Nectria canker—Nectria spp.
Many woody species are susceptible to coral spot fungus (Nectria cinnabarina), European canker (N. galligena), and other Nectria spp. Cankered limbs are more susceptible to breakage and may be hazardous.
Identification
Nectria spp. infection of branches and twigs causes leaves and shoots to wilt, often beginning in spring. Infected branches and twigs may die back and cankers (discolored, sunken, often elliptical areas) commonly develop in woody parts.
Nectria spp. infection is often overlooked until clusters of the fungal fruiting bodies erupt from bark, usually during spring and summer. Each of these spherical orange or red sporodochia and perithecia (the coral spots) are about 1/50 to 1/16 inch in diameter and later turn pale or become covered with white spores.
Where these fungal growths occur, cutting away bark reveals a margin separating dead (dark brown, necrotic) and healthy (cream-colored) wood. The green, living cambial layer found just beneath healthy bark is absent where cankers occur.
There are many other common causes of cankers, including other species of canker fungi.
Life cycle
Nectria fungi infect woody species through weakened or wounded tissue, such as leaf scars and pruning wounds. Plants are especially susceptible to infection when unhealthy or stressed, such as from recent planting.
Plants infected when young may die, but Nectria spp. rarely, if ever, kill older plants. Callous tissue developing around wounds often limits canker spread and prevents girdling of the trunk or limbs.
Solutions
Proper cultural care and good growing conditions are the most important management methods. Plant only species well adapted to local conditions and especially provide appropriate irrigation. Avoid wounding or pruning plants, especially if they are growing poorly. Unless pruning must be seasonally timed to avoid other problems, prune if needed during early summer to reduce the likelihood of Nectria infections.
No fungicides cure Nectria infections. If plants are heavily infected or susceptible species are newly planted, the frequency of new infections may be reduced by thoroughly spraying a fixed copper or a freshly prepared Bordeaux mixture during early leaf drop, just before the rainy weather. If leaf fall is prolonged by warm fall weather, a second application may be warranted when three-fourths of leaves have dropped.
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European, or Nectria, canker on apple
Red fruiting bodies of Nectria galligena
Brown, canker margin beneath bark
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