US: Boxwood blight found in holiday wreaths

Seemingly innocent holiday wreaths sold across the Palmetto State have been found to carry a devastating plant disease.

Boxwood blight, a fungal disease that can be deadly to the familiar boxwood shrub, was confirmed on wreaths containing boxwood cuttings from a single North Carolina nursery. From that nursery, sales of the wreaths have stretched from the mountains to the sea in South Carolina and reached as far away as Indiana.

“The good news is, it’s not lot of plants, it’s just cuttings. The biggest risk comes when people dispose of the infected wreaths after Christmas,” said Steven Long, assistant director of Clemson University’s Department of Plant Industry (DPI), a state regulatory agency that oversees plant nurseries and regulated diseases like boxwood blight.

“Those who obtained a Christmas wreath this year containing boxwood plant parts should treat it as infected and dispose of it after Christmas by burning or, even better, double-bagging it and including it with their trash for deposit in a landfill,” Long said.

Wreaths displayed outdoors are also a potential concern if they are exposed to the elements, Long said.

“The disease moves readily when water is present, so wreaths that are very exposed to rainwater or raindrops would be risky to keep in place if they are near landscape plantings of boxwood,” he said. “The disease could move with the water right down into the landscape beds. In contrast, wreaths used indoors would be harmless.

“What we’re worried about is the chance that the fungus may migrate into soil where it may infect other plants,” Long said. “It should not be disposed on people’s property, especially not chipping it and using it as mulch. As long as it goes to a designated landfill it will be harmless.”

Found throughout Europe, boxwood blight was first discovered in the United States in 2011. It has since appeared in at least 24 states. Its only prior detection in a South Carolina nursery was in 2016, where it was contained and destroyed.

Long said his office was notified of the diseased shipments by the Plant Industry Division of the North Carolina Department of Agriculture and Consumer Services. “We are extremely grateful that they reached us early in this process,” Long said, “because it gives us time to spread the word about containment of the disease.”

Direct sales from the affected nursery were traced and known infected wreaths have been removed. Long said it is possible that out-of-state brokers purchased some of the infected material and sold elsewhere in South Carolina, but that “there should be no risk in purchasing a wreath as long as it’s handled and disposed of with care.”

He added that some of sales to South Carolina were to school groups that used them in holiday fundraisers. The same was true for a Boy Scout troop in Indiana.

Caused by the fungus Cylindrocladium buxicola, boxwood blight attacks the above-ground portions of boxwoods, not the roots. It starts with light or dark brown spots or lesions on infected leaves, but can spread to stems, causing black cankers and twig death. Infected foliage often drops from the plant.

“Boxwood blight can be tricky to identify. The samples we found didn’t look suspect, but they tested positive,” Long said. “Even expert inspectors can have a difficult time detecting the disease on stems and foliage, so the safe thing to do in this case is to treat any boxwood wreaths this season as if they were infected and dispose of them properly.”

In the future, homeowners who believe their live boxwood plantings were exposed to the pathogen should contact their county Extension agent to confirm the disease and explore methods of containment.

“Boxwood blight can spread to damage all foliage and stems on susceptible boxwood cultivars. It is extremely detrimental to many boxwoods and almost always requires plant removal and extensive environmental cleanup,” Long said. “It easily can be confused with other diseases and disorders, but Clemson’s Plant Problem Clinic can analyze plant samples suspected of the disease. If you observe symptoms on your boxwoods, it is important to have the disease accurately identified by a specialist.”

Clemson’s Department of Plant Industry conducts certification and inspection programs related to plant nurseries and enforces state laws and regulations that protect the state from exotic and invasive species.

It is part of the university’s Regulatory Services branch, which includes departments that regulate pesticides and structural pest control, verify that fertilizer and lime meet standards and labeled guarantees, conduct seed and organic certification programs, diagnose plant pests and ensure readiness to respond to catastrophic events that impact the state’s agriculture.

Source: Clemson University (Tom Hallman)