The Hoosier Gardener: Deadly boxwood blight found in Indiana

Jo Ellen Meyers Sharp

IndyStar correspondent

Boxwood blight turns the leaves brown and darkens the stems on the shrubs.

A dreaded, fast-killing fungus disease was discovered on boxwoods earlier this month in at least one big-box retailer in Indiana.

Boxwood blight starts out as rounded dark brown spots on the leaves. The evergreen shrub then quickly loses all of its leaves.

The shrubs were shipped from Oregon to 23 stores in Indiana in May, according to a news release from the Indiana Department of Natural Resources. They were also shipped to 11 other states. Many of the boxwoods (Buxus spp.) were sold to consumers. The variety ‘Graham Blandy’ seemed to be particularly affected.

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Once a Purdue University lab confirmed the disease, DNR ordered the chain to remove all boxwoods from their shelves for disposal, and that the stores mitigate the area through disinfection to ensure that the pathogen is no longer present and able to infect further shipments of plants, the DNR report says.

Plant drops leaves

Consumers likely already know they have a problem with their boxwoods. “The plants were shipped in early spring, so plants that were infected at shipment would likely be defoliating now,” said Tom Creswell, director of Purdue University’s Plant and Pest Diagnostic Lab.

A boxwood shows evidence of the blight, which quickly causes the shrub to lose its foliage.

This is a serious disease because the blight (Calonechtria pseudonaviculata) infests other members of the boxwood family, including the popular groundcover Japanese spurge (Pachysandra spp.). Another plant affected is sweetbox (Sarcococca spp.), which is not usually grown in central Indiana because the shrub is not winter hardy, but southern Indiana landscapes may have it.

This column first reported on this disease in 2012, when it was discovered in Ohio. The disease was first found in 2011 in Connecticut on boxwoods in a residential landscape. In the other states and Canada, the blight has been found on boxwoods at nurseries and growers.

Fast spreading disease

The alarms were sounded after researchers in Connecticut exposed healthy pachysandra plants to the spores of boxwood blight fungus. Within 10 days, the small round spots developed and within three weeks, the affected pachysandra leaves yellowed and dropped off. What that means is that besides being susceptible to infection, pachysandra will spread the disease. The disease is spread by spores via air or water. The disease also can be dormant and then erupt.

The fungus disease boxwood blight starts as dark round spots on the leaves.

The natural inclination would be to treat the boxwoods and pachysandra with a fungicide, but that’s not recommended. “The outcome will be disappointing at best,” said Janna L. Beckerman, extension educator and plant pathologist. Fungicides are preventative, not curative. If your plants are infected, fungicide will not help.

Fungicide applications are only recommended when a known disease is present or you are spraying routinely to protect from a disease you know will show up every year, such as apple scab on apples or septoria leaf spot on tomato, Creswell said.

For more information, download Purdue’s “Boxwood Blight” publication (http://bit.ly/2NN8CXv). If you suspect your boxwoods have blight, send a sample to Purdue’s Plant Pest and Diagnostic Lab (http://bit.ly/2qEo6p2).

The state has a web page devoted to this disease (http://bit.ly/2QTNr8e), and asks you to call 866-663-9684 if you suspect one of your plants shows signs and symptoms of boxwood blight.

Jo Ellen Meyers Sharp (hoosiergardener.com) is vice president of Garden Writers Association and co-author of “The Indiana Gardener's Guide.” Write to her at P.O. Box 20310, Indianapolis, IN 46220-0310, or e-mail thehoosiergardener@gmail.com