Boxwoods, one of the most popular foundation plants in Southern landscapes, needs special attention during our wet spring. Boxwood blight, a new ornamental disease affecting plants in the boxwood family, may soon be heading to a landscape near you.
While boxwoods are known to be fairly tough landscape plants, this pathogen is sure to leave a path of destruction wherever it shows up.
The fungus causing boxwood blight, Calonectria pseudonaviculatum, has been found in landscapes throughout Georgia. Boxwood blight was first identified in the U.S. in 2011 and has since been found in 20 states. While the pathogen can be spread in a variety of ways, it mostly travels between states and regions through the movement of infected plants.
Dwarf English boxwoods are highly susceptible to the disease, as are the American, or common, boxwoods. Cultivars of the Korean and Japanese boxwoods appear to be slightly less susceptible. None of the commercial boxwood cultivars are immune to this disease. Other plants within the Buxaceae family, such as pachysandra, also can be affected.
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According to Jean Williams-Woodward, a University of Georgia plant pathologist, initial symptoms include circular, tan leaf spots with a dark purple or brown border. Often, black lesions, or sores, also are seen on the stems. As the disease progresses, infected leaves become tan and fall from the plant. Rapid defoliation is a symptom of boxwood blight.
Shady environments, humidity and warm, wet environments tend to favor disease development. Leaves must remain wet for 24-48 hours for disease initiation to occur. While the fungus can be killed at higher temperatures (seven or more days at 91 degrees or hotter), it has the ability to produce structures (microsclerotia) to survive adverse environmental conditions.
The disease is spread primarily through infected plants and debris, such as leaves. While the white tufts of sticky spores aren't spread by wind, they can readily be transported by animals, shoes, hands and tools (such as pruners and shovels).
Exclusion is the best control option available. Inspect all boxwoods for disease symptoms prior to planting in the landscape. Consider having a quarantine area as new plants are introduced.
Do not introduce the disease on tools and pruners. Disinfect tools frequently. Mix 2 1/2 tablespoons of Lysol Concentrate Disinfectant (5.5 ppercent) per gallon of water and pour into spray bottles. Spray tools and allow them to dry for maximum effectiveness.
If boxwood blight is detected in the landscape, the plant and debris need to be bagged, secured tightly and disposed of (landfill) as quickly as possible. Leaf debris can be bagged, buried or burned on-site. Do not compost.
This disease cannot be cured with fungicide treatments. Products containing chlorothalonil or fludioxonil can be applied as preventatives before the onset of the disease. Suspect samples can be submitted to your local Extension office for submission to the UGA Plant Disease Clinic. Homeowner prices vary per office, but there is usually no charge for samples submitted by landscape professionals. If you are interested in this and similar topics, consider joining us for Green-up 2016 (see below for information).
Green-up at Middle Georgia State University on March 4. While this event is geared toward the green industry and landscapers, all are welcome. Topics covered by UGA specialists will include turf grass, turf disease, weed control, pesticide safety and diseases of ornamentals. Six hours of category 24 re-certification credit is available. Contact us at 478-751-6338 or firstname.lastname@example.org for more information.
Cheery Cherrys: Keeping Macon's Trees Happy: 5:30 p.m. March 8, Washington Library, 1180 Washington Ave. Free. Contact us at 478-751-6338 for more information.
Contact county Extension agent Karol Kelly at email@example.com.