Question: My pear trees are suffering from severe fire blight. How should I treat this disease and can I save my trees?
Answer: Fire blight (Erwinia amylovora) is a devastating bacterial disease that affects many plants, but especially apples and pears. As described by MSU Extension publication 736, fire blight leaves apple and pear trees with leaves and twigs that look as if they have been burned. Fire blight bacterium attacks leaves, twigs, and fruit and is spread by wind-blown rain and insects. Because the bacteria overwinter in cankers on limbs and blighted twigs left on the tree, the best control is removing all affected twigs and limbs during the dormant season.
If the infection is severe, go ahead and prune now; because if the blighted areas are not removed, then the fast-spreading infection can seriously harm the tree and the root stock. The dilemma about pruning during the growing season is that it will likely spread the disease even more! So, to avoid spreading the disease, you must dip your pruning equipment into a 10 % household bleach for a minute after each cut to prevent spreading the bacteria from one cut to another. It is best to use a pair of pruners, leaving one pruner in the bleach solution while making a cut with the other pruner and then switching back and forth. Sterilization of equipment is not necessary if pruning during the dormant season.
To prune, cut through healthy wood well below the blighted area. Cut out any blighted areas on large limbs down to healthy tissue. To be sure none of the blighted areas have been missed, reinspect the tree in the fall after the leaves have fallen and remove any holdover areas. Remove and burn all diseased prunings. During wet and humid weather (conditions that aid bacteria), pruning should not be attempted.
Avoid excessive nitrogen fertilization around infected trees, which will lead to vigorous shoot growth. Shoots that grow quickly are more susceptible to fire blight compared to those that grow slowly. A copper spray during the dormant season can help protect pear trees. Antibiotics are available as well; but use with caution, as resistance can occur. Choose pear trees with resistance to fire blight such as Magness, LeConte and Moonglow (purple pear). Orient (Asian pears) and Maxine have some resistance; Kieffer pears have little resistance. New varieties may be available, check the label or call your extension office if unsure about fire blight resistance.
Information for this article was obtained from James Shannon, Extension Agent; MSU Fruit and Nut Blog: “Fire Blight: Pros and Cons of Removal During the Growing Season”; MSU Publication IS1433: Fruit and Nut Review; MSU Publication 736: Homeowner Apple and Pear Insect and Disease Control.
Do you have a gardening question? Call the Pontotoc Extension Service at 662-489-3911 and ask to leave a question for the Master Gardeners. Pontotoc County Master Gardeners are trained volunteers who help the MSU Extension Service and serve the citizens of Pontotoc County.