sent to a national diagnostic lab showed Group 4A resistance in Eastern Canada, but not Manitoba. But he says the plain and simple truth is that the problem isn’t being found because nobody’s looking very vigorously for it.

“There was only one sample sent to Ontario (for testing for resistance),” Elliot says. “We just can’t get enough samples (to know if resistance is present).”

Elliot says he’s asking growers who have any doubts whatsoever to collect samples or give him a call to report the potential issue.

“We’d like to get out and get it tested,” he says.

About the author

Editor

Gord Gilmour

Gord Gilmour is Editor of the Manitoba Co-operator.

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