English Dwarf Boxwood and Fungus

English Boxwood Decline

A fungus called Paecilomyces buxi attacks English boxwoods over 20 years old. Diseased plants lose their color and turn from dark green to light green, eventually fading to yellow and the roots rot. English dwarf boxwoods do not usually show foliar symptoms until the roots have severely decayed. Nematodes may have something to do with the disease since they are occasionally found on dying plant roots, but as of 2011 researchers are not sure about their role. Water-stressed plants are more susceptible than well-watered boxwoods, so keep plants watered during periods of drought.

English dwarf boxwoods cannot tolerate poor soil drainage or overwatering and root rot infections often attack plants that grow in constantly wet soil. The Phytophthora nicotianae and Phytophthora cinnamomi fungi cause symptoms similar to those of English boxwood decline. The foliage turns yellow and the edges roll inward, the bark peels back from the wood and the roots decay. Infected plants usually die. There is no cure for root rot, but you can prevent infections by planting your boxwoods in raised beds or well-drained sites.

The Volutella buxi fungus causes boxwood canker. English dwarf boxwoods lose their color, changing from green to tan and the diseased leaves stay close to the stem rather than stretching out. The bark peels away from the wood to reveal diseased and discolored wood and fungal bodies appear on the branches and foliage. Prevent canker infections with fungicides such as lime sulfur or copper, prune out dead branches and remove leaf litter to prevent the disease from spreading.

Several fungi cause leaf spot infections in English dwarf boxwoods. The margins and tips turn brown and sunken discolored spots appear on the top surfaces of the leaves, while black fungal fruiting bodies form on the lower surfaces or inside the spots. These infections rarely cause serious damage. The Macrophoma candollei fungus causes macrophoma, another leaf spot infection, that forms on dead leaves. This fungus usually occurs as the result of environmental problems or root infections.