Tom Creswell, PPDL Director
Biscogniauxia marginata is a difficult to pronounce name for a not-so-common fungus that attacks apple trees, serviceberry (Amelanchier sp.) (Figure 1), crabapple (Figure 2), mountain-ash (Sorbus sp.) and causes minor damage on a few other trees. The common name for this disease is nailhead canker, or blister canker. We had two samples of this disease in 2013. The timing is not too surprising because this fungus nearly always attacks trees that have been stressed by drought and 2012 produced one of the worst droughts in many years.
The disease gets its name from the distinctive spore producing structures formed by the fungus. These round cushions of fungal tissue do resemble nail heads (Figure 3). The canker usually runs long distances down major branches but may not kill the branch rapidly since the infection may be limited to one side. As with other fungi that infect trees and grow inside the wood, fungicide sprays provide no control. In this case management equals prevention, namely by correct watering of valuable specimen trees and shrubs during periods of drought.
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Figure 1: Nailhead canker and drought stress caused the death of this Downy Serviceberry (Amelanchier arborea).
Figure 2: Nailhead canker on crabapple
Figure 3: Distinctive fungal fruiting structures give Nailhead canker its name.
Figure 4: Cutting away the bark reveals a distinctive pattern of decay as the fungus colonizes the wood beneath.