There is a new, imported disease threatening Virginia landscapes. The disease is known as Boxwood Blight and was first documented in Carrol County, Virginia in 2011. It has since been found throughout Virginia including at the Woodrow Wilson Birthplace in Staunton.
What is Boxwood Blight?
The disease is believed to have come from Europe where it is a significant disease. It is caused by the fungi Calonectria pseudonaviculata. Symptoms of Boxwood Blight include leaf spots which are generally circular in shape. These light to dark brown spots may coalesce to cover the entire leaf. In addition, black streaking and lesions are seen on the stems and limbs. The plant may also show downy white tufts which are the fungal fruiting bodies of the disease.
As the disease progresses, the plant will defoliate starting at the base and moving upward. Often the plants will have bare limbs with tufts of leaves on the top giving a “lions tail” look. Positive diagnosis can be made through laboratory testing. Check with the Virginia Cooperative Extension Service for proper procedures to submit a sample for testing.
Boxwood Blight is spread through the spore which can attach to any surface. This includes landscape equipment and tool, clothing or on animal fur. Because of this, there are many modes of infection. Care must be taken to disinfect pruning tools to reduce the risk of transferring the disease.
One of the primary modes of spread is through nursery stock and clippings. Be sure to inspect any new Boxwood plants and insist they are from certified nurseries before you plant them in your landscape. In addition, greenery in holiday decorations could have infected Boxwood. When disposing of these decorations, double wrap in plastic bags and dispose of off-site, do not compost this material. Also, all pruning debris must be disposed of off-site. The spore from this disease can survive up to six years.
The infection will form and spread when the plant is wet and the spore is able to contact the plant and leaves. Heavy rain, wind-driven rain, and overhead irrigation are the primary means of infection. This disease prefers wet, warm conditions (45-85 degrees Fahrenheit) with the ideal temperature for infection being 77 degrees Fahrenheit.
So, what can be done?
At this time there is no cure for the disease so the only course is prevention.
First, good cultural practices that improve the overall health of the plant are essential. These include proper pruning to thin and open the canopy. This disease, as with others, thrives on closed canopies which maintain high humidity and low air flow. Prune out dead and diseased limbs in the dormant season to open the canopy as much as possible.
Next, clean out all leaf litter under and around the plants as these may harbor the spores. Mulch with good organic mulch to maintain soil moisture and plant health.
Finally, use fungicide treatments as a preventative. There are several products available that have shown good results in prevention. As previously mentioned, there is no cure so it is imperative to do all you can to prevent this disease. These fungicide treatments must be continued on an annual basis and require multiple treatments each year.
So, the bad news is that one of the most important plants in Virginias Landscapes is under attack and we will lose many valuable plants. But the good news is Big O Tree and Lawn Service offers pest management plans to assist in the prevention of this disease. If you are careful and vigilant you can protect your plants.
As always, contact us if you have any questions about this devastating disease or if you would like to have your Boxwood inspected. Our team will develop a program designed for your unique needs.