Gibson Priest

Gibson Priest

What causes large black galls to form on the branches of my plum trees?

Black knot is a fungus disease that attacks several types of fruit trees, especially plum, peach and cherry. Overwintering disease spores infect branches in the spring, and later in the year, large black, corky galls develop on the limbs.

The galls slowly enlarge, cutting off water and nutrients to the branches causing stunting, wilting and dieback of the branches. Prune out and destroy all infected branches, cutting 4 to 6 inches below infected tissue.

Why did my peaches turn brown and rot this summer?

Brown rot is a common fungus disease that infects the twigs and fruit of peach trees. Twig infection results in the development of cankers on the branches and stems and petal blight on the flowers.

Canker and blight in turn produce spores that infect the fruit. The fruit initially has a brown spot which expands to rot the entire fruit into a “mummy”. These mummies cling to the tree or fall to the ground and allow the fungus to overwinter.

For disease control it is critical to remove mummies and infected twigs as soon as they appear. Also, good insect control is particularly important as unblemished green fruit is not as susceptible to disease infection. The fungus needs a wound to enter these fruits.

Pruning the trees annually also aids in spray coverage, air circulation and good disease control. For severe infections, treat peach trees with a recommended home orchard spray product.

If you have any questions regarding fruit trees or other gardening topics, you are welcome to contact the extension office at 770-749-2142 or email

For more information and details on upcoming events, check out the Polk County Extension office on Facebook by searching “UGA Extension Polk County.”

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