Oak-killing disease could be on its way to Minnesota, officials warn

The disease causes sudden oak death, and is feared to be making its way to the Midwest.
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DNR officials are asking Minnesotans to be on the lookout for a fungal disease that causes "sudden oak death."

Called Phytophthora ramorum, the invasive pathogen has killed in 30-45 million oak trees on the West Coast, mostly in the California and Oregon regions.

While no cases have been found in Minnesota, the Minnesota Department of Agriculture is asking residents to be on the lookout because it also affects around 100 plants, including rhododendrons.

The MDA says that rhododendrons infected with the pathogen has been found at several nurseries around the Midwest. Anyone who has bought a rhododendron in 2019 is being asked to inspect the plant for signs of infection.

Infected shrubs have leaves with "large, brown blotches," the MDA notes, with young green stems and shoots turning brown and shriveling.

"While rhododendrons may not die from this plant disease, our main concern is that the plants act as carriers of Phytophthora ramorum and could spread spores to Minnesota’s oaks," said MDA Plant Pathologist Michelle Grabowski in a press release. 

"Phytophthora ramorum has never been identified in Minnesota but it could have significant impact on the state’s forests and landscapes. Tests have shown that native trees like Northern red oak and white oak can be infected with Phytophthora ramorum."

Sudden oak death disease

Oak trees infected with the microorganism suffer a "bleeding" canker that turns the wood and bark reddish brown, with red liquid seeping out of the cracks.

It destroys the tissue that transports food and waters through the tree, killing the tree as it spreads.

Anyone with symptoms on a rhododendron should call or 1-888-545-6684 or email arrest.the.pest@state.mn.us.

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