The leaves of a pear tree are often among the first parts of the tree to show distress when disease is present. Damage to the pear tree's leaves can be indicative of a number of disorders, ranging from fungal infections to the presence of destructive insects. By diagnosing the problem and treating it promptly, you may be able to restore your pear tree to health and still produce a crop of fruit for the year.
Examine the pear tree's leaves. Note any signs of distress, such as spots or ragged edges. Dark fecal pellets on the underside of the leaves, for instance, may indicate the presence of thrips, an insect that is only 1/25 inch long, but which may cause considerable damage to the tree's leaves. Yellow leaves may be indicative of psyllids, insects that produce a honeydew that attracts fungal molds. Write down the symptoms you observe.
Look for the presence of insects. Some insects, such as the thrips mentioned in Step 1, may be too small to see. Others, however, are fairly visible, such as the tarnished plant bug, a 1/4-inch-long brown insect that is mottled with yellow and black. Its eggs are long and can be found on the tree's stems and leaves. This insect will feed on the tree and may cause blackening of the shoots and ruin the pear tree's flowers. Write a description of any insects you find on the tree's leaves. Search for them on the undersides of the leaves or tucked into furls.
Contact a local plant disease clinic or the county extension center of a local agricultural university. Prepare a leaf sample to deliver to them. Place the leaves in a small paper bag, then place the paper bag into a plastic recloseable freezer-storage bag. Keep the sample in a refrigerator until it's ready to ship or deliver. Provide the written description of any symptoms or insects you've observed, along with the leaf sample. The center will diagnose the problem and offer suggestions for treating it.