The first step in treating a boxwood problem is identifying the cause
Question: I have several boxwoods planted around the house. There are a few brown patches and dead branches on them this spring. Could these just be damage from the winter or could there be something else going on? Should I just prune them out?
Answer: Boxwoods (Buxus species) are terrific broad-leaved evergreens for the landscape, but they can sometimes be problematic. Some species have more issues than others.
The brown spots and dead branches on your boxwood may be because of several common boxwood ailments.
If the brown patches and dead foliage are primarily found at the tips of the branches, the likely culprit is winter damage. Boxwoods sometimes produce new growth late in the season, especially if they’re pruned in the summer, and this new growth is highly susceptible to winter damage. Depending on the severity of the winter, damage may also appear on the older growth.
Winter damage should be pruned out of the plant with a clean, sharp pair of pruners within the next few weeks. As with all pruning, the equipment should be disinfected with a 10-percent bleach solution, rubbing alcohol or Lysol before pruning each new plant.
If the damage appears as small brown blotches at the center of the leaves with a paler, blisterlike spot at the center, boxwood leafminers may be the culprit.
These tiny insects overwinter as larvae between leaf tissue and emerge as adults in May. They then breed and start a new generation that feeds on leaf tissue through the summer.
Boxwood leafminer injury can be extensive and occurs on both old and new leaves, and the blisterlike spot is very distinctive. Many times, the leaves will fall off. To control boxwood leafminer, plant resistant cultivars when possible, don’t overfertilize plants and prune off the infected leaves before the adults emerge in May and discard them. You also can apply neem-based organic pesticides in late May and early June to discourage egg-laying behavior.
A third possible problem for boxwoods is by far the most devastating. Boxwood blight is a fungal organism that is a recent introduction to Pennsylvania. The spores are easily spread on the wind and in water droplets, as well as on birds and other animals, including people.
Symptoms of boxwood blight are very distinctive. In mid to late summer, dark circular spots occur on the newest foliage. Over the next few weeks, the spots grow and develop concentric rings. By fall, the spots merge to form lesions, and black streaks occur on the stems. On the underside of the leaves, there will often be white fungal spores. Leaves eventually turn completely brown and drop off the plant. There is no cure for boxwood blight.
Because this disease spreads so rapidly, sanitation is key. Don’t work with wet plants, and carefully disinfect all pruning equipment between plants. If you think you may have boxwood blight, it’s very important to send a sample of the plant to the Penn State Plant Disease Clinic for confirmation. You can contact them at 814-865-2204 or at plantpath.psu.edu/facilities/plant-disease-clinic.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com.
Send your gardening or landscaping questions to [email protected] or The Good Earth, 503 Martindale St., Third Floor, Pittsburgh, PA 15212.