Have you noticed the ominous black knot fungus in your yard, threatening the health of your cherished trees? Don't worry, we've got you covered.
The black death of trees, the black knot is as ghastly as it is apparent. The fungus Apiosporina morbosa causes black knot. Black knot galls are most conspicuous during the fall and winter after all the leaves have fallen. So before the first buds of spring emerge, give your cherry trees a quick scan.
Even an inexperienced gardener can quickly identify black knot by its swollen, knobby black growths. These unsightly black growths emerge along the length on branches of a range of trees common in Minnesota yards. There may be many black galls on trees infected with the black knot.
The black knot fungal disease infects prunus trees, which include ornamental, edible, and native plum and cherry trees. Many Prunus trees tolerate black knot, but others are more severely affected. In these vulnerable trees, leaves and shoots wilt and die on branches with galls.
The Lifecycle of Black Knot Fungus
During the wet periods of spring, the spores of the fungus get released. The spores are spread to other trees by the wind, where they infect young green shoots or wounded branches. The fungus grows inside the branch for many months with no visible symptoms of the disease.
As the fungus grows, it releases chemicals that make the tree grow extra plant cells that are abnormally large. In this way, the black knot is similar to cancer. This abnormal cell growth results in the swollen, woody galls on trees. What makes these galls particularly interesting are made up of both plant and fungal tissue. Black knot galls on trunks are often cracked and may ooze sticky liquid. Wood decay fungi may enter the trunk through cracks caused by black knot galls and cause wood rot.
Read Our Other Blogs
Sometimes, the branch and the gall die after spores are released in early spring. If the branch lives, the knot keeps getting bigger and produces new spores every spring. One year after infection, galls become a swollen area of the branch with a velvety olive green covering of fungal growth. Two years after infection, the gall has turned black and hard. These galls release spores in spring when wet.
The gall can completely encircle and girdle a branch. When this happens, the leaves beyond the gall wilt and die.
Treating Black Knot Fungus
To combat black knot fungus effectively, a two-fold approach is necessary: winter pruning and spring treatment. Late winter pruning, ideally in February or March when temperatures are below freezing, is crucial to prevent spore infection. Inspect your trees carefully and remove infected branches, ensuring their proper disposal through burning. This prevents the continuous release of spores that could initiate new infections within the tree.
In early spring, when flower buds are just starting to open, consider applying fungicides to protect young shoots from black knot. Since fungicides are toxic chemicals, it is advisable to seek professional assistance for their safe and effective application. Birch Tree Care specializes in the treatment of black knot fungus and offers a range of services to safeguard your trees' health.
Don't let black knot fungus cast a dark shadow over your yard — contact us today to book your spring treatment and secure a quote. Together, we can protect your trees and preserve the natural beauty of your surroundings.
