Much like downy mildew and dogwood anthracnose before it, boxwood blight is the latest disease to attack a plant favorite.
First spotted in the United Kingdom in the mid-1990s, boxwood blight (Cylindrocladium buxicola or Cylindrocladium pseudonaviculatum) is now thought to be prevalent throughout Europe. In October 2011, this same fungus was confirmed on boxwoods in Connecticut landscapes, garden centers and nurseries. Blight has since been spotted in North Carolina and Virginia, and there’s been one find in the Western United States, as well.
Characterized by brown leaf spots with dark edges, blights, black cankers on stems, fruiting structures called sporodochia, defoliation and dieback, the disease attacks all boxwood species. The disease cycle can be completed within a week, and thrives best in warm, humid temperatures around 77 degrees.
Although there is no cure to boxwood blight, some best management practices may be employed to keep it from attacking your plants. The disease is spread through splash or wind driven rain. Sticky spores also make it possible for infected work equipment, leaf debris, tools, clothing, tires and other boxwoods to contaminate healthy trees.
Some best practices to keep boxwood blight off your crop include:
- Knowing the signs and symptoms of boxwood blight
- Scouting plants regularly
- Avoid purchasing young plants that were treated with fungicides, so that disease identification can be made upon arrival (for wholesale growers)
- Inspecting plants before unloading and rejecting problem plants immediately
- Paying attention to sanitation by keeping all equipment used on boxwoods separate
- Cleaning boxwood equipment by soaking in a 1-to-10 ratio of bleach to water or 70 percent ethanol solution for one to two minutes.
- Limiting entry of new plant material and not mingling new material with existing plants
- Confirming fungicides have been sprayed before the boxwood is sent, so retailers and consumers have extended protection (for wholesale growers selling to their customers)
Fungicides, while unable to cure the disease, may limit its spread. But because the disease is so new to the United States, there have not been major trials done to this point to determine how effective existing fungicides are on boxwood blight. Newer chemicals require boxwood owners to rotate the use of chemicals to avoid disease resistance.
North Carolina State University’s Kelly Ivors has developed a short list of potentially useful fungicides based on parallels with other diseases, including:
- Medallion (Syngenta)
- Palladium (Syngenta)
- Pageant (BASF)
- Terragard 50W (OHP)
According to BASF’s Kathie Kalmowitz, Pageant uses two active ingredients to target several diseases including cylindricadium.
“It was in the English trial, and thus, there is some precedence to having our product,” Kalmowitz says. “Dr. Ivers has been asked to do a containment trial. She will be testing all of these in a U.S. trial. We all look forward to her work this spring.”