The Connecticut Agricultural Experiment Station (CAES) recently reported a new-to-Connecticut boxwood disease, a fungus called Cylindrocladium pseudonaviculatum. Sounds ominous, doesn’t it? Wait till you learn more.
According to facts and photos in the boxwood blight fact sheet prepared by Dr. Sharon M. Douglas, of the Department of Plant Pathology and Ecology at CAES, the disease is as ominous as it’s Latin name sounds.
Early stages of boxwood blight first appear as dark or light leaf spots or lesions, often with dark borders. The spots grow to cover more of each infected leaf causing leaves to turn brown or straw colored. Defoliation is likely to occur shortly after leaf symptoms develop.
Infected stems show dark brown to black lesions, sometimes with a diamond-shaped pattern. Lesions run from the soil line to the stem tip.
The fungus does not appear to affect boxwood roots but, as the plant sends up new growth in response to defoliation, new growth becomes infected from remnants of the fungus. Repeated regrowth and reinfection weakens and eventually kills.
Check out the disturbing photos in the boxwood blight fact sheet of all disease stages or watch this YouTube video.
Boxwood blight spreads rapidly in warm, humid conditions – think greenhouses and hoop houses. It loves temperature ranges of 64 to 77 degrees Fahrenheit (77 being optimum) but can die after seven days at 91 degrees Fahrenheit. It may also live up to five years on decomposing boxwood leaves.
Boxwood blight spores spread by wind, wind-driven rain and water splash and, since the sticky spores easily attach to clothing, boots, tools, and animals, spores can also be spread via human and animal movement.
So, what can one do? Since the disease is newly identified in Connecticut CAES recommends we
- Buy disease-free material from reputable nurseries and carefully inspect all plants before purchasing.
- Isolate newly purchased plants for at least one month and preferably for several months.
- Space plantings to maximize air circulation.
- Avoid overhead watering and working among plants when they are wet.
- Remove boxwood leaf debris from around plants.
- Become familiar with symptoms by studying images of the disease in the links above.
- Inspect for symptoms each week. If detected, immediately pull and remove entire plant and dispose of infected material in plastic bags. Do Not Compost.
- Stay in touch with CAES for the most current information on control. Of note: Boxwood blight has been common in England and other countries for years and has not been controlled by fungicides.
If you suspect boxwood blight follow these instructions for submitting samples to CAES for diagnosis.
The disease has been found in Hartford, Middlesex, Fairfield and New London counties in Connecticut. Since one of these counties is mine and I already have a fair number of boxwood planted in my deer-accessible gardens (boxwood are one of the few shrubs my local deer don’t yet eat), I’m going to watch my boxwood closely.