Boxwoods (Buxus spp.) are one of the most frequent plant samples we receive in the clinic. Homeowners and landscapers are often concerned about the Boxwood Blight disease, caused by the fungus Calonectria pseudonaviculata (previously Cylindrocladium pseudonaviculatum or Cylindrocladium buxicola).
Boxwood Blight was first found in Ohio in 2012. For several years after this, it was a regulated disease, and any boxwood found to have the disease was removed and destroyed. However, as it has become prevalent in the landscape in the last couple of years, removal of all infected Boxwoods is no longer required.
Boxwood Blight often first presents itself as dark brown spots on the leaves. As the disease progresses through the plant, the leaves will rapidly drop. Additionally, the stems will develop black cankers. Under the right conditions, you may see spore masses forming on the underside of the leaves or on the affected stems. There masses are white a fuzzy or spiky in appearance. Beause this disease can cause such extensive defoliation of plants, it can be a major cause for concern for landscapers and homeowners trying to maintain the beauty of the Boxwood hedges. However, many of the Boxwood samples we receive from growers concerned about Boxwood Blight do not actually have this disease, but have one or many other fungal, insect, or abiotic problems.
The following pages are excellent resources for information about Boxwood Blight and other common pathogens of Boxwoods, including Volutella Blight, Boxwood Leafminer, and more.
If you suspect you have a pathogen on your Boxwood plant, please contact us or send a sample in for examination. Most fungal pathogens can be identified from a few cuttings that contain symptomatic but not completely dead leaves. Leaves should have some green tissue and some discolored tissue. We are generally not able to make a diagnosis from completely defoliated stems or only dry tan/brown leaves. It is always helpful to include root and crown tissue in the sample, as some diseases are present in this tissue but not the leaves. However, as this can be difficult to retreive, especially for homeowners who may not have lawncare equipment, we can always start with a foliar sample and request roots or crown tissue if needed later.
Buckeye Yard a & Garden Online - Browned Boxwoods (contains information and images of insect damage and abiotic damage on Boxwoods)