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Investigation of Pest Under Way in Idaho

In early May, officials from the Idaho State Department of Agriculture (ISDA) and the Animal and Plant Health Inspection Service (APHIS) were still trying to track down the source of two tiny cysts – the size of pinheads ¬– that have halted exports of fresh Idaho potatoes to three countries.

Reports in late April said the field source of the potato cyst nematode cysts had been identified, but these reports were not accurate, said Wayne Hoffman, special assistant to the director of the ISDA. That still remained a mystery.

The two cysts were found in tare dirt at a processing plant in eastern Idaho during routine monitoring that takes place under the Cooperative Agricultural Pest Survey (CAPS). That program, in Idaho and all other potato-producing states, conducts routine surveillance inspections for nematodes and some 400 other pests.

The source of the tare soil was thought to be two 500-acre fields in eastern Idaho, where intensive sampling began. The two cysts were found in the processing plant, their identities were confirmed as Globodera pallida (the white, or pale, cyst nematode) and the finding was announced on April 19, Hoffman said. By May 3, a dozen workers had collected 1,682 soil samples from the fields and sent them the nematology laboratory at the University of Idaho. But no cysts had yet been found in any field samples, he said.

The University of Idaho laboratory said it would take about two weeks to analyze the samples.

APHIS and ISDA are also working to trace the origin of the seed that was planted in the fields.

In accordance with international guidelines, APHIS informed trading partners and the North American Plant Protection Organization about the detection. Within days, Canada, and then Mexico and Japan, closed their doors to shipments of fresh potatoes from Idaho.

Canada called its ban temporary, but it is not known how long any of the shipping bans will last.

Japan’s ban extended to all United States fresh potatoes, a sudden stop to a short relationship. Fresh market potato exports to Japan only just began in February; that market had been closed to U.S. fresh potatoes for decades.

The nematode does not pose any threat to human health, but can devastate yields of potatoes and other solanaceous crops, including eggplant and tomatoes.

APHIS issued an Emergency Action Notice restricting the movement of soil and potatoes from some Idaho facilities, including the processing facility where the sample was collected.

“This step was taken as a precaution until the facilities can be thoroughly evaluated and we can confirm that they pose no risk of spreading potato cyst nematode,” an APHIS spokesman said.

Processed potatoes are not considered a source for infection because nematodes cannot survive the cooking process, which includes steaming and drying. They can move on fresh tubers.

John Keeling, executive vice president of the National Potato Council, said the implications for resuming trade are good.

“Once you get the extent of the find delimited and get your management mechanisms in place, you can start talking about resuming trade,” he said. “Once you gain official control, you can start the dialogue with your trading partners.”

The restrictions now are broad. But once the tracebacks are complete and the extent of the problem is known, Keeling said the restrictions will likely narrow to a field or an area ¬– not an entire state or country.

“That’s what done in New York with the golden nematode,” he said.

He noted the situation with Japan as “very unfortunate. We worked for 29 years to open the market and it closed after two months.”

The potato cyst nematode is a major pest of potato crops in cool temperate areas. It primarily affects plants within the potato family including tomatoes, eggplants and some weeds. If left uncontrolled, nematodes can cause up to 80 percent yield loss.

There are two species of the nematode, the golden or yellow and the pale or white, the two differing in the color of the cysts. Cysts are in fact the bodies of dead females that contain from 200 to 600 eggs each. These eggs, according to scientific literature, hatch when certain chemicals are exuded by roots of potatoes, tomatoes, eggplant and nightshade plants, signaling that a host is present and it’s time to hatch and feed. Cysts may remain dormant 20 years or more waiting for a suitable host.

The potato cyst nematode is widely distributed in many potato-growing regions throughout the world, according to APHIS. In North America, the golden nematode is known to be present in Newfoundland and Long Island, New York. Originating in South America, potato cyst nematodes appeared in Europe in the 1880s and are in Europe, Australia and elsewhere.

Potato cyst nematode infestations may be associated with patches of poor growth. Affected potato plants may exhibit yellowing, wilting or death of foliage – none of which has been observed in Idaho potato fields.

PCN life cycles are tuned to a single crop, according to scientific literature. They hatch, feed on potato roots, mature and die by flowering time. They infect roots, not tubers.

When the nematode becomes established in a growing area, producers have to adopt measures to reduce damage, Hoffman said. These include equipment sanitation, crop rotation, nematicides (fumigants or granular systemic compounds) and the use of resistant potato cultivars. The common rotation recommendation is seven to 10 years without potatoes or related crops. The integration of these methods can be used to keep the nematode population levels below economic thresholds.

Meanwhile, Hoffman said, “It’s very early at this point. Be patient.”

Two dozen inspectors were combing fields, taking samples, looking for clues that would determine the size and significance of the findings. Right now, that’s two cysts in a pile of dirt.

Originally posted Saturday, Apr. 7, 2007

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