Boxwood owners have been hearing for a few years that there is a new disease coming that may impact their landscapes.
This disease is boxwood blight. It’s due to a fungal plant pathogen with the $10 name of Calonectria pseudonaviculata.
This is a very serious fungal disease that only affects members of the Buxus plant family, primarily boxwood. It can also infect pachysandras as they are also members of the Buxus family.
There have been multiple cases of this disease confirmed in Danville over the past two months. There are probably more infected boxwoods out there, and we just haven’t learned of them as yet.
This disease causes rapid defoliation and decline of most boxwood cultivars. Right now, there is no cure for this disease. Research is being conducted, but there is nothing to show for it other than some important practices that may help prevent the spread of the disease to adjacent plants.
The symptoms are easy to recognize.
For most gardeners, the first thing they notice is a large volume of green leaves on the ground. The next thing they see, when they look a little higher, is bare branches. Many of those bare branches may have black streaks and there occasionally may be some white material if the fungus is producing new spores. A closer look at the remaining foliage that surrounds the bare branches will reveal leaves with large dark brown or black spots.
These symptoms, taken together, are a sure sign the boxwood is infected with boxwood blight.
Any infected boxwoods should be removed immediately to reduce the spread to adjacent boxwoods that are not showing any symptoms yet. All of the leaves and other debris on the ground must be removed as well.
The fungal spores can live for up to five years or longer and can infect any boxwood they come in contact with. Any tools used to remove the infected boxwoods must be sterilized after the work is done. A contaminated tool is one of the methods this disease uses to find new victims.
Another is lawn mowers cutting up infected leaves. The spores of boxwood blight are sticky and will attach to anything they come into contact with and then can be transported to healthy shrubs nearby.
Do not put boxwood cuttings into a compost pile. The preferred method of disposal is to burn them, but that may not be legal in all locations, especially in the city. If nothing else, put them with the yard waste, but do not use any of the free mulch or compost from the city’s compost site anywhere near healthy boxwoods. We suspect there have already been diseased boxwoods that were taken to the compost site and contaminated the material there with the disease pathogens.
If you use this mulch, you can ruin your neighbor’s boxwoods as well as your own.
Once the boxwoods have been removed it is probably best to avoid planting new boxwoods in their place. The site will still have some viable traces of the disease present.
There are some cultivars of boxwood that are showing resistance to the blight. In general, English and American boxwoods are most susceptible, except one or two of the upright, vertical growing cultivars such as “Dee Runk.” Some Korean boxwoods are resistant, but not all of them. There are varying degrees of resistance among the plants so that even a “resistant” boxwood may succumb to the disease.
For a complete list of resistant cultivars, visit to www.ext.vt.edu and in the search box in the top right corner enter boxwood blight.
You will get a list of current publications, select the one named “Best Management Practices for Boxwood Blight in the Virginia Home Landscape.” The list is on page two. If you purchase any new boxwoods be sure to buy only from a reputable nursery that has signed a best management practices agreement.
Unfortunately, we are just getting started with this disease. It will likely spread to more landscapes in the coming years. I examined the disease on one property and while I was there I found it had infected the boxwoods at three of the neighbors’ homes as well.
I have put together a two-page fact sheet on this disease for anyone who wants more information. Please visit our website at danville.ext.vt.edu or Facebook page to view this publication, or you may contact the Danville Extension office at (434) 799-6558 and ask for a copy to be mailed to you. Our office is located at 326 Taylor Drive, Suite 100 (the Health Department building) if you would like to pick up a copy.
It may be difficult, but try to enjoy your garden.