Black knot or black fungus is a common tree disease and it’s caused by a fungus Apiosporina Morbosa. It mostly affects fruit trees like cherry and plum trees, both cultivated and wild. It manifests by creating and developing knobby dark or black growths on the branches and trunk. If left untreated, a black knot can result in the death of a tree. 

The Nature of Black Knot in Trees

black knot on tree in woods

This tree disease spreads during spring, as that’s the time of the year when it rains the most. It’s a perfect season for the fungus to release spores. The wind carries the spores and helps them find their way to the unhealthy branches and newer growths.

While outbreaks are most common for wild trees, they can spread to your yard if you don’t maintain your trees and your property. The trees that are most susceptible to black knot are weaker and younger trees, while healthy, big, and older trees are able to resist it.

The Symptoms of Black Knot

You don’t need to be a tree expert to spot the symptoms of black knot. To those unaware of this fungus, black knot will mostly look like some sort of mushroom. While mushrooms are quite common on trees and they mostly don’t damage the tree, the black knot is the exact opposite.

With that in mind, you can tell a black knot from a mushroom due to one of its most distinctive features: a gnarled black swelling, known as a gall. It’s small and green in the beginning and it develops more and more as the infection takes hold. It grows in size over time, becoming harder and turning black.

Once it’s fully matured, it will start producing more spores and thus, continue spreading the infection. It also grows on the inside of the tree, killing the twigs and leaves around it. The more it grows, the more the infection spreads, eventually killing off the entire tree.

How to Prevent and Treat Black Knot

house with trees and yardSince black knot has those distinctive black swellings, it’s quite easy to diagnose. It’s even more noticeable during cold months when the trees are naked. To prevent black knot, the best thing to do is pruning. Late winter is the best time to do it.

Remove all twigs and branches with black swellings. After you prune, disinfect and clean your cutting tools, to make sure you don’t spread the infection with the next pruning. Infected branches are still capable of infecting the trees around them, so make sure you dispose of them properly.

If black knot still manages to infect your trees, the best way to treat it is by using fungicides. These products are extremely effective at protecting younger trees. Before you apply fungicides, remove any existing black swellings, as this will help protect the newer trees.

If the problem persists, contact us today so that we can take care of the infection for you, as this is better than losing the trees on your property.