Top: Affected pachysandra. Bottom: Affected boxwood.
The many rain days we’ve experienced the last several weeks have helped plants and lawns grow green and lush… but they also have brought out a lot of the common disease called Volutella. Even though the prevalence of Volutella Blight of Pachysandra & Boxwood has increased over the past few years, it is very treatable. The increase is more than likely due to having a wet spring, like this year, and those of the few recent years. It is common to notice brown dieback on your pachysandra groundcover and evergreen boxwood. While this may have originated from a few different circumstance or factors, Volutella may be the cause.
Pachysandra Symptoms and Disease
Pachysandra is a common groundcover plant. The most common disease affecting this plant is Volutella blight (sometimes called leaf blight and stem canker), caused by the fungus Volutella pachysandrae. Volutella blight usually first becomes visible as wilting or dead patches in the pachysandra bed. Individual plants develop irregular tan to brown lesions on the leaves, often with concentric rings, which eventually grow and coalesce until the entire leaf dies. Brown or black cankers develop and girdle the stems, causing the plants to wilt and die. During humid weather in late spring and summer, small pinkish spore-producing structures of the fungus appear in the stem cankers and on the undersides of leaf lesions.
Stresses such as insect infestation, winter injury, excessive sun exposure, drought, or recent trimming make pachysandra more susceptible to Volutella blight, so minimizing plant stress is the first step in managing this disease. Sanitation is another important management tactic, so plants affected by Volutella blight should be removed. The disease is encouraged by moist, humid conditions, so practices that reduce leaf wetness and humidity can help to manage Volutella blight. Occasional thinning of the bed, watering in the morning rather than the evening, and avoiding heavy mulch can help. Several fungicides may be used for Volutella blight management preventatively, including thiophanate methyl, chlorthalonil, and mancozeb. Plants should be sprayed first when new foliage emerges in the spring, and repeated following label directions.
Boxwood Symptoms and Disease
Boxwood Volutella stem blight or canker is caused by the fungus Pseudonectria rouselliana on boxwood (Buxus spp.). Volutella buxi is the name for the imperfect stage of the fungus (the imperfect stage produce asexual spores called conidia).
In moist weather, numerous clusters of conidia appear as salmon-pink colored masses through the bark on stems and on leaves. The distinct color makes this the most distinguishing symptom. The volutella stem blight causes stem tips and twigs to die back. Cankers may form on the branches or at the soil line. Foliar symptoms are similar to those caused by winter injury. Leaves will turn orange to bronze and then straw-colored in the middle or the top of the plant. If winter injury alone is the problem, new, healthy leaves will appear in spring and eventually hide the bronze-colored leaves. The volutella fungus infects wounds caused by winter injury from heavy snow load on the branches. The fungus usually enters through cracks create at the branching junctions. The first noticeable symptom is that certain branches or certain plants in a group do not start new growth as early in the spring as do others, nor is the new growth as vigorous as that on healthy specimens. Infected leaves turn upward and lie close to the stem instead of spreading out like the leaves on healthy stems. The bark at the base of an infected branch gets loose and peels off readily from the gray to black discolored wood beneath. Volutella usually does not kill boxwoods, but can disfigure them.
Pruning before new growth begins allows it to fill in the bare spaces. Dead branches should be removed as soon as they are noticed. Prune out infected branches to healthy tissue and discard. The annual removal and destruction of all leaves that have lodged in crotches of branches is also recommended. Pruners should be dipped in alcohol or bleach water between cuts to prevent spreading the disease healthy plant material. Apply systemic fungicides like immunox or infuse every 14 days in spring before and during new foliage emergences; or contact fungicides like copper sulfate every 7-10 days and after rainfall to prevent inoculation. The first application should be made before removing the dead leaves and dying branches to prevent the spread of the disease during pruning.
Proper diagnosis and care will help to strengthen the health of your pachysandra and boxwood plants. Early diagnosis is vital for a quick and full recovery. For further information about this or other plant diseases, please contact Nature’s Perspective.