Problematic bacteria thrives after copper applications

By MITCH LIES

Capital Press

PORTLAND -- An Oregon State University plant pathologist is recommending growers stop using copper for bacterial canker control in cherries.

"Let's not use copper," OSU plant pathologist Jay Pscheidt said Jan. 25 at the Northwest Ag Expo. "I think it's been causing more problems than it has been helping."

Pscheidt said copper-resistant Pseudomonas syringae, the bacteria that causes the canker, has been found in several orchards in recent years. Research, in fact, has indicated copper use is leading to increased disease pressure.

"Rather than getting no control, we're seeing worse disease," Pscheidt said. "That's why we're recommending to not use it in cherries."

Bacterial canker can lower yield and fruit quality in cherries and other orchard crops. It is especially harmful to young trees.

Pscheidt offered several keys to minimize impacts from the canker, including:

* Avoid planting trees in frost pockets where poor drainage can induce tree stress.

* Get soil tested and use lime if needed to alter its acid profile.

* Treat with a fumigant if nematode populations are high.

* Delay pruning until late in the dormant season.

* Remove infected cankers.

Pscheidt also warned growers to watch for plant diseases this year.

Heavy disease pressure last year was triggered by a wet spring. That means a lot of pathogens are overwintering, he said.

"If the weather is favorable for disease this year, we could have another heavy disease year," he said.

"Do extra scouting," he said. "If something unusual pops up, have it diagnosed so you know what you're dealing with."

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