Why are trees turning black?

Q: My tree has lost its leaves. There is black stuff growing on all of the branches. What is this? Can I save the tree?

• Rodney from Youngstown

A: This disease was on a stone fruit tree, specifically a plum tree. This disease is not curable at this point. The disease is called black knot as the limbs look like black knots coming out of the branches. It affects plums and cherries for the most part.

It is fairly common. I saw several samples of this disease during 2022.

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.

Whew. That list is long. That is a lot of work!

We know it is not easy, but time spent with the home orchard is necessary work to get the production you are seeking. When you eat the plums, you know your hard work was not in vain. Just imagine what our local fruit farmers go through each year to produce quality fruit for your family.

The most important things in the list of what to do are selecting the proper site and choosing the right variety.

Several plum varieties are much less susceptible to black rot. The variety President is resistant. Early Italian, Brodshaw, Fallenburg, Methley and Milton are somewhat less susceptible than common varieties, and Shiro, Santa Rose and Formosa are much less susceptible than common varieties.

Black knot is really an ugly disease. To me, 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. Take them out of the garden area completely.

For more on the disease and pictures, please see our factsheet at http://go.osu.edu/blackknot.

Barrett is the Ohio State University Extension educator for agriculture and natural resources in Mahoning County. Visit the Plant and Pest Clinic or call the hotline at 330-533-5538 from 9 a.m. to noon Mondays and Thursdays for help with plant issues, soil testing and insect identification. For details, visit go.osu.edu/mahoningclinic.


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