|Black Knot on Prunus.|
As a general rule of thumb gardeners are told to prune out any diseased branches from trees and shrubs before the end of March. The biology behind this rule tells us that during cold winter weather, trees and the microorganisms that cause tree diseases are dormant. When the weather warms up, trees become active and so do their pathogens. Pruning cuts made in cold weather are less likely to become infected with the pathogen being pruned out or any other pathogen.
|Fire blight canker on crabapple|
|Golden Canker on Pagoda Dogwood|