Bartlett pears (Pyrus communis) are the most important pear of commerce, according to information published by the University of Georgia. These large, tasty pears are a cultivar of the European or common pear, which itself is is a hybrid of P. caucasia and P. nivalis. Bartlett pear trees are hardier than many other types of fruit trees. They tolerate poorer quality soil, for example, and even short periods of drought. Still, Bartlett pears are susceptible to a few fungal and bacterial diseases.
Bacterial Blight and Canker
Bacterial blight is caused by a bacteria (Pseudomonas syringae) that enters Bartlett pear trees either through a pruning wound, on an insect's body (such as boring insects) or a natural opening, such as a pollen tube. This bacteria thrives in cool, wet weather and often infects trees during rainy spring weather or through overhead irrigation. In European pear trees, bacterial blight affects the fruit of the tree only, causing cankers to appear (dead, sunken areas) on the skin of the fruit. These are not only unattractive, but render the fruit inedible unless the affected areas are cut out of the pears. It is not possible to cure this disease after it has infected the fruit of the tree, but it can be prevented by pruning only when the tree is dry, sterilizing pruning tools between cuts and sealing wounds. In addition, make sure the trees have plenty of air circulation around them so they do not stay wet for long periods of time.
Wood rots are caused by many different fungi, according to information published by the University of Illinois. This fungal disease, which attacks only dead wood, can kill a tree if the fungus infects the trunk of the tree rather than a branch. It can be difficult to tell if a tree is infected, as it may still produce foliage for years--even when rotted on the inside; the live sapwood will not be affected, but an obvious sign is the development of conks or toadstools on the trunk, especially at the base of the trunk. These structures house the developing fungal spores. Prevention of this disease is very difficult, as there are many fungi that cause wood rot. Well-draining soil will help prevent the fungi from overwintering or developing in the ground, and young trees can benefit from an application of fungicide in the spring. If you suspect your Bartlett pear tree is rotting on the inside, you may want to cut it down to prevent it from falling on its own, especially if the tree might be a danger to nearby people or structures.
Fire blight is caused by the pathogen Erwinia amylovora. The name comes from the appearance of the infected tree, which looks as if it has been singed on the outer edges by fire. In most plants, the disease causes new growth to become withered and brown. In Bartlett pear trees, the disease causes the fruit to shrivel up and turn black, deformed or simply fall off the tree. Fire blight moves inward and downward on a tree and is particularly prevalent during warm, wet springs. Prevent fire blight from developing by avoiding heavy pruning (Bartlett trees do not require heavy pruning anyway), sealing accidental wounds such as those caused by gardening tools and avoiding using a high-nitrogen fertilizer on young trees. Copper sprays can also be used to protect trees from the disease.