Volutella Stem Blight

Causal Agent

• The Volutella pachysandricola fungus causes the disease. Once infection occurs, it spreads rapidly with the help of fungal spores that continue affecting healthy plant areas all through the active growth season. Fungal growth is most rapid during moist, warm weather conditions in the spring and summer.

Favorable Conditions

• The fungus causing volutelle is an opportunistic pathogen primarily affecting poorly growing plants already under cultural stress or suffering from other diseases or pest infestations. Plants deficient in minerals or damaged by winter drying and sunscald are also more prone to infection. Wounds and damaged stem areas from shearing and pruning are often entry points.

Symptoms

• The disease starts in the weaker or damaged areas of plant bed and spreads to healthy plant areas. Foliage develops irregularly shaped, brown-to-tan spots surrounded by concentric rings. The spots grow in size and merge to create larger patches, as the disease progresses. Affected foliage starts dying. There are brown or black cankers or sunken areas on stems. The cankers eventually girdle and kill whole stems. Pink spores are visible within the cankers and on foliage undersides during wet or humid weather.

Management

• Maintaining vigorous plant health with regular watering and fertilizing helps discourage infection. Thinning the beds allows air circulation. Remove stressed and damaged areas most prone to disease. Pruning and removing affected plant areas minimizes the disease's spread. Avoiding overhead irrigation reduces foliage wetness. Water plants during early hours, allowing leaves to dry properly. Fungicidal control options include the use of chlorothalonil, mancozeb or thiophanate methyl.