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Published June 11, 2012, 08:00 AM

Gudmestad educates about zebra complex

EDINBURGH, Scotland — Neil Gudmestad tells audiences he’d like to change the name of “zebra chip,” disease to “zebra complex.” But it seems the powers of an international potato disease expert have their limits.

By: Mikkel Pates, Agweek

EDINBURGH, Scotland — Neil Gudmestad tells audiences he’d like to change the name of “zebra chip,” disease to “zebra complex.” But it seems the powers of an international potato disease expert have their limits.

Gudmestad, a plant pathologist with North Dakota State University in Fargo, was one of the featured speakers at the 8th World Potato Congress in Edinburgh, Scotland. It’s his third time speaking at the event, which is held every three years somewhere in the world.

Gudmestad spoke twice to groups of world experts, offering insights into the disease causes streaking in potatoes. There are limited insecticide options against the tomato/potato psyllids — insects that carry the disease bacteria — which stunts plant growth sometimes cutting yield and ruining quality for market, with streaking.

Growers in south Texas, for example, have delayed planting three to four weeks to avoid the bacteria in the psyllids. Some plant potatoes like cotton — planting the outer edges, into the center fields. “If they’re planted in a circle, they can also be harvested in a circle, around the circumference of that field,” he explained. The potatoes with higher infestation can be blended in when they go to market, so they can be below economic thresholds.

Fortunately, the disease hasn’t made it to North Dakota — yet.

Psyllids moved into the state in July 2010, but tested negative for the disease. The bacteria live in the phloem of the plants, the material that carries nutrients from the leaves to the roots to the potatoes. The disease was first seen in Mexico in the 1990s and moved into the U.S. in 2000.

“The population built up really quickly in Texas in 2012,” Gudmestad said. Because of the early spring, the insects became mobile four to six weeks earlier, and already got to Nebraska where it has built up a population on cull piles of potatoes that never made it to market.

“We still have a big concern that the psyllid at least can get to North Dakota very early this year,” he said. Processors and producers, as well as the Northern Plains Potato Growers Association and Area 2 Minnesota growers, those outside the Red River Valley, for the first time have put in place a pre-season trapping network in the region for the 2012 crop.

A new defense system recently has been put in place for the north central states. “Six sites in North Dakota and six sites in Minnesota, and those are all negative so far for the psyllid,” Gudmestad said.

Yellow sticky cards, about 4 by 6 inches, are attached to a piece of lath that are stuck into the ground. Before the crop is up, the pre-season line is along some fence line or tree line where there is green material that would attract the psyllids as they fly in. The insects are attracted to yellow.

“Once the crop is up, as it is now, that trap line moves to peripheral areas around fields. The crew places a trap every 150 feet in toward the center of the field. Those are removed weekly and sent to Texas for analysis. Along with that, five leaves in the area of the sticky trap are sent in and analyzed for psyllid eggs and nymphs,” Gudmestad said.

He said the R.D. Offutt company has been a big contributor to the Specialty Crop Research Initiative ZC project from the beginning. “They’re really heading up this project,” Gudmestad said. RDO and Lamb-Weston in Minnesota have been contributors to the overall project, and requested the project undertake the defense system.

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