Sunday, November 2, 2008

Black Knot Fungus

Black knot fungus  
The disease black knot is caused by the fungus  (Apiosporina morbosa) . Black knot can occur on both sweet and sour cherry,  wild cherries and plum trees.This is a black lumpy fungus that feeds on the branches, eventually disfiguring the tree.
     The Black knot fungus infects trees between April and June during warm, wet weather. The first symptom is a small, light brown swelling on the current or last year’s growth. These swellings are difficult to notice at first until the following spring when they enlarge and appear as an olive green velvety knot. During this stage the fungus produces spores which are released at or near the time the trees are beginning to leaf. Spore release is heaviest at blossom time. Soon after, the knots become darker and by fall, they appear as the black knots that are atypical of the symptoms. The disease may not be recognized until one or two years after the original infection. Knots will continue to grow until they girdle the branch and kill it. Severe infections can eventually kill the tree.

     Examine your trees yearly for the presence of Black knot. Remove all infected branches from any diseased trees adjacent to the property if possible. Prune out and destroy infected branches before bud break. Prune at least 2-4 inches below each knot because the fungus grows beyond the edge of the knot itself. If pruning or removal of major limbs is not possible then you must cut away the knot down to healthy wood at least 1/2 inch beyond the knot. Infected trees usually require pruning on an annual basis until the disease is completely eradicated.
  1. Avoid planting new plums, prunes or cherries next to or downwind from areas with a significant black knot problem.
  2. Fungicides may offer protection against Black knot, but are likely to be ineffective if pruning and sanitation are ignored. These treatments are generally not recommended in urban ares
Source: My Garden Patch

Many pieces of fungus, -- approx. 10 were cut from the tree.
A large knot of fungus

Martin removing some branches.

Showing a large piece of black fungus.

He has a long tool to do the job...

the same tree in the Spring in flower

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