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MDC Offers Advice After Sudden Oak Death Introduced Into Missouri On Nursery Plants


A few weeks after the U.S. Department of Agriculture announced that an invasive pathogen had been introduced into Missouri on nursery stock, the Missouri Department of Conservation and other organizations are being extra vigilant.

The pathogen, Phythophthora ramorum, was brought in on rhododendron and lilac plants from Washington and Canada that were sold at retail outlets, including Walmart stores throughout Missouri, Home Depot in Springfield, Stark Bros. Nursery Garden and Fort Leonard Wood PX.

Natalie Diesel, forest pathologist for MDC, said the pathogen can cause ramorum blight, which infects the leaves and stems of certain plants but doesn’t necessarily kill them.  But it can also cause sudden oak death, “the relatively rapid death of these trees caused by trunk cankers,” she said.

More than a million oaks and tanoaks have been killed by Phythophthora ramorum in California and Oregon since the 1990s, and the disease continues to spread there.  It appears mainly to affect members of the red oak family, according to Diesel.  And, in Missouri, there's plenty of forests with those kinds of trees.

“What we don’t know is if our climate is suitable, if, in some areas, we have the necessary foliar hosts that are necessary to kind of perpetuate the disease in the environment,” she said.

Foliar hosts are things like rhododendrons where the pathogen causes leaf spots or small branch dieback.  Phythophthora ramorum is able to complete its life cycle on those hosts and produce spores, which allow it to reproduce.  Those hosts are necessary for the pathogen to exist in an area.  And there are more than 100 known plant hosts, according to Diesel.

“I would expect that in just about anywhere in Missouri we have foliar hosts present,” she said.

Oaks are a sort of “dead end” for the pathogen, according to Diesel.  The trees can die from an infection, but the pathogen isn’t able to produce spores on them. 

“We’re certainly concerned that Phythophthora ramorum has been introduced,” she said.  “We don’t want to cause panic because we don’t know if this is going to potentially infect and kill oak trees or if it will persist in Missouri.”

Anyone who bought rhododendrons or lilac plants labeled “Park Hill Plants” between March and June should watch for signs of the disease:  Leaf spots that are brown and spreading, possibly following leaf veins, and twig dieback.

If you suspect you might have a diseased plant, you should follow the U.S.D.A.’s recommendation for removal.

Those include burning the plants or double bagging them, including their root system, in heavy duty trash bags for disposal at a landfill.  Don’t mulch or compost them or take them to a yardwaste facility.

You should also monitor your oak trees.  Signs of infection include stem cankers—areas of stained, dark tissue on oak tree trunks that are oozing dark brown, reddish or black sap.

But Diesel said, while you should be vigilant, don’t immediately assume the worst if you notice canker sores on your oak trees.

“There are many, many causes for that, whether it’s native borers getting into the tree or some damage that’s occurred and there’s some fungi—some native fungi potentially in there acting,” she said.

But she said you should check with your local MDC forester to make sure the tree isn’t infected with Phythophthora ramorum.

Diesel said MDC is working closely with the Missouri Department of Agriculture and the U.S.D.A. and will also work with local foresters to investigate any reports of sudden oak death on trees.

Michele Skalicky has worked at KSMU since the station occupied the old white house at National and Grand. She enjoys working on both the announcing side and in news and has been the recipient of statewide and national awards for news reporting. She likes to tell stories that make a difference. Michele enjoys outdoor activities, including hiking, camping and leisurely kayaking.