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Natural pest control still a challenge

Pest control in potatoes is caught between growing pressure to cut back on common chemical tools and concerns over chemical rotation, but do biopesticides factor into the path forward?

Potato biopesticides are still digging a niche in a sector beleaguered by chemical-resistance concerns, social pressure and the threat of regulatory crackdown on common chemistries.

But their best fit might support, rather than replace, what growers are already doing in the field.

The promise of biopesticides — drawn from naturally occurring substances that are unfriendly to insect threats or pathogens like root rots — is intriguing to a sector trying to spread out chemical rotations (and therefore extend the life of some of those chemistries) while prepared for regulatory changes on products like mancozeb, one of several chemicals currently under Health Canada’s eye.

“Things are changing with biopesticides,” Darin Gibson, president of Gaia Consulting said. “In the past, they tended to not work very well. The efficacy of some of these products are definitely improving and so I could see in the future where there’s going to be more of these biofungicides as part of a program.”

That day, however, is still a ways off, he cautioned. Gibson doubts that biopesticides have developed to a point that the sector can significantly cut back on its conventional tools, while the products may still be several years away from being commonly used in commercial production.

Leonard Rossnagel, retired Manitoba potato agronomist and former director with the Manitoba Seed Potato Growers Association, says biopesticides have garnered attention from the big names in the agro-chemical’s market. Those companies are putting research dollars into biopesticides, he said, while some biocontrol products have made a foothold in the market.

Both organic and conventional growers regularly use the soil bacteria-based spinosad biopes­ticides, he said, while products like the biofungicide Serenade SOIL have been launched in recent years to suppress root rots like fusarium, phytophthora and pythium, as well as diseases like rhizoctonia and black scurf.

Where’s the fit?

Amanda Gevens, professor of plant pathology at the University of Wisconsin-Madison, argues that anyone expecting biofungicides to completely replace conventional products may be barking up the wrong tree.

Instead, Gevens sees biofungicides as something best added to an existing program, in the name of disease prevention and chemical rotation.

The nature of biofungicides makes them more preventive, since they have to build in the soil or be primed prior to infection to be effective, Gevens said, and a field with more than moderate disease pressure is unlikely to see benefit.

Amanda Gevens.
photo: Alexis Stockford

“It’s a microbial and the population has to establish viability or it’s a compound that’s eliciting resistance in the plant,” she said.

Field history and production region may also shift how the farmer should approach integrating a biofungicide, Gevens said, and soil type may determine if a biological agent is an option at all.

“To use an example, in central Wisconsin we have very sandy soils and the bulk of our potato production is happening on these soils with very low organic matter and we know that incorporating microbes, if we want to establish beneficial microbes, they don’t do so well in that environment. So growers do have to have a basic understanding of their soil type and the likelihood that, at least the microbial-based pesticides, will actually take up residency there and do what it is that they are expected to do as fungicides.”

Producers should not, however, expect a big drop in input costs. Biopesticides are not cheap, Gibson warned.

“Potentially some of those products could either be as a tank mix where you can reduce your rates of conventional products or you could alternate with some of these biofungicides… so you could have fewer sprays of conventional. Hopefully as products are developed we can do more and more of that,” he said.

What about potato beetles?

Bioinsecticides, however, may be facing an uphill climb against pests like Colorado potato beetle.

Common insecticides have shown less impact on the beetles in recent years. A three-year study near Winkler by Peak of the Market found that the window of neonicotinoid control was shorter, the Co-operator reported in 2018. Researchers in the study suggested that a longer spring emergence may make it more difficult to target control to the beetles’ life cycle, since multiple life stages will be present at the same time.

That may be an added challenge for anyone hoping that biopesticides might fill the gap.

“Most of the biopesticides tend to be a little more specific in terms of application timing, whereas the neonics were very nice in that timing was not critical,” Rossnagel said, although he added that most non-neonicotinoid insecticides, not just biopesticides, suffer from the shortened window.

Gevens says that challenge may be one reason that biofungicides could pull ahead when it comes to industry adoption.

Most biofungicides give a broader spectrum of protection than bioinsecticides, she said, assuming producers stay ahead of the infection.

“I think, in terms of the likelihood of adoption of these biopes­ticides for targeting the pest of disease, there’s perhaps greater success with disease management when you think about essential timing,” she said.

About the author

Reporter

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.

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