In late May, the Indiana Department of Natural Resources reported that an oak-killing fungus had potentially infested rhododendrons sold in Walmart and Rural King stores across the state.
Sudden Oak Death (SOD) fungus can travel on other plants without killing them. If host plants are then planted within six feet of an oak tree, the fungus can migrate to the healthy tree and kill it quickly.
Workers from the state Department of Natural Resources' Division of Entomology & Plant Pathology have been visiting stores across Indiana to destroy infested rhododendron stock. IDNR officials have destroyed thousands of rhododendrons and pulled thousands more from stores statewide. Any quarantined material not infected will be released following testing.
Locally, on May 29, Megan Abraham with the IDNR’s Division of Entomology and Plant Pathology confirmed that Logansport’s Walmart did receive shipments of rhododendrons from the nursery in Oklahoma where infested plants were shipped. Abraham also said that Logansport’s Rural King did not receive any of the plants suspected of carrying SOD.
“Any rhododendrons in [Logansport’s] Walmart have been pulled and destroyed” Abraham said at the time. “Other possible host plants that were too close to [the rhododendrons] have also been pulled for further testing.” Those tests are being performed at Purdue University. Four other common SOD host plants — viburnum, azalea, cameilia and pieris — have been pulled from the store while further testing is done to determine if they contain SOD.
Abraham said Monday that IDNR is "fairly certain" that the viburnum, azalea, cameilia and pieris plants pulled from Logansport's Walmart will be cleared of suspicion of SOD. "Some looked like they may have been infected," Abraham said, "but none have tested positive. So far, it appears that only the rhododendrons [which were destroyed] were infected." She said several hundred samples were pulled from the Logansport store and that only a handful of samples remain to be tested. However, the quarantine remains in effect until those last samples are cleared.
SOD has killed large tracts of oaks on the West Coast but has not been established in the Midwest. SOD can kill standing oak trees, which could happen if SOD-positive rhododendrons are planted within about six feet of a standing oak.
A BROADER THREAT
While Sudden Oak Death is immediate cause for alarm, it's far from the only threat to the state's native flora and fauna. Non-native invasive species can outperform and outgrow species that have traditionally lived in an area, often with dire consequences.
New legislation signed into law this year is designed to put a stop to the sale of 44 types of non-native plant species declared as pests or pathogens. Gov. Eric Holcomb signed the Terrestrial Invasive Species Rule on March 18, marking a series of most-harmful plants illegal to sell, offer or grow for sale, trade or distribution.
But the law doesn't go into effect until April 2020, allowing nurseries that were already cultivating the plant species a chance to unload their stock.
The legislation is designed to halt the march of invasive species and protect the state's wild lands.
Indiana landowners and managers spent over $5 million controlling invasive plants in 2012, according to a survey by the Indiana Invasive Species Council. The economic impact of invasive species globally has been estimated at 5% of GDP, which in Indiana approaches $15 billion.
The Indiana Native Plant Society lists a series of "Indiana's Bad Guys," or non-native plants that have been brought to the state, often as ornamentals for gardens or landscaping.
At the top of the list is Asian bush honeysuckle. Though beautiful to the eye with its brilliant red berries and green leaves, the species grows quickly and thickly, choking out large swaths of woodland.
Animals can suffer, too, if they rely on native plants for food.
The DNR shows that the honeysuckle, which was first planted to prevent erosion, has continued to infest new areas each year, spreading from the northeastern areas of the country to the west and south.
Asian bush honeysuckle is just one of dozens of non-native species DNR is warning residents to avoid.
Another is the popular Bradford ornamental pear tree.
"Over time, different varieties of pear have cross-pollinated in our urban areas, allowing them to rapidly spread into our natural resources," Abraham said.
Commonly available ornamental pear varieties include: Bradford, New Bradford, Cleveland select, autumn blaze, Aristocrat, capital and Chanticleer.
All of those should be avoided, DNR officials say.
Ridding an area of an invasive plant species takes a lot more than simply spraying a pesticide or clear-cutting the undesirable plant once or twice a year, said Kim Kaplan, chief of special projects with the agriculture research division of the U.S. Department off Agriculture.
"A landowner will have to inspect their land inch by inch several times throughout the growing season," Kaplan said. "And different species of plants can require different mitigation techniques."
The USDA and the DNR offer lists and guidelines on their websites for dealing with non-native plants, as well as guidance on native species that can replace invasives.
Meanwhile, Hoosiers are trying to battle established invasive species while keeping new ones, such as Sudden Oak Death fungus, out of the state.
If you have purchased rhododendrons recently, call 1-866-NO-EXOTIC (663-9684) or call the local county extension office at 1-888-EXT-INFO (1-888-398-4636) for instructions.
Kevin Burkett, editor of the Pharos-Tribune, contributed to this article.