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Psyllids and Zebra Chip

University of Lethbridge biogeography professor Dan Johnson has been monitoring Prairie potato fields for the past few years, looking for evidence of the potato psyllid and a bacterium it can carry that can lead to zebra chip disease in potato crops.

The good news: So far in 2017, the number of potato psyllids has been lower than in previous years, both in Canada and the U.S.

The better news: None of the potato psyllids or potato plant samples tested were carrying the bacterium that causes zebra chip — Candidatus Liberibacter solanacearum (Lso).

During the 2017 crop year, Johnson – who coordinates the Canadian Potato Psyllid and Zebra Chip Monitoring Network – and his team monitored 40 potato fields to the potato psyllid. By mid-August, total psyllids caught on “sticky cards” numbered 45.

The number isn’t unexpected: the team located the potato psyllid in Alberta at numerous locations in 2015 and again last year, and in Manitoba and Saskatchewan in 2016. This year, sticky cards were set out again in Alberta, Saskatchewan and Manitoba, as well as in Ontario, Quebec, New Brunswick and British Columbia.

Zebra chip is caused by a pathogen, Candidatus Liberibacter solanacearum (Lso), transmitted during feeding by the potato psyllid, but not by other insects. Plant growth, yield and quality are strongly affected, and the striped appearance of affected tubers reduces value for processing. Other symptoms of the infected plant include leaf deformity, chlorosis, bud proliferation, and yellow or purple discoloration. The disease can result in loss of crops and infection of stored tubers.

The Canadian Zebra Chip and Potato Psyllid Survey and Monitoring program began in 2013 in cooperation with Scott Meers, insect management specialist with Alberta Agriculture and Forestry. Larry Kawchuk, research scientist with Agriculture and Agri-Food Canada in Lethbridge, conducts testing of the psyllids and plants for the Lso pathogen. Johnson’s team also includes a network of researchers and collaborators who participate in conducting field sampling, identifying species and stages, mapping occurrence if found, developing and implementing a monitoring program, assessing the effects of weather and regional variations and movements, determining potential geographic range, constructing a geographic forecasting model of the insect life history and development, and developing a management plan.

While populations of the tiny insect remain relatively low, Johnson remains vigilant about ensuring zebra chip does not enter Canada. For while the zebra chip pathogen has not been detected here, it’s a different story elsewhere – zebra chip was first discovered in Mexico in 1994 and in Texas in 2000. Since then it has spread through much of the western half of the U.S., into several Central American countries and New Zealand.

Zebra chip presents a potential high economic risk to potato production. Estimates in other regions indicate severe impacts. For example, it is estimated that Eastern Idaho would suffer a 55 per cent reduction in returns for potato producers, and an inability of Pacific Northwest growers to sustain a profit if they adopt a routine insecticide program for zebra chip protection that begins at plant emergence. Annual losses in Texas have been reported in the range of US$25 to US$30 million.

Back in Canada, Johnson and his team continue with their work, surveying fields for populations of the potato psyllid in Canada, and testing captured psyllids and symptomatic tubers for the presence of the disease agent.

While psyllids are likely here to stay, we can only hope the zebra chip pathogen stays out of Canadian potato fields indefinitely.

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