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Deadly-to-plants pathogen identified in district
Cottonwood Extension District advises homeowners to examine new plants for signs
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These photos show leaf symptoms on infected rhododendrons. Symptoms can be confused with common problems such as sunscald. P. ramorum rarely causes death of nursery plants, but they serve as a source of infection for other nursery plants and to native oak plants. - photo by Courtesy

A new threat entered Kansas during the months of April and May. Slowing its spread now is going to depend a lot on collective vigilance and cooperation. 

Nothing like hitting the ground running. As the new Cottonwood Extension District Horticulture Agent Lauren Walz met for the first time and visited with Barton County Master Gardeners on Wednesday morning, she provided an important and timely education piece. 

On Tuesday, Walz saw firsthand a plant infected with the disease Phytophthora ramorum, also commonly referred to as Ramorum blight or Sudden Oak Death (SOD). The symptoms were discovered on a rhododendron belonging to an Ellis County client who had recently purchased the plant from a big box store in Hays. To Walz’s knowledge, it is the first confirmed case of the disease in the Hays area. 

A recent introduction to Kansas, the sighting comes on the heels of a release last week from the Kansas Department of Agriculture’s plant protection and weed control program confirming the presence of the disease in hundreds of rhododendrons sold at large retail stores in Kansas and 10 other states. All infected plants have been traced back to one source, according to the KDA press release.

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These photos show leaf symptoms on infected rhododendrons. Symptoms can be confused with common problems such as sunscald. P. ramorum rarely causes death of nursery plants, but they serve as a source of infection for other nursery plants and to native oak plants.
Plants removed from shelves

“The causal agent of SOD has been detected in rhododendrons originating from Park Hill Plants nursery in Oklahoma, and plants from that nursery were shipped to 60 Walmart stores across Kansas and one Home Depot store in Pittsburg, Kansas.” 

People who have purchased these or other landscape plants from these retailers in April and May should examine their plants carefully for symptoms that include foliar leaf spots, browning and wilting of leaves, and brown to black discoloration on stems and/or trunks. 

According to KDA, “Varieties that have been identified as infected include: Cat Cunningham Blush, Firestorm, Holden, Nova Zembla, Percy Wiseman, Roseum Elegans, and Wojnars Purple. Other varieties and other plant species may be infected as well. There are over 100 known species susceptible to P. ramorum, including, trees, shrubs and herbaceous plants. If you bought another plant from one of those locations and it is showing symptoms of SOD, it may be infected as well.”

The stores selling plants from the originating nursery have cooperated with KDA, USDA, and other states’ plant regulatory staff as they work to destroy all infected and potentially-infected rhododendrons still for sale, along with any other host plants in the vicinity. According to Walz, there is no treatment for the pathogen or disease and infected plants should be destroyed to prevent spread.

Potentially infected plants may not be labeled as Park Hill stock, Walz said. That’s because as an originating nursery, it is a wholesale supplier to a number of other branded nurseries. So, even if the plant purchased carries a label for a nursery other than Park Hill, if purchased between April and May this year from a big box retailer, it should be considered a potential host. 

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P. ramorum causes bleeding cankers on the trunk and a decline of the oak tree (Sudden Oak Death). Underneath the bark, the cankers have defined margins with a reddish-brown color as shown.
Local threat, disposal advised

Wednesday, Barton County Master Gardeners contacted management at the Great Bend Walmart to determine if the store was among the Kansas stores known to have carried the plants this spring. Management there stated last week, the entire stock of rhododendrons were recalled from stores including theirs and disposed of according to corporate protocol. 

Walz and Cottonwood Extension Ag Agent Alicia Boor met with the City of Great Bend. The city advises if you believe you have an infected plant purchased from Walmart in the last few months, burn them if at all possible. If prohibited, they recommend following the advice from K-State Extension: the plant should be removed from the landscape, double bagged and destroyed by throwing in the garbage. Sanitize any of garden tools and boots that may have come in contact with the suspect infected plant.

Stores where the plant was purchased should be contacted to discuss a refund.

While the disease rarely kills foliar hosts, the disease is deadly when it infects oaks, as its name implies. According to the Kansas Forest Service, “while most native oaks like bur oak are of the potentially less-susceptible white oak group, there are millions of red, black, pin, shumard, blackjack, shingle, and other oaks that could be impacted should this disease gain a foothold in the state. 

“When it infects oak trees, there’s no known cure and it can kill a tree very fast,” Walz said. “Normally, it wouldn’t have a chance to get going in western Kansas, but this year, with all this rain, it’s another story.” 

That’s why it is important to halt introduction of any suspected plants now and to remove any potentially infected material from the landscape before the disease can get a foothold, Walz said. Barton County Master Gardeners will have an educational display set up at the Barton County Fair next month with information about the disease. 

According to a June 7 special alert from K-State Extension, the presence of the disease is a serious situation. "SOD is a plant disease that has killed large tracts of oaks and other native species in California and Oregon. It also occurs on nursery plants including rhododendron, azalea, camellia, viburnum, lilac, and periwinkle." 

And, since it is a relatively new disease, future research may identify other plants it occurs in.