The flowering crabapple is a drought tolerant, low maintenance tree that can reach heights up to 25 feet. It produces showy spring blossoms that are followed by showy displays of fruit in the summer months. Its fall leaves range from yellows to purples with twigs that range from greens to reds. Although the tree is drought and cold tolerant, the crabapple is susceptible to several diseases. These diseases should be controlled as quickly as possible to prevent permanent injury.
Fire blight is a bacterial disease that can destroy the entire crabapple tree. The bacterial develops during the winter months and lies dormant in defoliated debris, mummified fruit and trunk cankers. Crabapples that have been infected with fire blight will experience wilting and deadened blossoms and foliage, rotted apples and bacterial ooze from the tree. Severely infected trees will also display weakened and deadened twigs and branches, infected water sprouts and discoloration o shoot tips. The disease can be controlled with pruning and cooper-spray treatments. Infected areas should be pruned away with sterile shears that are sterilized between each cut.
Powdery mildew is a fungal disease that lies dormant in and infects the crabapple’s terminal buds. Infected buds will have delayed blooms, much later than those that are not infected. The crabapple tree will also display the development of powdery mildew patches on the underside of infected foliage. The foliage becomes brittle and wilted as the disease progresses. Crabapple blooms will turn brown, shrivel and die. Infected fruit will develop vascular, diseased lines and will shrivel. Fungicidal treatments are effective in the controlling powdery mildew. Proper control may require a series of seasonal application for optimum effectiveness. These requirements vary by crabapple species, planting location and disease severity. Speak with a local horticultural specialist for treatment assistance.
Apple scab is a fungal disease that is commonly found in cool, moist planting locations. This fungal disease infects the foliage and fruit of the tree. Infected foliage will develop black circular spots with a velvety fungal covering on its underside. The fruit and twigs of the crabapple tree will develop lesions and scabs. These disfigurements begin as blackish lesions that become sunken with tannish or yellow-colored halos. Severely infected foliage and fruit will die and drop from the tree. The canopy area of the crabapple tree should be kept free of debris to reduce the potential of infection. Diseased areas should be removed from the tree as early as possible. The pruning shears should be sterilized before beginning and in between in pruning cut. Fungicidal sprays can used to prevent the onset of the disease. These sprays should be used only after long periods of rain and humidity. Cooper sprays and Bordeaux mixtures are most effective.