We’ve had a wet spring and the warm temperatures and high humidity of summer have just begun. I am ever vigilant for diseases in the garden at this time of the year. One fungus that is the stuff of nightmares is Boxwood Blight, a monster of a disease that has spread to 26 states. Defoliation of boxwood can occur suddenly, with complete leaf loss in severe cases. It has already destroyed generations-old box in my home state of Virginia.
Several Buxus species can be affected but it’s the English (Buxus semp. ‘Suffruticosa’) and American or common boxwood (B. sempervirens) that are most susceptible. Virginia Tech lists my variety as a Blight-Resistant/Tolerant Cultivar, but that’s not a guarantee. Affected boxwood can be treated commercially with fungicides but there is no absolute cure for the pathogen. Europeans have been fighting the disease for over 25 years.
Boxwood blight has been confirmed on nursery stock in New Hampshire so all NH box is at risk. Although there isn’t a cure as of today, commercial strength fungicides applied by professionals are most effective for treatment. There are limited products approved for amateur gardeners’ use. Once a month, I use a product from the Netherlands, Topbuxus, that I hope will make my box more resistant. It’s an effervescent tablet dissolved in water and sprayed on boxwood and said to “stop and prevent box blight.” It’s a super tonic for box and promotes good health but I’m unsure about its blight effectiveness. If anything, a healthy plant should resist diseases better.
- Inspect any newly purchased boxwood for symptoms of the disease, including leaf spots, leaf browning, black streaks on stems and leaf drop. Any boxwood that has these symptoms should be double-bagged and discarded in the landfill. Do not compost infected greenery.
- Plant in locations with good air circulation.
- Prune to increase air circulation.
- Sanitize pruning equipment before going from one plant to another. Lysol disinfectant works well.
- Water at a time of day that the plants will dry quickly.
- Avoid overhead watering if possible.
- If desired for a hedge or mass planting, it is best to plant loosely.