The remains of ash trees across northeast Indiana are sad reminders of the destruction caused by a beetle apparently introduced to the U.S. in wood cargo material nearly 20 years ago. Since 2004, the emerald ash borer has wiped out most of the area's beautiful ash trees. Now, the Indiana Department of Natural Resources is warning of an oak-killing fungal pathogen that has made its way to the state.
State officials have confirmed more than 70 Walmart stores and 18 Rural King stores in the state have received rhododendron plants infected with the pathogen, Sudden Oak Death. Shipments carrying infested plants were sent to nine other states as well.
Megan Abraham, with the state's Department of Entomology & Plant Pathology, said in an email that some of the plants were found in northeast Indiana.
“Division inspectors are visiting each store to pull and destroy infected material and inspect the rest of the materials there for signs of further infestation,” she wrote. “Many rhododendrons are sourced from out of state these days and it's not uncommon for these plants to have fungal diseases. P. ramorum, which is the fungus that causes Sudden Oak Death, is being surveyed for annually in Indiana and many other states.”
She advises anyone with concerns or questions to contact the DNR at 866 NO EXOTIC (866-663-9684).
Ricky Kemery, who writes “The Plant Medic” column for The Journal Gazette, said both rhododendrons and azaleas are susceptible to the disease. The Department of Natural Resources does inspect nurseries, he said, but “they are understaffed – this is probably the tip of the iceberg regarding this issue.”
Derek Veit, superintendent of forestry operations for the Fort Wayne Parks and Recreation Department, said the oak species and environmental conditions here are not the same as on the West Coast, so it's not known how local trees will be affected.
But the threat reinforces the city's decision to diversify its urban tree canopy after the ash borer infestation.
“Fort Wayne Parks and Recreation has been working toward a 10-20-30 species diversity goal,” Veit wrote. “The rule is a guideline intended to reduce the risk of catastrophic tree loss due to circumstances such as this pathogen. The guidelines suggests an urban tree population should include no more than 10% of any one species, 20% of any one genus or 30% of any family. It is aesthetically pleasing to plant similar tree species in defined spaces. This guideline is used as measuring stick to evaluate our urban canopy as a whole.”
As for the pathogen hosts, Kemery suggests rhododendrons and azaleas aren't good landscaping choices in this area anyway, based on soil conditions.
Avoid them and spare northeast Indiana the risk of more tree loss.