What is Black Knot Disease?

Black Knot Disease on Tree

Black knot disease is a serious fungal disease that can hurt fruit trees by killing new growth and disfiguring the tree. Commonly affecting plum trees and cherry trees, this disease can devastate your trees and ruin your orchard. It spreads quickly and can overtake an orchard in no time. If you have fruit trees on your property, you need to be aware of the way this disease could affect your trees, what you can do if you notice signs of it, and be aware that tree disease and tree fungus treatment from a tree care expert such as Safari Tree may be necessary.

What Is Black Knot Fungus?

Black knot fungus is caused by the Apiosporina morbosa fungus. It causes knobby dark growths on the tree’s trucks or branches. While mature trees can handle the fungus, those with weak branches or the trees that are younger cannot, and the disease can lead to tree death.

Black knot fungus is also dangerous because of how quickly it can spread. During the winter, it remains dormant in the tree, so it appears that the fungus has gone away. Then in the spring, rain allows the fungus to release spores, which can spread on the wind. These spores take hold on different trees, spreading the disease throughout the orchard. This chronic problem will continue to spread year after year, so you need to deal with it decisively.

Black Knot Disease

What Are the Symptoms of Black Knot?

The most obvious symptom of black knot disease is a large gnarled black swelling, which is called a gall. However, if you can spot earlier signs before the large black gall develops, you can start treatment more easily.

At the start of the disease, the tree will develop small olive-green swellings. Over the next two to three years, these will grow and turn black. The final gall will grow to be four to six inches in size. Once the gall matures, it start producing spores which spread to other trees. Eventually, the gall will grow large enough to completely surround the branch, killing the leaves beyond the point of the gall.

How to Get Rid of Black Knot

Black knot can be a challenging disease to treat. One of the first steps to take when you notice the problem is to prune the tree. Identify and remove all the branches that have obvious black knot towards the end of the winter. Aim to prune four inches below the fungal growth, just in case the disease has spread but is not yet visible. After pruning the tree, disinfect the pruning tools so you do not inadvertently spread the disease to a healthy tree. Remember that the pruned branches can spread the disease, so dispose of them properly.

After removing the galls, apply fungicides, especially in younger trees. Fungicide is most effective if applied after the flower has budded, but before it is in full bloom. Choose a fungicide that is designed for your region for the most effectiveness.

This job is not an easy one to tackle. You must be able to identify all of the infected branches of the tree, and remove them effectively, or the tree will simply develop a new infection. The best way to deal with black knot is to hire a certified arborist who can identify the black knot fungus and treat the trees as effectively as possible.

If your cherry trees, plum trees or other fruit trees are showing signs of black knot disease, get help right away. Regular checkups from a Safari Tree arborist will help identify black knot fungus before it gets out of hand.