See:
Alder (Alnus spp.) - Collar Rot (Phytophthora Canker)
Cause The fungus Neonectria major occurs on both Alnus rubra (red alder) and Alnus incana. In southwest Washington perithecia began to develop through early spring and have been observed to contain mature asci by late spring and early summer. Ascospores release when the perithecia begin to dry following rain or high relative humidity. Spores may gain entry through natural opening such as leaf scars cracks at junctions of twigs and branches, senescence of lower branches, or lenticels. Spores may also infect wounds and injuries caused by winter cold, drought, sunscald, hail damage or insect feeding. Weakened or stressed trees from drought are more susceptible. Stands that receive an average of 10 inches or less of average fall precipitation should be closely monitored for infection. Perithecia have also been found on downed trees, thinning slash, and branches. May be confused with Collar Rot (Phytophthora Canker).
Symptoms Cankers begin as small, dark spots on the bark that secrete a dark exudate. During the second year, spots enlarge and begin to affect the cambial region with cracks appearing in the bark. Typically, the sunken area in the center also cracks, often in the shape of a cat's eye. In severe cases, these cankers resulted in tree death. Dark red perithecia can be found growing near the center of cankers.
Cultural control
- Pre-commercial thinning of stands just prior to uniform crown recession. Thinning during the winter or early spring may help reduce inoculum.
- Keep trees in good vigor and avoid wounding.
- Prune lower branches before crown recession and remove thinning slash.
- Remove and destroy dead or severely cankered branches or trees.
Reference Cootsona, C. 2006. Identification and distribution of Neonectria major causing cankers on red alder (Alnus rubra). MS Thesis, University of Washington.