Fire blight is a bacterial disease that attacks raspberries, apple, crabapple, mountain ash,
cotone aster, saskatoon berry, and spirea. The blossoms of these trees and shrubs
suddenly turn brown and wilt. Later, the twigs may appear as if scorched by fire, and may
turn brown or black, curling into a characteristic "shepherd's crook". The leaves on
infected branches often remain on the trees all summer and well into the winter. The
disease also produces cankers, which are discolored areas that are slightly sunken and
tend to crack around the edges. These cankers may produce a slimy, bacterial ooze that
contains millions of bacterial cells. Flies, bees, ants, and beetles can spread these disease
cells from blossom to blossom and from tree to tree. The disease can also be spread by
rain, wind and pruning shears. Fire blight can develop during early summer when there
are alternating periods of rain and sunshine. Severe infections can ultimately be fatal to
some trees or shrubs.
Once fire blight has infected a tree or shrub, eradication is the only way to control it.
During the dormant period, prune out the infected plant material, cutting at least nine
inches below the diseased wood. Disinfect pruners between each cut by dipping them in a
solution of one part household bleach to nine parts water for ten seconds. Burn the
Prevent problems by planting resistant varieties, or spray existing plants with an
antibiotic such as Agristrep, every five to ten days during bloom. Excessive fertilization,
especially with nitrogen, can make plants susceptible to fire blight. Fertilize only when
soil tests show a nutrient deficiency. Rapid growth can make the tree or shrub susceptible
to other problems as well; steady growth is best.
Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon
State University. Corvallis, OR 97331-0817.
Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide.
1994. University of California. Oakland, CA 94608-1239. Pub. #3359. 327 pp.
Plant Health Guide. 1995. Meister Pub. Co. Willoughby, OH 44094-5992. 178 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press,
Ithaca, N.Y. 576 pp.
Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
Categories: Fire Blight, Disease, Tree