Boxwood beds should be well-drained and overwatering avoided. Management consists of removing infected plants available chemical control is best used as a preventative, but does very little once an infection has been established. Roots are often dark brown or black, sparse, and brittle, and the cambium (inner tissue under the bark) at the base of the main stems may also become discolored dark brown or black. In boxwood, Phytophthora can cause individual branch wilting and dieback (Photo 1) leaving isolated areas of pale green, then brown, shriveled leaves attached to the stems. There are many species of Phytophthora, some of which have a broad host range. Heavy, wet soils favor Phytophthora root rot. Image credit: Neil Bell, Pacific Northwest Pest Management Handbooks. Phytophthora root rot showing light green, wilting leaves followed by leaf death. Under moist, humid conditions, the foliage may develop distinct masses of pink to salmon-colored spores Phytophthora Root Rot ( Phytophthora spp.) Infected leaves turn tan, straw-yellow or bronze color in the spring. Volutella progresses down the stem, whereas winter injury happens seemingly at once. This fungal pathogen is often associated with stem and leaf tissues damaged from winter injury. The disease can easily be identified by the numerous black, raised fruiting bodies found on dead or dying leaves Volutella Blight ( Volutella buxii (asexual stage of Pseudonectria rouselliana)) Macrophoma is a weak pathogen that causes leaf spots and straw-colored leaves. Macrophoma Leaf Spot ( Macrophoma candollei) Snow insulates and protects foliage from desiccating winds and extreme cold temperatures. A “snow line,” or distinct line that separates the healthy green bottom from the damaged brown top can also be an indication of winter injury. Injury is most likely to occur southwest and windward facing sides of the plant. The pattern of injury can also help diagnose winter injury. Depending on a plant’s hardiness, location, and weather conditions, winter injury can damage the entire plant or just the branch or leaf tips causing leaves to become pale yellow/reddish-bronze. Frozen soil prevents the plant from taking up water resulting in “freeze-dried” burn symptoms. Winter injury occurs as cold, dry winter winds and/or direct sunlight causes moisture loss from the evergreen leaves. More about boxwood blight best management practices is available in this Boxwood Health Production and Landscape Management guide. While these businesses may offer plant advice as a service to their customers, they are extremely cautious and go to great lengths not to introduce or spread this disease. Never take a suspected boxwood blight sample to a garden center, nursery, or other areas that may grow or distribute boxwood. If you suspect boxwood blight, we recommend you contact the University of Illinois Plant Clinic for information on how to submit a sample. A microscope is needed to confirm the disease diagnosis.Ĭommon boxwood blight look-alikes: winter Injury, Macrophoma leaf spot, Volutella blight, Phytophthora root rot, Fusarium canker, boxwood leafminer, and potentially boxwood psyllid.įortunately, these look-alikes cause a relatively minor injury that can be pruned out during a dry period of spring weather. Boxwood blight causes extensive defoliation, while look-alike disorders tend to have leaves turn tan to brown, but remain attached to the plant. One major difference between boxwood blight and its look-alikes is the potential for defoliation. Many of the symptoms associated with the disease are similar to other common boxwood disorders. Boxwood blight can be a challenging disease to identify outside a plant diagnostic laboratory. With the recent detections of boxwood blight, which is a regulated plant disease, in Illinois, the importance of scouting landscapes and new plants for the disease is greater than ever.
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