Black Knot
Black Knot
Susceptible Plants- A fungus disease aptly named Black Knot afflicts backyard plum or cherry trees with grotesque hard black knots growing on twigs and branches.
The disease can be especially severe in home orchards and landscapes where gardeners may not be pruning, spraying and cleaning up fallen leaves and fruit. Black Knot also affects ornamental flowering cherries, peaches and plums, as well as wild plum and wild cherry trees. Microscopic spores produced by the fungus from early spring through early summer on one and two-year-old knots are spread by wind and splashing rain. When the spores contact young wood, they penetrate the bark either directly or through wounds and germinate. Infection generally occurs during warm wet weather, from the end of April through June. Symptoms- The first symptoms of Black Knot are small, light brown swellings on the current or last season’s growth. These swellings may be difficult to see and often go unnoticed. The disease becomes evident only after the knots enlarge and become olive-green with a velvety texture.
The knots gradually become darker and by fall they appear as hard black knots that become especially noticeable during the months when trees are bare of foliage. The knots will continue to grow until they girdle the branch and kill it. The fungus overwinters in the knots and can provide a source of new infection the next spring.
Prevention and Control - The best way to avoid Black Knot problems in the home garden orchard is to select resistant varieties of plums and cherries. Prune out and destroy (burn if possible) all diseased wood during late winter. When trees are not wet, carefully prune out infected branches. Gardeners should make cuts 4in(9mm) below the knot and dip pruning shears in rubbing alcohol to disinfect them after each cut. Do not allow the prunings to fall and remain on the ground where they will remain a source of infection. Destroy all clippings or bury them in the ground. . Fungicidal spray- for persistent infections causing black knot use Sulfur Fungicide, Lime Sulfur Fungicide or Bordeaux Mixture as directed..
|
|
