The conidia can remain viable for at least one year. Leaf infection usually occurs during the petal-fall period. Conidia become attached to the leaf and may germinate in a film of moisture within 5 or 6 hours. After germination, the fungus penetrates the leaf through natural openings in the under surface or through insect, hail or other wounds. Control Control of black rot is best achieved through an integrated program of cultural practices and chemical control measures.
Sanitation is critical for effective control.
Piles of prunings are an important source of inoculum and should be removed from the perimeter of the orchard or burned. Prunings can be left on the orchard floor if they are chopped with a flail mower, which removes much of the bark and allows them to decompose faster. Removal of mummified apples and pruning out dead wood in the tree are important for reducing the inoculum within the tree. Pruning out current-season shoots infected with fire blight is also important, because they can be colonized and serve as an inoculum source during the same growing season. Any practice that helps to maintain trees in a healthy vigorous condition is critical for controlling the canker phase of the disease.