BP-30-W
Ornamental Diseases

Cooperative Extension Service
Purdue University
West Lafayette, IN

Fire Blight

Paul C. Pecknold, Extension Plant Pathologist
Fire blight is a bacterial disease that is particularly destructive on many varieties of apple and pear. It may also damage certain ornamental plants, such as flowering crabapple, hawthorn, mountain ash, cotoneaster, pyracantha, and spirea. If not controlled, fire blight can destroy the blossoms and fruit and may damage or kill the plant by stem infection.

Symptoms

Fire blight usually first appears during bloom. The blossom clusters wilt and turn dark brown or black. This is followed by twig blight infection of the current season's growth. The most obvious symptom of twig blight is a scorched appearance of affected stems in which the leaves wilt, turn brown, and cling to the stem. It is this stage that gives the disease the name "Fire Blight."

Often the tips of blighted twigs have a crooked appearance resembling a fish hook. Fire blight may continue to spread downward from the blighted twigs into main scaffolding limbs and trunk. The outer bark of infected branches becomes shriveled, while the inner bark appears water-soaked and reddish-brown. There is usually a distinct separation of the infected (cankered) and healthy tissue. The cankered areas are often slightly sunken and have a darker appearance than that of adjacent healthy bark tissue.

Cause

Fire blight is caused by the bacterium, Erwinia amylovora. The bacteria overwinter in cankered limbs, and in spring, droplets of sticky, amber-colored ooze form from these cankers. These droplets contain large numbers of bacteria. Insects and spattering rain carry the bacteria from the droplets to blossoms and twigs. More fire blight bacteria ooze from these new infections, and insects and rain again carry them to new areas of the tree and orchard. Fire blight is most damaging in years when spring temperatures are above normal with frequent rains. During cool springs the blossoms blight phase is usually not significant.


Figure 1: Blighted twig showing typical crooking of the apical

Control

No single practice can insure complete control of fire blight. However, you can reduce the disease if you employ a combination of both cultural and chemical control measures as outlined below.

Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may be similar. Persons using such products assume responsibility for their use in accordance with current label directions of the manufacturer.


REVISED 5/01

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