Staff Reports
The Indiana Department of Natural Resources has confirmed more than 70 Walmart stores and 18 Rural King stores in Indiana received rhododendron plants infected with a pathogen that kills oak trees.
Some of the plants were found in Columbus over the Memorial Day weekend, according to the DNR, with others located in Noblesville, South Bend, and Sullivan and Tippecanoe counties.
Workers from the state’s Department of Entomology and Plant Pathology are visiting stores across Indiana to destroy any stock that is determined to be infested with the pathogen and to quarantine any stock that is symptomatic, the DNR said.
Megan Abraham, Division of Entomology and Plant Pathology, said Columbus’ Walmarts and Rural King are among those believed to have had the rhododendrons that are being confiscated and destroyed.
The DNR has destroyed about 1,500 infested rhododendron across the state so far, and pulled another 1,500 plants of other types from stores, the DNR said Wednesday. Any quarantined material not infected will be released following testing at Purdue University.
DNR officials are also following up with homeowners who have notified state officials that they have purchased plants that could be infested or are seeing signs of a sick tree.
The fungal pathogen that kills oak trees through sudden oak death (SOD) has killed large tracts of oaks on the west coast, according to the DNR. While the pathogen has not been established in the Midwest to date, the DNR is warning that any pathogen-positive rhododendron plants that are placed within 6 feet of a standing oak could kill the tree.
The pathogen can travel in more than a hundred species of host plant material. It causes some browning of the leaves in the host plant but does not kill it.
The Indiana Department of Natural Resources is destroying all rhododendrons from the source nursery, Park Hill Plants (Oklahoma), and any other host plants that were co-mingled with them.
In addition, the department is quarantining the sale of four other common pathogen-host plants (viburnum, azalea, cameilia, and pieris) for further testing to determine if they are positive for SOD.
Testing will determine if other species are infested and require destruction, the department said.
The DNR is advising that if you have purchased rhododendrons in the last four weeks from Walmart or Rural King, you should destroy them, or call the local county extension office at 1-888-EXT-INFO (1-888) 398-4636 for instructions.
Boxwood blight
In a related notice, the DNR is also warning consumers that a shipment of boxwood plants at Home Depot stores contained the boxwood blight fungus.
The DNR said the shipment originated from a nursery named Cottage Gardens in Ohio.
Boxwood blight (Calonectria pseudonaviculata) is a fungal disease that infests members of the popular Buxaceae family, and is often transported through the nursery trade. Hosts include Buxus (boxwood), Pachysandra (Japanese spurge) and Sarcococca (sweetbox).
Annual inspections of nursery stock by the DNR verify that this pathogen is not indigenous to Indiana, nor can it be found in nursery stock that is sourced locally.
When the fungus, which can remain dormant in drier conditions, is present, it can be found on all above-ground portions of the plant and presents itself as dark leaf spots. It causes rapid defoliation, which typically starts on the bottom of the plant and moves toward the top. This fungal pathogen can move through sporulation in water and from dropped leaves. As a result, infection can spread to surrounding plants from a single infected plant.
The infected nursery stock is being pulled from shelves in 13 Home Depot stores by nursery inspectors and Cottage Garden representatives, and will be disposed of in a manner that will prevent the pathogen from spreading to other stock.
There are several varieties of boxwood sold in Home Depot stores. The only species that is currently testing positive for the fungus is Korean boxwood (Buxus Koreana), however the DNR is testing other species to ensure the pathogen has not spread.
If you have purchased a Korean boxwood from a Home Depot store in the last month, contact the DNR for further guidance at 866-NO EXOTIC.
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For a list of plants that can carry the sudden oak death pathogen, visit aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/pdf_files/usdaprlist.pdf.
Anyone who has purchased rhododendrons in the last four weeks in Columbus, or the other communities, is asked to call 866-NO-EXOTIC (663-9684) or call the local county extension office at 1-888-EXT-INFO (1-888-398-4636) for instructions. The DNR is advising customers who may have purchased the rhododendron plants to destroy them immediately.
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