Monitoring stepped up, insecticide treatments planned

By JOHN O'CONNELL

Capital Press

Idaho researchers have released details of a state management plan intended to minimize damage caused by zebra chip, a potato disease that first arrived last season in the Pacific Northwest.

Zebra chip, caused by the bacterium Candidatus liberibacter solanacearum and transmitted by potato psyllids, was first detected in Oregon, Washington and Idaho last fall. It causes bands of necrotic flecking in the flesh of potatoes, resulting in extreme darkening when fried.

The University of Idaho will implement a potato psyllid monitoring plan, funded by the Idaho Potato Commission, which entails intensive studying of at least 11 fields around the state to learn more about best management practices and the spread of the disease.

Most of the fields will be in areas hardest hit by zebra chip, but some in Eastern Idaho, which wasn't badly impacted, will also be monitored. Growers can register to receive notifications at www.pnwpestalert.net or can check updates at MillerResearch.com or kimberly.uidaho.edu/potatoes.htm .

It's recommended that growers scout for psyllids around May 15 and no later than June 1, depending on crop growth stage. Photographs of psyllid life stages are available at potatoes.com/research.cfm .

Yellow sticky cards used for trapping adults should be placed on the edges of fields and should be checked and replaced at least on a weekly basis. Leaves should be sampled for eggs, nymphs and adults. The suggested strategy is taking 10 leaves, focusing on the middle of the potato plant, from 10 different locations within 30 feet of the edge of the field.

Furthermore, growers may wish to take 100 sweeps into their fields from the edges, catching insects that fall from plants using nets. Insects should be frozen and saved for analysis.

Officials will map where psyllids are detected in Washington, Oregon and Idaho, and whether they're infected with the bacterium that causes zebra chip.

In the Magic and Treasure valleys, where zebra chip was most problematic in Idaho, officials recommend treating at planting with a neonicotinoid insecticide and following up with a foliar insecticide when the initial treatment loses effectiveness.

Foliar recommendations are available at potatoes.com/pdfs/PotatoPsyllid.pdf. Farmers should avoid foliar neonicotinoid applications if that class was used at planting to prevent insecticide resistance. Also, they should avoid pyrethroid insecticides for controlling psyllids, as they may flare populations by enticing females to lay eggs.

In areas of Idaho where zebra chip wasn't a problem in 2011, officials recommend following traditional insecticide programs but considering a neonicotinoid insecticide application at planting. If updates reveal a threat by psyllids, they should follow with a foliar program.

The University of Idaho will host periodic training sessions throughout the state on psyllid identification.

"We want to empower our industry because if this is something that's going to be around for a long time, we want to get a good education program and training program," UI Extension potato specialist Nora Olsen said.

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