Both bacterial and fungal diseases can affect ornamental pear trees, causing deformed leaves and blossoms or the die-back of branches. Some diseases may even result in the death of the infected tree. A combination of good cultural practices and chemical treatments will work to prevent and control many diseases.
The bacterial disease fire blight can cause significant problems for ornamental pears. Fire blight appears in the spring during wet, humid conditions after the tree has begun flowering. Insects spread the disease by consuming bacteria on cankers of infected plants. The bacteria become less active during cool, dry weather. Flowers and leaves turn brown and wilt, but remain on the tree. Branches turn black as the disease progresses. Prune 8 to 10 inches below infected areas of the tree during the dormant season. Use clean, sharp pruning tools and disinfect the tools between each cut to prevent spreading the disease. Sterilize tools using rubbing alcohol or a solution of 1 part bleach to 9 parts water. New growth is most susceptible to this disease, so avoid fertilizing ornamental pears during the spring. Fertilize lightly only in the fall. Apply copper fungicides in the winter and products containing streptomycin during the growing season.
Entomosporium Leaf Spot
The fungal disease entomosporium leaf spot causes small red spots to appear on older leaves of ornamental pear trees. As these spots grow, clusters of white spores appear in the center of the spots. Pear trees will prematurely drop their leaves if infected with this disease. Prune back diseased foliage and remove it from the garden. Disinfect pruning tools and pick up and dispose of any fallen foliage to avoid spreading the disease to other plants. Properly space ornamental pears and avoid planting groundcover beneath the trees to increase air circulation. Overhead watering may further spread the disease. If necessary, apply fungicides containing copper or chlorothalonil.
Bacterial Blight and Canker
Bacterial blight causes the formation of black lesions on the stems and flowers of ornamental pears. Cankers also form on the branches, and this may cause the death of the tree. This disease occurs during particularly wet spring conditions. Chemical treatments do not provide relief from bacterial blight. Prune back and discard diseased branches. Water the soil at the base of the tree and avoid getting the leaves wet. If cankers appear, the tree will likely die and removal may be necessary.
Cotton Root Rot
The soil-borne fungus cotton root rot, also known as Texas root rot, causes the entire taproot of an ornamental pear tree to rot. Leaves wilt and the tree may die suddenly. No chemical treatments can control cotton root rot. If you suspect this disease has infected your ornamental pear tree, take a section of the root system to an extension office for diagnosis. Remove infected trees and plant only disease-resistant plants in the area where the fungus is present.