Boxwood Blight Suspected in Wilkes County
Boxwood blight is a highly transmissible fungal disease caused by the Cylindrocladium buxicola fungus. It affects boxwoods, both English and other Buxus varieties. Sweetbox (Saracocca) and Pachysandra groundcover species, both Japanese and Alleghany, are related to boxwoods and are susceptible to Boxwood blight. It has been tentatively identified in a home garden in North Wilkesboro in the last week. The symptoms started a couple of weeks back and the disease has spread rapidly to nearby boxwoods. Infected tissue is currently being analyzed in a laboratory setting for confirmation.
Boxwood blight was first identified in North Carolina in 2011 and is largely spread by movement of plant material, including on boxwood cuttings used for wreaths and infected plants coming from nurseries. Plants may carry the spores but not show symptoms if they are a resistant variety, or if fungicide has been applied, or if conditions are not right for the disease to spread. The disease will only spread when conditions are right, with warm and humid conditions when there are prolonged periods of leaf wetness or frequent rainfall during the summer, as we have experienced lately.
Symptoms may include brown or black spots on leaves, rapid discoloration of leaves, leaf drop, and black streaks on the woody tissue. Symptoms tend to progress rapidly, with the time between initial leaf spotting and defoliation being only a few days. Spores can travel on clothing, tools, tires, shoes, animals, and plant material. Anyone who suspects they have boxwood blight should contact your County Extension office to help with diagnosis.
While boxwood blight does not necessarily kill a plant, the defoliation and risk for re-infection mean that removing the plant can be the best solution. To remove, cut the plant at the base, rake up all leaves and debris, as much as possible, and remove from the landscape in a sealed container such as a plastic bag. Either burn all residue in a safe and legal location, or carry plant material to the landfill. Be sure to check in with the landfill for their specifications before hauling. The container or bag you carry residues in to be completely sealed.
Since humans and pets can also transmit the spores, wash any clothing thoroughly after coming into contact with infected plants. Wash off and sanitize tools with Lysol spray or 70% alcohol. Be sure to alert any landscapers of an infection or possible infection. Landscapers should take extreme precautions with sanitizing vehicles and tools after coming into contact with Boxwood blight, whether it be hauling infected material or mowing lawns in areas where there are infected materials.
Because it is difficult to know when boxwood blight will start to spread or if there may be spores present close by, gardeners should take care to prevent boxwood blight on any prized or valuable plantings of boxwoods or other susceptible plants. Apply a fungicide with the active ingredient chlorothalonil every 10-14 days, during humid conditions throughout the warm season. This could be as long as mid-April into October, depending on the year.
In areas where plants have been removed due to Boxwood blight, you can replant with non-susceptible species. Japanese hollies are a good option for well-drained locations. Buxus microphylla ‘Golden Dream’, Buxus harlandii, Buxus sinica var. insularis ‘Nana’
Buxus microphylla var. japonica ‘Green Beauty’ are the most resistant related species and are recommended for re-planting where there has been an infection.
Boxwoods vary in their susceptibility so you may see the disease on some but not others, if you have a mixed planting. Or the disease may progress more rapidly on highly susceptible types, or cause infection but not as severe on less susceptible varieties. If you have questions about your specific variety, or if you suspect you may have boxwood blight, contact your County Extension office for further instructions.