The Richmond Register

Lifestyles & Community

February 19, 2013

Be sure to check fruit, almond tree branches for black knot fungus

RICHMOND — Are you growing, plums, cherries, peaches, apricots or almonds?

If you are, then be sure to check the branches of your trees for a thick, black, irregular looking growth on the stem.

This growth has probably been there for quite a while, but went unnoticed because of the presence of leaves.

Unfortunately, what may be growing on your tree is called black knot. It is a fungus that disrupts the normal growth of twigs.

Infection may have occurred over a year before the characteristic tumor develops. Often, the tree has been infected for two years when the problem is finally noticed. It is especially common on plums.

The disease overwinters in the knots on the tree. Once the tree begins to bud out in the spring, the fungal spores are released during warm, wet weather. New green shoots and wounds on the tree are the most susceptible to this infection.

These knots continue to grow slowly and may appear as small galls by the end of the first summer. These small young galls appear as olive green with a velvety surface. By the second summer, the gall changes into a hard, coal-black structure. Once the tree is infected, the fungus can spread to other parts of the tree and new galls will form. Knots will continue to expand until they girdle the branch and it dies.

So, what can you do? The best thing is to check on your trees. If you don’t, you may be surprised to find something that has been going on for quite a while. When the leaves are off the tree in the winter, be sure to check them for anything out of the ordinary. If you find the growth, prune it out. Cut the stem at least six to eight inches below the knot. Discard and destroy all the effected wood. Fungicides are recommended only for sites with valuable trees or with severe infections.

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