Fire blight is a bacterial disease that afflicts pear and apple trees in many parts of the U.S. The disease causes damage to blossoms and buds, preventing fruiting. As it spreads, it causes brown or blackened leaves and twigs. The twigs often curl downward resembling a shepherd's hook. Large cankers may form on the trunk and branches, or even on the roots of the tree. Left untreated, the disease may spread to main limbs and the trunk, eventually killing the tree.
Plant Disease-Resistant Trees
The simplest solution for fire blight is to plant disease-resistant trees. Resistant apple varieties include Spartan, Honeycrisp, Red Delicious, Haralson and NW Greening. Avoid Lodi, Braeburn, Jonathan, Jonagold and Gala, which are all susceptible to the disease. Resistant pear varieties include Keifer, Garber, Seckel, Tyson, Lincoln and Duchess. Some ornamental pear trees are susceptible to fire blight, while most crab apples are resistant.
Prune out dead and diseased limbs in late winter when the tree is dormant to minimize the chances of spreading the disease. Dip pruning tools in a solution of 1 part chlorine bleach to 10 parts water between cuts to disinfect tools. Monitor the trees carefully in late spring after petal fall, cutting out any branch tips that show signs of infection, especially those high in the trees. Removing twigs at the first sign of infection will slow or stop the spread of the disease. Discard or burn all diseased plant parts. Do not compost them or leave them on the property.
Weather patterns play a role in the spread and severity of fire blight. Outbreaks are more severe during wet spring weather, especially when daytime temperatures remain between 65 and 70 degrees Fahrenheit. Spray trees with Streptomycin, a bactericide, during bloom if conditions are favorable for the growth of fire blight. Make two applications, according to package directions.
Fire blight is more likely to occur on vigorously growing apple and pear trees. Apply nitrogen fertilizer judiciously, because excess nitrogen can cause vigorous growth. Apple trees should produce no more than 8 to 12 inches of new terminal growth per year; pears should produce no more than 6 to 8 inches of new growth. Cut back on nitrogen fertilizer if your trees produce rapid, leafy growth.
- West Virginia University Kearneysville Tree Fruit Research and Education Center; Fire Blight...; P.W. Steiner et al.
- University of Minnesota Extension; Disease-Resistant Apple Varieties; Jill D. Pokorny et al.; 2000
- University of Missouri Extension; Fire Blight; Christopher J. Starbuck and Michele R. Warmund; 2007
- Photo Credit Hemera Technologies/Photos.com/Getty Images
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