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Black Knot - Apiosporina morbosa
  Helen Atthowe, Missoula County Extension Robert L. Anderson, USDA Forest Service, www.ipmimages.org  HOSTS: Chokecherry,
plums, cherries, and other trees and shrubs in the genus Prunus. DESCRIPTION:
The
fungus forms long, irregularly-shaped, black galls along branches and
twigs and rough, black, sunken cankers on stems. LIFE
CYCLE: Wind and
rain-disseminated spores infect new growth in the spring when
>6 hours of rain occurs at temperatures between 55-77° F. The
spores enter through green shoots of the host plant. Galls are seen mid
to late summer when the fungal hormones cause swelling. The following
spring after infection, the fungus produces fruiting bodies. Once
established, cankers and galls are perennial and will spread along the
limbs. The fungus may spread systemically through the xylem and phloem
to produce cankers on other limbs and the trunk. CONTROLS:Cultural: Prune out black galls in late summer and fall on a hot, dry day. Keep water off leaves, branches, and trunks. Chemical: Protect new growth with oil-free lime sulfur sprayed when buds start to break in the spring. When weather is wet and warm (> 60° F.), protect new growth with sulfur. Only effective if galls have been pruned out. |
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