Volutella stem and leaf blight is a common boxwood disease in landscapes and nurseries. The disease caused by the fungal pathogen Pseudonectria buxi can be devastating in the landscape and may cause significant losses in the nurseries. Volutella stem and leaf blight affects several species of boxwood. Plants subjected to stress factors such as winter injury, exposure to bright sunlight, scale insects, and stem wounds are at a greater risk of infection.
Pseudonectria buxi overwinters in boxwood branches, leaves and plant debris and causes infection under favorable weather conditions (68°F to 77°F and relative humidity > 85%). Visible symptoms begin to appear in the spring as delayed growth or poor vigor. Leaves of affected branches initially are light green to red, later turning straw or tan with eventual death of the entire infected branch (Figure 1). Dead leaves turn upward and remain attached to the branches. Young leaves are more susceptible to infection than mature leaves. Symptoms on stems appear as a sunken lesions with stem girdling that results in dieback. At a later stage of infection, plants may start losing bark and show discoloration around the infected area. During wet events, the fungus produces sticky orange colored spore masses (sporodochia) that can be viewed using a hand lens on the lower surface of infected leaves and stems (Figure 2). This characteristic distinguishes Volutella blight from winter injury and other more devastating diseases such as Boxwood blight (Figure 3). The pathogen is primarily spread through irrigation, rain splash and contaminated tools with long distance spread in movement of infected plants and cuttings.
Pseudonectria buxi, an opportunistic pathogen, is mostly associated with stressed plants. Thus cultural and sanitation practices that promote plant vigor and reduce plant stress during the season are important for disease management. Prune out diseased branches several inches below the transition zone (area between the healthy and the dead tissue) in dry weather. Rake and remove fallen leaves of infected plant materials to avoid spreading the spores. Dig out and destroy severely infected plants. Thin plants on existing beds to improve air circulation and light penetration. Make sure to sanitize pruning tools after working with each plant. Volutella blight does little damage to healthy and vigorous plants, so establish new plants in a well-drained soil and do not over crowd plants. Provide proper nutrition based on soil test results and water adequately. Avoid overhead irrigation for both newly planted and existing beds. Though varying in effectiveness, fungicides such as chlorothalonil, copper and mancozeb can be applied preventatively before new growth emerges in the spring and continued every 7 to 10 days until new growth is completed. Thorough spray coverage of the branches is required for effective disease control with fungicide.
Volutella stem and leaf blight could be confused with other boxwood diseases and winter injury. For accurate diagnosis submit sample to the MU Plant Diagnostic Clinic. For further information on sample collection, packaging and shipping, visit the MU Plant Diagnostic Clinic website http://plantclinic.missouri.edu/
For further information on boxwood blight, Purdue University has a comprehensive description and management of the disease. https://www.extension.purdue.edu/extmedia/bp/bp-203-w.pdf
REVISED: February 21, 2017