During the spring, many homeowners notice changes or problems arising in their gardens and landscapes. Throughout May, the Plant Diagnostic Lab received many samples and emails of evergreen plants such as junipers, arborvitae, cedars, and boxwoods for diagnosis. Phomopsis Tip Blight on conifers and Volutella Blight on boxwood are two common diseases seen this time of year. Homeowners tend to notice symptoms in the spring and early summer when conditions are wet and damp and conducive for disease development.
Phomopsis blight is caused by the fungal pathogen Phomopsis juniperovora. Plants that are commonly affected include juniper, cedar, cypress, and arborvitae. Most infections occur in April through early June and in the fall but can occur throughout the growing season on young foliage during wet and humid conditions. Symptoms first appear on immature tissues about 3-5 days after infection. Older, mature branches are resistant. After infection, small yellow spots can be seen on the foliage. Eventually, shoot tips will turn a reddish, brown color after the fungus has entered the xylem.
Infected branch tips on juniper. Bruce Watt UMaine. bugwood.org.
Over time, cankers will form at the base of the blighted shoots, appearing as a gray band. These cankers can girdle stems less than 1 cm in diameter. Black pycnidia, or tiny fruiting structures, form on killed tissue 3-4 weeks after infection. During wet weather, yellowish conidia, or spores, are extruded from the pycnidia and spread by wind and rain splash. The pathogen can remain on the host and continue to spread spores for up to 2 years when environmental conditions are favorable.
Volutella blight on boxwood hosts is caused by the fungal pathogen Pseudonectria buxi. Symptoms begin in spring as poor vigor and leaves turning light green to straw or tan colored. Leaves turn upwards and tend to remain attached to the branch. This key observation can help distinguish Volutella from boxwood blight, which causes rapid defoliation. Additionally, distinctive black stem streaking and cankers are signs of boxwood blight. Volutella can cause sunken lesions on the stems and plants may eventually lose bark.
Volutella blight symptoms. Photo by Lillian Borbas, UConn 2021
Straw-colored leaves attached to branches. Sunken stem lesions. Photo by Lilian Borbas, UConn 2021
Black stem streaking on a boxwood diagnosed with Boxwood Blight. Mary Ann Hansen. VPI & State University. Bugwood.org
On the undersides of leaves, Volutella will form distinctive orange to salmon-colored sporodochia (fruiting bodies) in moist and humid conditions. The pathogen is spread through rain splash or contaminated tools and is commonly associated with plants that are stressed. Maintaining plant vigor and utilizing the cultural controls outlined below can help manage this disease.
Sporodochia on boxwood leaf. Bruce Watt, UMaine. Bugwood.org.
Management recommendations
For both Volutella and Phomopsis blight, control options are similar. When growing plants susceptible to these diseases, preventative methods, proper planting practices, and cultural controls are important for management. Proper site selection can discourage infection, for example, well drained sites with proper light exposure and air circulation. Ensuring that plants are properly spaced will reduce humidity and moisture around the foliage. Make sure the plant’s mature size is considered when planting. Properly irrigate and fertilize based on the needs of the plant and planting site. Do not water with sprinklers or overhead irrigation as this will encourage prolonged leaf wetness. Avoid letting weeds or other vegetation grow close to the plants. Excessive watering or fertilizing can make the plants more susceptible to infection. Avoid shearing, wounding, or pruning plants in wet, humid weather as this will aid in disease spread.
Regularly check your plants for signs of the symptoms described. If these symptoms are observed, cultural practices should be implemented first. Remove all infected tissue during dry weather, cutting 3-4 inches back from the damage. Disinfect tools between plants and cuts with 10% bleach or 70% isopropyl alcohol. Discard or burn the infected branches as they can be a source of disease. If the plant is heavily infected, it may need to be removed. Consider choosing plants that are more resistant or not susceptible to the disease.
Fungicides may need to be applied if infections become severe and these cultural controls are exhausted. However, many fungicides are used preventatively and should only be used after cultural controls have been tried. They are often only effective if followed by this management and applied before new growth begins in the spring. Whenever using fungicides, always read and follow the label for information on proper rates and application times.
Lillian Borbas
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