Zebra chip pathogen makes debut in Alberta potato fields

The zebra chip pathogen that can cause a serious disease in potatoes has been found for the first time in southern Alberta.


Carried by an insect called the potato psyllid, the pathogen called Liberibacter solanacearum (Lso) causes dark stripes in potato tubers and makes them unsellable and unsuitable for processing and consumption.


The good news is that very few potato psyllids have been found in Alberta and of those, few have been found to carry the pathogen. 


“Almost always (the tests) come back negative, but this latest news is that a couple weeks ago they started coming back positive. We’ve had at least eight and I think we’re up to about 12 cases where they’ve been positive for the bacterium.”


No potatoes with the virus have yet been found and monitoring of insects and stored tubers is ongoing.


“The Lso bacteria is here in the bug and if that also gets into a plant, it can cause zebra chip, but there’s been no zebra chip in Canada yet,” said Dan Johnson, co-ordinator of the Canadian Potato Psyllid and Zebra Chip Monitoring Network.


“It might seem like bad news to people that we turned it up, but it’s only because we’re looking so hard. And I’m emphasizing that it is at very low levels.”


Discovery of the threat at this early stage gives growers time to develop a strategy, said Johnson. 


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“Working in our favour here, this particular insect has never been very common. It’s always been at very, very low numbers.”


Zebra chip has infected potato crops in Mexico, Texas, Oregon, Washington and Idaho, where it has caused millions of dollars in losses.


The monitoring program began in 2013. In the first year, about 10 potato psyllids were found, none of them carrying the pathogen.


Then they found 50 or 60, and the year after that about 150 or 200.


“That’s not very many insects, considering how hard we were looking,” said Johnson, noting the network was monitoring 42 sites across the province by placing four cards at each site and collecting them every week.


“I estimated one day that we’ve looked at a couple million insects. And if you only find 200 potato psyllids, that shows you how rare they are compared to other insects that are out there.”


The DNA testing of the psyllids and identification of any pathogen they carry falls to Agriculture Canada research scientist and insect pathologist Larry Kawchuk.


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Although the pathogen-carrying insects have been found, there is no sign of the disease in potatoes themselves.


“We are very sure we are zebra chip free,” Kawchuk said Oct. 23. “If we take the right steps, we could probably remain zebra chip free. We’ve advised the industry to set up and establish a monitoring program with the processors and the producers.”


Besides tests on insects, Kawchuk said he and others in his lab have been testing plant tissue and will continue that at least until current funding for the project runs out.


To date it has been funded by the PGA and by Growing Forward 2 through the Canadian Horticultural Council. 


Johnson described the psyllid and zebra chip watch as “a needle in a haystack. In fact, it was like a particularly small needle in a particularly large haystack.


“Part of the good news is that we know right where it is and we know where it isn’t and we found out way in advance of what we would need for last minute management. 


Potato psyllids have many natural insect enemies and although there are insecticides that can kill psyllids if they become a major problem, Johnson advised caution in favour of biological solutions.


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