Wisconsin oaks at risk due to potential for disease in rhododendrons, azaleas

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(WFRV) — If you bought rhododendrons or azaleas this spring and summer, state plant health officials warn to be on the lookout for signs of a disease that could spread to oaks and kill them.

Plant health staff with the Department of Agriculture, Trade and Consumer Protection have identified Phytophthora ramorum, or P. ramorum, on rhododendrons at a northern Wisconsin nursery.

Officials say the fungus causes sudden oak death, which has never been found on the landscape in Wisconsin.

There is no human health risk according to DATCP.

The find resulted from a July survey of 59 garden centers and nurseries in the state after it was reported that potentially infected shipments originating from a Washington state supplier had gone to these businesses.

Wisconsin inspectors collected 43 samples, but only one was found positive for the fungus.

Officials says consumers should look for leaf and shoot dieback as potential symptoms.

Plants suspected to be infected should be sent to the University of Wisconsin-Madison Plant Disease Diagnostic Clinic. There is no cost for this.

For more on how to submit a sample, click here.

Officials say they do believe many of the distributed plants are negative for the fungus, but there is still some concern due to a positive test being found.

Susceptible plants at the supplier and the nursery are being destroyed and owners are disinfecting soil and equipment.

While the fungus may not kill rhododendrons and azaleas, it can be transmitted to as many as 100 different plant species, including hardwoods, softwoods, and shrubs.

Oaks are reportedly at the greatest risk because of P. ramorum being incurable. It has killed 30-45 million oaks in California and Oregon.

Spores from the disease can travel in plants, soil, gravel, potting mixes, wind-blown rain, and other water sources.

Contaminated pots, shovels, and other equipment could also transmit the disease if not sterilized with bleach.

For more information about sudden oak death, click here.

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