Buxus sempervirens is commonly referred to as boxwood. It is a broadleaf evergreen that grows in full sun to part shade. It is hardy in USDA zones 5 to 8. It prefers evenly moist but well drained sandy-clay soil. Boxwoods normally grow 5 to 15 feet tall. They bloom a light green/cream colored flower in April or May. Boxwoods can experience a number of problems with pests and diseases.
The boxwood leafminer is a small fly that attacks American boxwoods. Infected boxwoods develop sores on the bottom of their leaves. This causes the leaves to grow smaller, develop different coloring and fall off faster than normal. A serious infestation causes thin foliage and poor color over the entire boxwood. There is one generation of leafminers a season. In early spring, the adults emerge during a two-week period. This is at about the same time the boxwoods have started developing new growth. The flies invade the boxwoods and lay eggs on the leaves. The larvae recommence eating in the spring and the cycle begins again. Leafminer control involves using a pesticide in early spring, just as the flies begin to appear. For specific types of pesticides consult a garden center or university extension service.
Eurytetranychus buxi or boxwood spider mites are tiny, making detection of early symptoms difficult. The adult is only about 1/64 of an inch long. Spider mites also overwinter their eggs on the underside of leaves. The eggs then hatch in spring, develop rapidly and breed speedily, producing eight or more generations per year. The mites feed on boxwoods at all stages of life, eating on the leaf surfaces. They pierce the leaf and suck the sap out. In addition, while piercing, they also inject toxic saliva which infects the upper leaf with yellow spots. Mites prefer second- or third-year leaves and after infestation a boxwood looks unhealthy, dingy and grayish-silver color. Natural control occurs with mite enemies, such as ladybird beetles or other insects. Insecticides can be used, but determination of the infestation should be made first because the insecticide will also kill the natural predators. Consult a garden center before using chemicals on this pest.
Root rot is caused by the fungi Phytophthora nicotianane and P. cinnamomi. The leaves turn from a normal dark green to a paler green as the plant weakens. The roots become dark and rotted. The bark rots too, and peels off. Death of the entire infected plant is typical of this disease. Root rot occurs more frequently in wet and warm soil. It is worse in clay or poorly drained soil. Long periods of rain also contribute to this disease. Root rot has to be prevented as chemicals are not effective in controlling the disease once the symptoms spread above ground.