How to Cure Black Knot Fungus on Fruit Trees


It’s a disease that gardeners or orchard owners typically fear. The disease known as black knot, which is caused by the fungus Apiosporina morbosa, may affect many different kinds of trees, including those that provide fruit. If it is not controlled, it may cause the tree to become stunted or possibly die. {{!! -!! The black knot fungus is responsible for an unimaginable amount of damage that has been sustained by trees throughout North America. In addition to taking the lives of cherished trees in people’s yards, it poses a significant threat to the financial security of those whose livelihoods depend on the cultivation of fruit trees. You may, however, simply cure your tree if you follow some straightforward advice, but you should do it as soon as possible. {{!! -!! The black knot fungus, a frequent kind of blight that may affect fruit trees, can spread both sexually and asexually. It begins by infecting the twigs and branches of a tree while it is in its early stages. At first glance, the condition appears to be small olive-green bumps, similar to those that can be found on the growing points of succulents, or fruit spurs. From this point on, it begins to expand, and after two or three years, it develops into a tough black “knot” that may reach a length of six inches, despite the fact that it can spread beyond the branch by several inches. {{!! -!! The infection will develop spores that will cause it to spread to other parts of the branch, and in time, it will cause the branch to die. It will develop on the interior as well as the exterior of the tree, which might ultimately lead to its demise. Insects will also start filling in the older, longer black knots that have been there longer. The infection is not only detrimental to the plant’s health, but it is also extremely unsightly, and it can lessen any aesthetic value that a tree may have. {{!! -!! The spores that are produced by the knots are carried to neighbouring twigs by the wind and the rain. The ailment is at its most acute when the weather is warm and moist, although the first swellings may not show up for many months, most often in the spring. Knots that are located in close proximity to one another have a greater chance of fusing together, becoming bigger, and being colonised by a distinct fungus called Trichothecium roseum, which gives the knots a pinkish-yellow tint. {{!! -!! Pruning the affected branches is the most effective method for dealing with the plum tree blight, which also affects a wide variety of other tree species. When it is not possible to notice the knots on the branches due to the absence of leaves, which occurs in the late autumn, winter, or early spring, pruning should be performed. It is advisable to prune the branches starting six to eight inches below the knot, or ideally, all the way up to a healthy collar. Make sure the pruning blades are sharp, free of debris, and disinfected with either Pine-Sol or isopropyl alcohol. {{!! -!! The trunk of a tree may potentially get infected with black knot disease. Large portions of the bark will change appearance, becoming tough, dark, and swollen. The galls that were on the trunk would eventually split and leak a sticky substance. {{!! -!! If the black knot infection were to progress to the trunk itself, the diseased wood and tissue would need to be removed to a distance of at least half an inch beyond the illness’s border. Because diseased wood may continue to transmit spores for many months after it has been removed, the wood should be burnt or buried as soon as possible. Chemical therapies are not indicated for those suffering from this illness. {{!! -!! Despite the fact that Apiosporina morbosa may infect a wide variety of plant families, it is most often found in trees and shrubs belonging to the prunus genus. This genus has more than 400 different species of flowering plants that are members of the rose family. Many of these shrubs and trees are either very important to the economy or are cultivated specifically for their aesthetic value. {{!! -!! It is a common plum tree fungus (Prunus subg. Prunus) that can infect trees in USDA growing zones 3 through 8, but it can also infect almond (Prunus dulcis) trees in zones 5 through 9, peach (Prunus persica) trees in zones 4 through 8, apricot (Prunus armeniaca) trees in zones 5 through 8, and cherry (Prunus avium) trees in zones 5 through 7.

Black knot fungus has caused untold amounts of damage to trees around North America. Besides killing beloved backyard trees, it can seriously harm the livelihood of people who grow fruit trees. However, by using some simple tips, you can easily treat your tree, but you must treat it quickly.

Identifying Black Knot Fungus on Trees

A common fruit tree blight, black knot fungus spreads both sexually and asexually. In its earliest stages, it infects the twigs and branches of a tree. At first, the ailment looks like the small, olive-green bumps on a succulent’s growing points or like fruit spurs. From here, it swells, and after two or three years, it matures to become a hard black “knot” that can reach 6 inches in length, though it can extend past the branch by several inches.

The infection will produce spores that spread it, and eventually, it will kill the branch. It will grow both on the inside and outside of the tree, potentially killing it. Insects will also begin filling the older, long black knots. Besides being harmful to the plant, the infection is thoroughly ugly, and it can decrease any aesthetic value a tree has.

The spores created by the knots are spread by wind and rain to other twigs. It’s most severe during mild and wet conditions, and the earliest swellings may not appear for several months, often in the spring. Sometimes, knots that are close together can fuse and become larger, and a different fungus (Trichothecium roseum) will also invade, covering the knots with a pinkish-yellow hue.

Dealing With Apiosporina Morbosa

The best way to deal with this plum tree blight, which also affects many other trees, is to prune the infected branches. Pruning should be done in the late fall, winter or early spring when the knots are both easy to see (from lack of foliage) and dormant. It’s best to remove the branches from 6 to 8 inches below the knot or, ideally, to a healthy collar. Ensure pruning blades are sharp, clean and disinfected with isopropyl alcohol or Pine-Sol.

Black knot can also infect the trunk of a tree. Large areas of bark will become rough, black and swollen. The galls on the trunk will crack and ooze a sticky liquid.

Should the black knot infection spread to the trunk itself, remove the diseased wood and tissue to at least ½ inch beyond the edge of the infection. Diseased wood can still spread spores for months after removal, so it should be burned or buried immediately. Chemical treatments are not recommended for this disease.

Which Fruit Trees Will Black Knot Fungus Infect?

Though Apiosporina morbosa can infect many species, it’s quite common in trees and shrubs in the prunus genus, which represents more than 400 species of flowering plants in the rose family. Many of these trees and shrubs are of great economic importance or grown as ornamentals.

It’s a common plum tree fungus (Prunus subg. Prunus); USDA growing zones 3 through 8, but it can also infect almond (Prunus dulcis); zones 5 through 9, peach (Prunus persica); zones 4 through 8, apricot (Prunus armeniaca); zones 5 through 8; and cherry (Prunus avium); zones 5 through 7 trees.