Black knot on trees has woolen, solid galls on leaves, twigs, branches, roots, or trunks on the plants as signs of their presence. Though this is a sign of a common fungal disease of Prunus trees, it can cause leaves and sprouts to wither and die. If you are having a hard time with this black knot, your worries are going to be over after reading this article.
Our experts will enlighten you with the causes and remedies of the black knot.
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What Is the Common Reason for Black Knots on Trees?
The common reason for black knots on trees is a fungus called Apiosporina morbosa, which is also known as the black knot fungus. This fungus mostly attacks plum and cherry trees, regardless of whether wild or cultivated, but it also infects other kinds of fruit trees.
Apiosporina morbosa spends the Winter in the galls on branches and trunks and likes springtime to spread the disease, and by being produced by the fungus, spores start to release during the spring season’s wet period. Then the trees’ green shoots and branches get infected by the fungus carried by the wind and irregular water drops.
The fungus forms dark lumpish growths on the trunk and branches, and when galls appear, the black knot gradually cuts through the bark and destroys affected trunks. With time, they keep growing, and they wrap a side of the infected limb of the tree. Once a fruit tree is infected with the black knot, it doesn’t usually die but doesn’t produce enough fruits.
Now you know the reason for Black Knot disease. Now, let us help you with the information about the signs and symptoms of the infection and disease cycle of black knot fungus.
– Signs and Symptoms of the Black Knot
If your tree is infected with black knot fungus, you can easily identify the disease by seeing black, lumpy galls or swellings on trucks, stems, branches, and twigs that usually appear in the Spring prior to leaves coming out.
These galls are generally soft and olive green while forming elementary but get harder and black with time, and they hold more length than the width in appearance and can be long a few inches to a foot and even more. A single tree can be infected by plenty of swelling, which can cause whole branch death, not limited to the infection’s specific place.
That was the description of a visible part of the disease, but the fungus Apiosporina morbosa causes the black knot can only be seen with the help of a microscope. It would help if you looked at lean gall sections using the microscope as the fungus contains the microscopic fungal bodies and lives in the galls.
– Disease Cycle of the Black Knot Fungus
Knowing about the disease cycle is vital for recognizing the disease accurately and controlling the black knot fungus. Regarding the disease cycle, fungal spores on trees get produced on year-old or older swellings and start infections on younger, pulpy branches or injured tissue during the wet atmosphere in the spring season.
Light-complexes secondary fungi or pests gradually cover the black knots. However, pest management is not that important to solve the problem; instead, sanitation of the trees is necessary.
What Are Easy Ways to Solve Black Knot Disease on Your Trees?
Easy ways to solve black knot disease on your trees are pruning the affected branches and destroying the infected wood. As it can cause your trees to die, it’s normal to worry and look for solutions to the disease on your trees.
– Pruning the Infected Branches
It would be best to prune branches infected by the fungus and show the galls, which is a symptom of the black knot. Winter is the appropriate season to look for if your trees are infected with black knots or not, as there is a fall of leaves, and spore production gets minimal at this time.
Inspect the trees carefully, especially around branches and leaf barnacles, to check for any ruptures, bruises, cecidia, or other first signs of infection. If any symptom of the black knot is found, follow the steps we will tell you now.
Prune any knots found on the twigs, which you should do during the winter season when spore production is low. Then cut well past the canker of the branches for four to eight inches to ensure all the infections are gone, and their spores are eradicated.
Bigger twigs with established knots should be eliminated entirely by using pruning tools like a knife or chisel to kill galls on stems and mature branches, cutting down to the wood and reaching at least an inch farther from the infection.
Chopping the small infected branches is mandatory, and you will be required to trim off them below the knot no less than 15-20 cm or 6-8 inches. Please don’t make the mistake of keeping a tail end of any infected branch, as black knots can be returned because of it.
If you cannot prune infected trunks or staging branches, chop off infected tissue deeply through healthy wood no less than 1 cm or half an inch, as even after cutting, the knot-affected part of the wood will fall to the disease again if you leave a little infected tissue.
– Destroying Infected Wood
Destroying the infected wood as soon as possible is the last part of pruning the infected wood. You must exterminate them by burning, burying or taking them away from other woods which are not infected, as diseased knots are reported to produce spores for up to 4 months after they are cut but keep idly.
If you don’t terminate the wood, only compost the trees if your pile retains an inner temperature of 160 degrees to keep the infection spreading under control. Then keep scanning for and removing galls when the season progresses, and don’t let infected branches drop to the earth because the spores can survive there.
– Sterilising Cutting Tools
After trimming off the infected branches, you should sterilize the cutting tools. You can utilize a solution of 1/2 cup bleach to a gallon of water to cleanse your knives or blades by putting them in the solution for three to six minutes when you are done pruning, or you can use a commercial fungicide buying from the stores like Physan 20 or hth Algicide10.
– Preventing the Black Knot on Trees
If you are thinking about preventing the black knot fungus, then Fungicides are a great choice to fight black knot, but you have to maintain proper pruning and cleaning of the trees, and if your trees are infected already, the fungicides can little help. It is better not to use OMRI-listed fungicides as they are not good for nature.
Using neem oil, a natural fungicide, by spraying it on trees before Spring and the rainy season is very helpful in preventing leaf spots, tarnish, scrub, and different types of fungus and black knot infection spreading. Follow a 7 to 10 days cycle to apply the oil until dry weather comes.
Other fungicides, including lime sulfur and copper, also proved helpful in preventing the production of spores during the inaction period.
Apart from using fungicides, avoiding wild cherry and plum trees in your garden is an interesting way to prevent black knot disease, as the trees are prone to get black knots, and they release spores which can affect other trees in your garden. So, for precaution, you can bypass having these trees on your ground.
– Other Preventive Measures
Keep checking the trees’ health and always make sure to keep your plants healthy and stress-free, which is a great precaution to prevent the black knot. Besides, provide your trees with perfect awning ventilation, which you can ensure by trimming off the trees accurately.
Control chemical uses in your garden if you are harvesting valuable plants, and ensure enough buffer zones between harvesting and natural resources along with applying a low amount of biological control goods. If you think the problem is more severe, you can even hire a professional pruning expert.
Final note:
Black knot is caused by Apiosporina Morbosa fungus on trees, and You can diagnose the disease by identifying the black, swelling galls on the stems, trunks and branches of the trees.