Pathogen
Coccinonectria pachysandricola
Hosts
Pachysandra procumbens (Allegheny pachysandra/spurge)
Pachysandra terminalis (Japanese pachysandra/spurge)
Sarcococca species (Sweet box)
Note that Volutella blight of boxwoods is caused by different fungal species, Pseudonectria buxi and Pseudonectria foliicola. All of these fungi once belonged to the genus Volutella, hence the common name of the diseases they cause.
Symptoms and Signs
Coccinonectria pachysandricola is an opportunistic pathogen and is most often found on plants injured by insect feeding, winter desiccation, excessive pruning, or those suffering from nutrient and water stress. The disease is usually not severe but if left untreated it can cause serious injury to established beds when other stresses are present.
Volutella blight of pachysandra begins as tan lesions with brown concentric rings on leaves and stems. Leaf lesions often coalesce, leading to partial or complete defoliation. Coccinonectria also produces destructive stem cankers that disrupt water and mineral transport, causing parts of the plant above that point to turn brown and die. Salmon-colored pads of fungal tissue can often be observed on the underside of infected leaves and on blighted shoots. These pads produce masses of spores. Wet, humid weather is conducive to disease development and whenever weather conditions are favorable the pathogen will grow and reproduce. Because pachysandra plantings are low to the ground and dense, they represent ideal conditions for disease development once the pathogen is established.
Management
Successful intervention involves a combination of sanitation, modification of the growing environment, disease resistance, and fungicide treatments. Prune out and discard blighted plant parts to reduce overwintering fungal structures. Dead plant parts harbor the pathogen and allow it to disseminate spores in very close proximity to newly developing tissues next spring and summer. Avoid pruning during wet periods, as the fungus will readily colonize these wounds. Limiting drought stress is important but free moisture on shoots and foliage promotes disease development; therefore, use drip irrigation or water plants early in the day to prevent extended periods of leaf wetness. Protect plants from exposure to winter sun and desiccation using mulch that does not hold moisture such as straw. Consider replacing Pachysandra terminalis with P. procumbens, which is less susceptible to Volutella blight.
Fungicides labeled for use against Volutella blight include copper salts of fatty and rosin acids, copper hydroxide, thiophanate-methyl, chlorothalonil and mancozeb. Carefully read and follow all label instructions on any fungicide you use. Chlorothalonil is a restricted-use chemical in Massachusetts and should never be used near water. Fungicides are most effective when applied prior to symptom development in the spring when newly emerging tissues appear. Later in the growing season, fungicides will have a reduced impact.