Published online: Jul 30, 2012 Insecticide, Fungicide
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While other potato growers use preventative insecticide applications to protect their crops from a new disease to the Pacific Northwest called zebra chip, Fred Brossy can only wait and see if it hits him.

Brossy grows organic Yukon golds in Shoshone, Idaho. He's becoming increasingly concerned about zebra chip-caused by the Liberibacter bacteria and spread by tiny aphid-like insects called potato psyllids-as researchers continue to find infected psyllids and potato plants in Idaho.

"I don't know of any organic option for potato psyllids at this point," Brossy said, adding that even if there were a treatment option for organic producers, it wouldn't be labeled yet.

Zebra chip reduces yields and makes spuds unmarketable, leaving bands in tuber flesh that darken when fried. Brossy is hopeful the damage caused last season-the first arrival of zebra chip in the Pacific Northwest-will prove to be an anomaly. But he also acknowledges "if it continues to spread then what are we going to do? It could be a real deal breaker for us."

Erik Wenninger, an entomologist at the University of Idaho's Kimberly Research and Extension Center, said trials are under way at his facility to determine if bacterial-based Spinosad insecticides, which are among the few options available to organic producers, are effective against zebra chip. However, he has no advice for organic growers for the time being.

Organic growers can only wait and hope.

"Absolutely I'm concerned (about zebra chip) because there isn't anything I can do about it," Mike Heath, an organic potato farmer in Buhl, Idaho, said.

Heath said Colorado potato beetle is the only insect that currently bothers his crops, though he didn't need to treat for the pest this season. He believes improved biological activity and beneficial insects in organic fields could provide protection from psyllids.

"A lot of problems conventional growers have in a lot of their crops never are big problems for us. I'm hoping that's the case for (zebra chip)," Heath said.

According to an alert emailed to growers, three symptomatic plants recently found at the Kimberly center have tested positive for Liberibacter, and other symptomatic plants found at the facility are being tested. Several plants found July 17 in a grower's field were also confirmed positive for Liberibacter. Furthermore, infected psyllids have been found in Twin Falls County, and psyllids found in two Canyon County potato fields are now being tested for the bacteria.

Wenninger said psyllid populations have been much higher in Oregon and Washington. However, infected psyllids and potato plants have not yet been found outside Idaho in the Pacific Northwest.

Wenninger explained psyllid survival is adversely affected by Liberibacter, which could explain why Idaho's psyllid counts have been lower despite the fact that it has had zebra chip cases this season.

"It's probably not safe to assume they don't have any psyllids with the bacteria in Oregon and Washington. They just haven't found any yet," Wenninger added.

SOURCE: John O'Connell, Capital Press