I have a pear tree that has several branches that suddenly turned brown and died back. What would cause this?
It sounds as though your pear tree has fire blight, a bacterial disease that can infect trees during bloom or during the growing season. It's more severe during warm, wet weather. Symptoms include brown or black leaves that cling on the tree. The tips of branches often curl into a shepherd's crook. In severe cases, the entire tree may be killed.
In addition to pears, other members of the rose family-apple—such as crabapple, pyracantha, and cotoneaster—are susceptible. Control can be difficult. Avoid pruning susceptible trees and shrubs during the growing season. Open wounds provide an entry point for the bacteria. However, if the disease gets started, pruning out affected branches can stop its spread. Prune 8-12 inches below the blackened area. Sterilize your pruning tool between each cut by dipping the cutting mechanism in a solution of 1 part chlorine bleach to 9 parts water.
To prevent metal parts from corroding, rinse tools thoroughly with water before putting them away. Avoid fertilizing your pear tree. It may be getting excess nutrients from lawn fertilizer applied nearby. Succulent growth from high-nitrogen fertilizer is more susceptible to fire blight attack.