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ST. LOUIS — A plant pathogen that causes an invasive tree-killing disease has been found in both Missouri and Illinois.

The Missouri Department of Agriculture says it has detected ramorum blight on rhododendron plants shipped to some retail nurseries in Missouri.

The disease is more commonly known as Sudden Oak Death when it infects oak trees.

The rhododendrons were shipped to Walmart and Rural King stores throughout Missouri, as well as the Springfield Home Depot, Stark Bros. Nursery Garden Center and Fort Leonard Wood PX.

The Illinois Department of Agriculture last week confirmed it found the pathogen at 10 Walmart stores and one Hy-Vee.

Agriculture officials urge consumers who purchased rhododendrons or lilac plants of the known infected varieties labeled Park Hill Plants from these stores between March and June of this year should dispose of the plants immediately. There is no treatment for the pathogen.  

If you’re unsure of the plant's variety, look for wilting or browning leaves, leaf spots and twig dieback. If you spot those symptoms in Missouri, contact the Agriculture Department’s Plant Pest Control team at (573) 751-5505 and begin the disposal process.

Sudden Oak Death caused by a fungus-like pathogen known as Phytophthora ramorum. Since the 1990s, the plant disease has caused mortality in some types of oak trees in California and Oregon, but it has not established itself in the Midwest.

Shipment of these rhododendrons has been successfully traced back to Park Hill Plants in Oklahoma and may have originated from nurseries in Washington State and Canada. Plant varieties identified during the investigation, which is still partially ongoing, were shipped to at least 18 states.

In addition to Missouri, other Midwestern states where the pathogen was detected are Iowa, Illinois, Indiana, Kansas and Nebraska.

The issue first emerged with rhododendrons at an Indiana Walmart in late May.

Specific varieties of rhododendrons that have tested positive in destination states include Cat Cunningham Blush; Firestorm; Holden; Nova Zembla; Percy Wiseman; Roseum Elegans and Wojnars Purple. Specific varieties of lilac that have tested positive in destination states include: Common Purple and Persian Lime.

Sudden oak death poses no threats to humans, animals or food sources, experts say.

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