Pyrathanca: Fireblight

Problem
Blossoms and leaves of infected twigs suddenly wilt and turn black as if scorched by fire. The leaves curl and hang downward. The bark at the base of the blighted twigs becomes water soaked, then dark, sunken, and dry; cracks may develop at the edge of the sunken area. In warm, moist spring weather, drops of brown ooze appear on the sunken bark. Young plants may die.

Analysis
This disease is caused by a bacterium (Erwinia amylovora) that is very destructive to many trees and shrubs. (For a list of susceptible plants, see Plants Susceptible to Fire Blight.) The bacteria spend the winter in the sunken areas (cankers) on the branches. In the spring, the bacteria ooze out of the canker. Bees, flies, and other insects are attracted to the sweet, sticky ooze and become smeared with it. When the insects visit a flower for nectar, they infect it with the bacteria. The bacteria spread rapidly through the plant tissue in warm (65°F or higher), humid weather. Insects visiting these infected blossoms later carry bacteria-laden nectar to healthy blossoms. Tender or damaged leaves may be infected in midsummer.

Solution
During spring and mid- to late summer, prune out infected branches 12 to 15 inches beyond any visible discoloration and destroy. A protective spray of a bactericide containing basic copper sulfate or streptomycin, applied before bud break in spring, will help prevent infection. Repeat at intervals of 5 to 7 days until the end of bloom. In the fall, prune out infected branches. Sterilize pruning shears after each cut with rubbing alcohol. For a list of pyracantha varieties resistant to fireblight, see Pyracanthas and Hawthorns Tolerant of Fire Blight.