Insect found in Alberta but disease not present

The psyllid story sets up like a good news-bad news scenario.

The bad news is that the potato psyllid, a tiny insect that can carry zebra chip disease that is harmful to potato production and appearance, has been found in Alberta.

The good news is that it isn’t carrying the disease.

Dan Johnson, an entomologist and researcher at the University of Lethbridge, is the lead on a national project to monitor for the presence of the potato psyllid. Field surveillance has been underway since 2013.

The first potato psyllids were identified at the end of July in small numbers, said Johnson, and subsequent testing showed they are not carrying the pathogen for zebra chip.

“As of Aug. 13, a total of nine potato psyllids have been collected on yellow cards in Alberta during the last two weeks, and we expect more,” Johnson wrote in a report.

“The rate of collection on cards that I monitored was six psyllids on about 24 cards, with additional ‘zero’ cards in the surrounding area. This is a low population.

“At this time, there is no evidence of zebra chip pathogen in insects, disease symptoms or infection of plant tissue in Canada.”

Zebra chip can devastate potato crops, causing black stripes in the tubers and making them unsuitable for consumption. It also affects production, causing stunting and leaf cupping.

Potato crops in Idaho, Oregon and Washington have been lost when the potato psyllid is established and carries the disease.

Terence Hochstein, executive director of Potato Growers of Alberta, said this isn’t the first time potato psyllids have been found in Canada, but zebra chip hasn’t been found with them.

He said the monitoring network project is doing its job.

“The positive side about all of this is it allows the industry, it allows the growers, it allows Canada, to have all their ducks in a row if the worst happened,” said Hochstein.

“Washington and Idaho didn’t have that luxury. They found out about it after the crop was infected a couple years ago.”

Psyllids are one to two millimetres long, the approximate size of aphids, and resemble tiny cicadas. They can travel on the wind, plant material and vehicles.

The surveillance project involves placing yellow sticky cards in potato fields and environs. The cards are collected one week after placement, and Johnson analyzes the insects that have been trapped.

With samples coming in from across Canada, it will take some time to determine whether there are potato psyllids elsewhere in the country. None were found in 2013 or 2014.

Johnson said all potato psyllids identified so far have been adults, and he doubts they flew in from elsewhere because their wings didn’t show the wear normally associated with long distance flight.

“Although long distance flight and movement on upper air is possible, I suspect that these potato psyllids come from a small local population that may have moved in several steps, established itself undetected until now and then produced a generation which dispersed out a short distance.”

Johnson said the sticky cards have also found many natural enemies to psyllids, which is good news for future control.

“It is possible that natural suppression will (be) a factor in holding numbers down,” he said.

“The low use of insecticides by growers appears to be returning very important benefits for integrated pest management.”

The surveillance and monitoring program is funded by the Canadian Horticultural Council and Growing Forward 2 and involves participants from municipal, provincial and federal government departments and academia.


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