What is one of the first signs of black knot on a tree?

The formation of gnarled branches is indeed one of the first signs of black knot disease in trees, specifically affecting species like cherry and plum. This disease is caused by the fungus Apiosporina mooreana, which invades young tissue and results in characteristic swelling or knots on the branches. Initially, small, dark, and warty galls develop, leading to noticeable distortion and gnarled growth patterns, which can ultimately severely affect the overall health of the tree.

Recognizing these gnarled branches early is crucial for effective management of the disease, as it allows for prompt intervention, such as pruning out infected wood before the fungus has a chance to spread. Other options, such as dropping leaves or healthy foliage, are not indicative of the early disease manifestation. Bright flowers will not appear until the tree has overcome initial infection stages, making them irrelevant to identifying the onset of black knot.