Hello. It has been determined by my local arborist my crabapple has black rot. Since the tree is overall in good condition, we have trimmed out the impact branches and would like to treat the tree so the infection does not spread. Please advise what to use to prevent the spread and when and how often it should be applied. Thank you
Oakland County Michigan
Removing and destroying all dead wood during annual pruning is a highly recommended control measure. Also remove any mummified fruit on the ground or in the tree. Because Botryosphaeria is a canker-producing fungus, you should follow good horticultural practices to improve tree health as you would with any canker disease. This means removing dead wood, watering the tree in periods of drought that last two weeks, and fertilizing in the fall or early spring.
For management of fruit rots, fungicides may be used as preventatives. Once infection occurs, there is no cure. Fungicides are not effective in managing black rot cankers; cultural practices listed above are important for management of cankers and reduction of inoculum.
I hope this helps. Thank you for your question.