Prune trees to avoid black knot

Q. My tree is losing its leaves and it has black stuff growing on the branches.

I know it’s probably a disease, but what can I do about it?

Carl from Canfield

A. This disease was on a stone fruit tree from Carl’s backyard orchard. It is a serious disease called black knot. It affects plums and cherries for the most part. It is fairly common. I have seen several samples of it already this year.

The solution is easy. Use proper plant spacing; choose resistant varieties; employ proper pruning practices to allow airflow to dry leaves quickly and sunlight penetration into the canopy; clean up all leaves/branches from the ground at the end of the season; and consider a spray program (organic or conventional) to reduce fungal pathogens.

Yes, I know that does not sound easy.

But a backyard orchard is hard work. Just imagine what our local fruit farmers go through each year to produce quality fruit for your family.

Black knot is really an ugly disease. It looks like black foam is growing out of the branches on the tree. When this disease is found, the infections should be pruned out 2 to 4 inches below the infection (toward the trunk). Destroy these infected branches.

The best method for avoiding this disease is to plant in the backyard orchard. Again, pick resistant varieties. Clean up any tree debris after leaves fall in autumn. Prune, prune, prune. I always say a fruit tree is not beautiful until you see the ripe fruit ready to pick.

For more on the disease and pictures, see our factsheet at:

Eric Barrett is the Ohio State University Extension Educator for Agriculture and Natural Resources in Mahoning County. Call the hotline at the office on Mondays and Thursdays from 9 a.m. to noon to submit your questions at 330-533-5538.

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