When the tree is growing, it walls off the fungus. If your trees have dropped the majority of their leaves before September, for several years in a row, fungicides can be used to protect leaves. Rake up and compost fallen cherry leaves in September or October. Learn in depth the characteristics of these cherry tree diseases and pests and the authorized treatments for their control. Black Knot Tree Disease Info. The fungus survives the winter in fallen leaves. Apply at the right time the treatments against the diseases of the cherry tree.It is essential to obtain cherries of the highest quality. Such pathogens can harm an entire orchard of cherry trees, putting a full halt to any charming blossoms or juicy fruit. When tree growth slows or stops, the fungus continues invading. It also does not look like Black Knot from the pictures I have seen. Cherry tree enthusiasts look forward to it each spring: a mass explosion of light pink blossoms. I discovered a white fungus covering some of the trunk and branches of my Weeping Cherry. Black knot fungus (Apiosporina morbosa) is primarily a disease of plum and cherry trees, although it can also infest other stone fruit, such as apricots and peaches, as well as ornamental Prunus species. On rainy days, the fungus releases spores which are carried on wind currents. Black knot disease spreads in spring. Prune cankered limbs and promote tree vigor. The cherry tree is delicate and can be affected by different pests and diseases. Removing these leaves will reduce disease spores the next spring. What’s not so exciting for lovers of the blossoms and their sweet fruit is the threat of cherry tree diseases. Trees with freeze damage and those under drought stress are most susceptible. At this point itÂs hard to tell if branches are dying because most all of the leaves are off because of the season. Leucostoma cincta or L. persoonii (formerly Cytospora) Infection can occur at any time of the year. Fungicides.