Recent pathogens of interest seen in the UMass Extension Plant Diagnostic Lab:
Verticillium wilt of Japanese maple (Acer palmatum). Three trees, approximately 5–6′ tall were planted in a small, urban backyard in July of 2014. Site has full sun and trees were irrigated as needed. During the spring of 2015, one tree began showing symptoms of canopy dieback. A second tree became symptomatic in autumn of last year and the third tree became symptomatic in early 2016. Browning foliage, premature leaf shedding, blackening of canopy shoots and branches were all observed. Upon incubation, numerous microsclerotia were produced from the blighted shoots. Verticillium produces these black, seed-like structures to survive in dead plant material and in the soil, where it can persist for multiple years.
Infestation of the azalea bark scale (Eriococcus azaleae) on azalea (Rhododendron ‘Delaware Valley White’). Stems were brittle and blackened with sooty mold fungi. This black color contrasted sharply with the white-colored scales that were adhered to the bark, primarily in stem crotches. When populations are high, this insect pest can cause considerable damage by feeding on the stems and undersides of young foliage.
Stem cankering caused by Phomopsis and needle spots caused by Phyllosticta on eastern hemlock (Tsuga canadensis). Tree is nine-years-old and has been present at the site for five years. One of several hemlocks at the site growing in a shaded setting. Adjacent hemlocks are healthy and free of dieback symptoms. Phomopsis is common on eastern hemlock, causing a shoot tip blight after predisposing stresses have weakened defenses. Needle spots were singular, yellow in color and mostly confined to the needle margins. While Phyllosticta is common on Thuja and occasionally found on Abies, it is not a common pathogen on Tsuga.
Branch and trunk cankering caused by Botryosphaeria and Fusarium on sweetgum (Liquidambar styraciflua). Ten trees, 14-years-old and present at the site for ~10 years, growing on a slope between a parking lot and a river. Visible cankers with callus tissue and thick sap were visible on the submitted sample. In some cases, sweetgum sap is so thick and voluminous over the wound it prohibits pathogen identification. One tree was removed while others exhibit branch dieback and general decline.
For more detailed management information for woody plant diseases in the landscape, refer to UMass Extension's Professional Management Guide for Diseases of Trees and Shrubs.
Report by Nick Brazee, Plant Pathologist, UMass Extension Plant Diagnostic Lab, UMass Amherst.