Boxwood blight is a potentially disastrous fungal disease that is beginning to affect boxwoods throughout Long Island but mainly concentrated on the east end where boxwoods are used heavily in landscapes. It harms English and American boxwoods severely, but also infects other varieties and also infects pachysandra. Unlike volutella blight, which is also a disease of boxwoods, boxwood blight will cause extensive leaf drop and defoliation. There is no viable technique to eradicate this disease, so our best practice will be to try and prevent spread, isolate and remove infected plants, and use preventative fungicide treatments on all other plants.

Infected plants show brown or black spots on leaves and long skinny black cankers on year old stems. The disease will usually result in leaf drop, sometimes within 2 weeks Whole plants or sections of plants may be affected. Cornell Cooperative Extension recommends a lab diagnosis of suspected tissue, followed by removing infected plants and bagging them along with all leaf litter on the ground. If you place infected rogued boxwoods in a waste pile, the spores will continue to live and affect other plants

The most likely avenue for spreading the disease is through bringing in infected plants. Water is also the main method of transportation, especially windblown water. Boxwoods that will be prone to infection are those that stay wet from overhead irrigation, lack of sunlight, or lack of air movement. The spores are large and “heavy” so they are not easily transmitted by air alone, but water droplets carried by air will spread the disease. Therefore, a hurricane or thunderstorm may cause an explosion of the disease at some point. The disease is most active between 50⁰ and 74⁰, with 74⁰ being optimum. The disease will grow rapidly on a 7 day cycle and generate new spores, even after killing its’ host. The spores are known to survive up to 6 years.

Preventative fungicide treatments to uninfected boxwoods will probably be the best precaution. This must be done from May until July and from September to October (these are the most active periods, the disease doesn’t like hot weather.) Treating infected boxwoods will not cure or eradicate the disease, but may mask symptoms temporarily if the plant hasn’t already defoliated.

If you think you have an infected or possibly infected shrub, call a Fox Tree arborist immediately. We’ll try to get a cutting to Cornell for ASAP diagnosis and then arrange to have the plant rogued and bagged. Try to avoid contact especially if the boxwood is wet. You don’t want to carry spores to your other plants.

If you have boxwoods at your property and are concerned about keeping them healthy, we highly recommend that you call us today to arrange an inspection aboxwood blight preventionnd to get yopu on a preventative program. Call us at (631) 698-2929