Half of my Japanese boxwood is turning brown and dry. It seems to be dying. The other half of those bushes are doing great as far as I can tell. All are on the front (west) of my house. The ones that are thriving get more sun, but definitely not total sun. I pruned the dead branches out of the dying shrubs this past spring, but the rest continued to turn brown. Is there anything I can do to bring the unhealthy bushes back to health?

There is no way that I can tell you what has happened to your boxwood. If I had to venture a guess, it would be the severe drought conditions of the past two years. See also the information from the Texas Plant Diseases Handbook which can be found at this Aggie Web site:

Buxus spp.

Decline, Dieback, Root Rots, Twig Blight, Cankers (fungi - Armillaria spp., Fusarium spp., Gandoderma spp., Nectria spp., Phymatotrichum spp., Rhizoctonia spp.): Infected branches often start growth later in spring than normal ones. Leaves on such branches usually curl upward close to the stem and turn light grayish-green or bronze and finally straw-colored. Leaves may wither and drop early leaving bare twigs. Roots may be decayed. The bark at base of branches may die and slough off. Before growth starts in spring, remove and destroy all leaves on ground and lodged in twig crotches. Prune out dead twigs and severely cankered branches as soon as noticed. Spray with a fungicide just after removing dead leaves and branches and as new leaves begin to develop.

Leaf Spots, Leaf Tip Blights, Leaf Cast (fungi - Diplodia spp., Phomaspp., Phyllosticta spp.):
Leaves variously spotted may become pale or straw-colored, sometimes dull tan or brown, starting at margins and tips. Many leaves drop early. Young twigs may die. Begin spraying with a foliar fungicide as new leaves emerge.

Nematodes (Lesion, Ring, Stubby Root, Stunt and Root Knot): Plants are weakened, stunted and lack vigor, may wilt on hot days and recover at night. Leaves may be pale green to bronze or orange. Plants gradually decline and branches may die back. Roots will be stunted, often bushy, dark and may have knots or galls on them. Fumigate planting site before replanting boxwood in infected soil.

Root Knot (nematode - Meloidogyne spp.): Plants usually lacking vigor are often stunted and yellow. Small-to-large swellings, galls or knots develop on the roots. These are usually round and cannot be broken off like nodules on legume roots. This is a major limiting factor in growing boxwood.
Root Rot (fungus - Phytophthora cinnamomi): Foliage has an off-color followed by sudden wilting and death of the entire plant. Usually infected plants cannot be saved. Winter Injury (non-pathological): Leaves may turn bronze colored, rusty brown or red with dead areas around margins. Leaves will usually begin to dry in the late spring. Leaves, twigs and even entire plants may die back. Plants that are not watered during the wintertime are more susceptible to winter injury. Using mulches around the plants will help prevent freezing.

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