Cooperative Extension Service
West Lafayette, IN
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.
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.
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
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.
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