Fighting pests with bigger pests: the Mother Nature method

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By J.W. Schnarr
Southern Alberta Newspapers — Lethbridge

Sometimes, you just have to let Mother Nature run its course.

In the case of zebra chip disease, lack of pesticide use by potato farmers may be helping keep the numbers of a tiny insect through which the disease is spread – a potato psyllid – is allowing natural predators of the creature to thrive in potato crops.

Professor Dan Johnson of the University of Lethbridge has been tracking psyllids in Canada for the past couple years and said while the tiny psyllids are here in very small numbers, so far there has been no evidence of zebra chip disease.

He recommended potato growers take no action at this time beyond field sampling.

Johnson co-ordinates the Canadian Potato Psyllid and Zebra Chip Monitoring Network, and leads the Alberta research project on the issue.

The psyllid has likely been present in Alberta in very low numbers for decades, but none of the insects found in Canada have tested positive for the bacteria that causes the zebra chip disease.

Johnson said the psyllids he has observed have been in good condition.

“It shows they live right up into Canada,” he said. “I think we have had a population that has never done very well up here. They are in very low numbers, but perfectly capable of acquiring and transmitting the pathogen.”

Zebra chip has caused millions in losses for potato farmers in New Zealand and the United States.

The psyllid, about the size of an aphid, feeds only on potato and tomato plants and some related wild plants, and can transmit bacteria that lead to zebra chip.

Infected plants are affected in growth, yield and quality. Potatoes with zebra chip, are edible but develop unsightly black lines that look like zebra stripes when fried. This makes them unsellable.

Since 2013, sticky yellow cards have been placed on stakes in some potato fields. Very small numbers were detected in 2015 and 2016.

“We’ve examined up to 2,000 cards a year at the U of L,” indicated Johnson in a news release.

“We didn’t want to be caught unaware,” he added. “The potato industry is very well-informed, and very science-based.”

Johnson said the amount of natural barriers present to stop the psyllids are a good example of ecological agriculture.

“If you manage the agriculture as though it’s an ecosystem that you want to work with instead of against, there are huge premiums from that way of doing things,” he said, citing sustainability and economics as incentives for ecological agriculture.

For gardeners, growers, and anyone else who would be interested in putting up a card, there is an opportunity to take part in the research simply by contacting Johnson.

He said it is a good way to learn more about the ecosystem in your garden or growing area, and it represents a unique opportunity for detecting psyllids.

“We’ll be happy to look at anybody’s card and tell them whether they have a lot of predators, or helpful (insects),” Johnson said. “We looked at a lot of gardens last year and didn’t find any (psyllids). If we find one, it’s really good news, because it adds a point to our map and we know how far this thing extends. It would really be helpful.”

“Gardeners should think of their gardens as a ‘sentinel site,’” he added. “If one is found in their garden, it doesn’t mean there is anything wrong. But they are the front guard for detecting this thing before some of the fields can detect it.”

“Gardens are on the front lines. It’s really valuable.”

Anyone interested in learning more about psyllids, zebra chip disease, or installing a card to help with with the project is asked to email Professor Dan Johnson at dan.johnson@uleth.ca.

There is also a newsletter available on the issue.

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