Phytophthora root rot is most likely to occur in poorly drained soils. When the soil is saturated, the fungus penetrates into feeder roots and moves up the roots causing a dark discoloration. The outer cells of rotted roots slough-off easily leaving only the central portion. In advanced cases the bark on the main stem just above the soil may also slough-off. Boxwoods that die should not be replanted with boxwoods since the disease is soil borne.
Chemical treatment has limited effectiveness.
Providing good drainage and optimum growing conditions is the most effective method of treatment. It only affects English boxwoods and is caused by a complex of fungi and cultural practices. Foliage symptoms develop over a period of one to several years. The earliest symptoms are slightly off-colored areas in the plant. Leaves of affected stems progressively turn bronze, orange, dull green and straw-yellow, finally turning brown with defoliation leaving a gray skeleton of twigs.