Boxwood blight can be devastating to American boxwood cultivars, which are common in the Kentucky landscape. Complete defoliation can occur within a week and plants can die within a single growing season. Use of tolerant cultivars, cultural practices, and fungicides can reduce incidence and spread of boxwood blight.
Boxwood Blight Facts
- Symptoms on leaves can appear as light or dark brown circular leaf spots with darker borders (Figure 1). These symptoms often go unobserved due to rapid defoliation. Defoliation of the lower plant canopy is often the first obvious symptom of boxwood blight (Figure 2).
- Dark brown or black streak-like lesions appear on infected stems (Figure 3).
- Favored by warm, humid weather.
- Caused by the fungus Cylindrocladium buxicola.
- The pathogen can survive buried in soil for 1 year and on plant debris for at least 6 years.
- The disease may be spread by splashing water, wind, tools, clothing, and wet hands. Long distance movement is reliant upon the transport of infected plants, infested soil, or contaminated equipment.
If boxwood blight is suspected, contact a local county Extension agent, who may submit a sample to the UK Plant Disease Diagnostic Lab for confirmation.
The following management options are recommended:
- Inspect plants prior to purchase, and do not install any plants with an unhealthy appearance.
- Plant boxwoods with disease tolerance, such as:
- Buxus microphylla japonica ‘Green Beauty’
- Buxus sinica insularis ‘Nana’.
- Increase plant spacing to allow for air movement.
- Minimize overhead watering.
- Homeowners can utilize fungicides containing chlorothalonil or tebuconazole to protect plants from infection or suppress disease development. Always follow label directions when utilizing fungicides.
- If plants become infected, remove them from the landscape immediately. If boxwoods grown for commercial sale are infected, they should be destroyed and not sold.
- Boxwood Blight (PPFS-OR-W-20)
- Homeowner’s Guide to Fungicides (PPFS-GEN-07)
- Landscape Sanitation (PPFS-GEN-04)
By Kimberly Leonberger, Plant Pathology Extension Associate, and Nicole Gauthier, Plant Pathology Extension Specialist