The Bradford pear is native to Korea and China; it was introduced to Western horticulture in 1908. It is thornless and known for its beautiful pyramidal shape and lovely white spring flowers. The flowers although beautiful in appearance have an unpleasant smell. Problems with the Bradford pear are: splitting at branch junctures and a short life span (15 to 25 years). Diseases are fire blight and Entomosporium leaf spot.
This is a bacterial disease that affects some fruit trees (pear and apple) as well as some ornamental trees such as: flowering crabapple, hawthorn and mountain ash. If fire blight is not treated it will kill the flowers and fruit, and possibly destroy the tree. Symptoms of the blight appear in early spring when the tree is beginning to blossom. The flowers of the Bradford pear wilt and their color changes to dark brown or black. Infected stems will appear scorched, and this is how “fire blight” got its name. Leaves wilt and their color changes from green to brown. The leaves cling to the twigs.
The ends of the infected stems/twigs curl up, taking on the shape of a fish hook (crooked). The disease can spread into the limbs and trunk of the Bradford pear. Outer bark tissue of the infected branches and trunk areas show signs of the disease by their shriveled appearance. Inner bark tissue is reddish-brown in color and water-soaked.
How It Spreads
The bacteria survive through the winter, and remain present in cankered limbs. In springtime the cankers ooze an amber liquid containing the bacteria. The bacteria spreads by insects and rain. Fire blight is more severe in years where there are high amounts of rain and high temperatures.
Pruning infected branches and limbs in late winter can control fire blight. If you need to prune during the growing season care must be taken--pruning tools must be disinfected with bleach or alcohol to avoid further spreading of the disease. Chemicals can also be used to control fire blight. Agri-Strep (streptomycin) should be applied when the tree is flowering. Several applications of the Agri-Strep may have to be applied, depending upon how long it takes the tree to blossom.
Entomosporium Leaf Spot
Leaf spot is caused by a fungi known as Entomosporium maculatum. This disease is most active during the period when the tree is producing new growth and when the weather is cool and wet. Symptoms of leaf spot are red spotting on the top and bottom surfaces of young leaves, and brown or light gray spotting on mature leaves. Generally this is just cosmetic and does not severely harm the tree. In cases of extreme leaf spot the tree can loose a large amount of its foliage and there is a possibility that the tree may die.
Controlling Leaf Spot
Fungicides can be applied to control the disease, and care should be taken to remove diseased leaves. This disease is spread by spores that are present in the spots that appear on the leaves. Be careful not to wet the leaves as water will spread the spores. Since wet conditions promote the disease, be sure to water midday so that the leaves have time to dry. Keep fertilization to a minimum--discouraging new growth.