Pear trees are common throughout the United States, especially in colder northern states since they are quite cold hardy. Pears work well for baking, savory dishes and snacking. Leaf diseases on pear trees range from those that primarily impact the tree's cosmetic appearance to serious diseases that can ruin the pear crop or kill the tree.
Pear scab, sometimes called black spot, affects pear trees throughout North America, though the disease is worse in Japan and Europe. Initial symptoms occur on leaves; they develop round brown lesions that take on a velvety feel over time. Spores grow in the lesions, then small dots appear on the underside of leaves. Affected fruit develops dark brown blisters. To control this fungal disease, gardeners can spray trees with fungicides that target apple scab or pear scab. They can also plant disease-resistant varieties of pear.
Powdery mildew causes the leaves of pear trees and many other fruit trees to develop a thin white residue. The fine white mildew spots cover the top of the leaf. The leaves also dry out and curl or crinkle. This disease occurs primarily in wet spring weather. Pear trees bear less fruit--and the quality is worse--and display reduced growth when afflicted. Gardeners can treat this disease with approved fungicides and should check with their county extension office before spraying to obtain a list of currently approved fungicides that treat powdery mildew.
Pear decline can kill affected pear trees quickly, often over a matter of weeks, or slowly, taking several seasons. Gardeners cannot take action against quick decline but can manage trees with slow decline to obtain a few more years of pear crops. Trees affected with quick decline develop bright red leaves that wilt and die. Those with slow decline develop smaller leaves, grow fewer of them and generally display less vigor. Gardeners should plant pear trees with Pyrus communis rootstock or other tolerant rootstock. They should nurture trees affected with slow decline by providing them sufficient water, fertilization and care to keep them alive as long as possible.
Fire blight is a bacterial disease affecting apples, quince and pears. Affected shoots and limbs ooze a sap that turns dark brown or black and stains the wood. Blossoms and leaves shrivel and die, turning black. They remain on the tree throughout the season, giving it a scorched appearance. This disease occurs most often in wet, humid weather. Gardeners can plant less susceptible pear cultivars (like Bradford or Capitol). To control this disease, prune out affected wood and spray trees with copper fungicides to prevent new infection.
All pear trees benefit from a routine of best care practices that keep the tree healthy and less susceptible to disease. Plant pear trees where they will receive full sun and well draining soil. Fertilize the trees regularly with a balanced fertilizer and provide at least 1 inch of irrigation weekly. Prune the trees annually in late winter or early spring to remove dead or damaged wood and thin out the tree canopy, promoting air circulation and light. This helps push disease through the tree canopy so pear trees are less susceptible to leaf diseases.