When apple or pear branch tips look scorched, with brown or black leaves hanging on them, a likely explanation is the disease “fire blight”, caused by the bacterium Erwinia amylovora. This aptly named disease seriously damages plants in the Rose family, especially apples and pears, seldom stone fruits, and many ornamentals (Figure 1). In commercial orchards, economic losses can be severe. In backyards, limbs die back and fruit is lost. Small trees may die.


Flowers and succulent shoots are usually affected first. Symptoms are a water- soaked appearance then a sudden wilting of succulent tips, followed by the shriveling of infested leaves, shoots, blossoms, and eventually fruit. Infected twigs typically form a “shepherd’s crook”.

The infection spreads from the flower to the fruiting spur, then to leaves, and ultimately to the woody tissue around the spur. Tips of limbs are infected and show symptoms first. The leaf stem (petiole) and midrib characteristically blacken and yellow bacterial ooze may occur on the leaf. Diseased apple leaves generally turn brown, while infected pear leaves turn black.
Cankers, can form on twigs and branches, eventually spreading into the trunk. Cankers are at first slightly sunken small brown to black areas. These may crack during the dormant season.

During the growing season the active edges of the cankers may appear raised or blistered and become more defined. The internal wood under and around the cankers becomes discolored with reddish brown streaks. These cankers may girdle the branch, killing it.

A tan-yellow bacterial slime is forced out of infected areas. The bacteria are then easily dispersed by insects and splashing water. This sugary bacterial ooze clogs the water carrying vessels of plants causing wilting.

Immature fruit can become infected with bacteria through natural openings in the skin, wounds, or infected fruiting spurs. Infected fruit first appears gray green, and water-soaked, then turns black. Sometimes a whitish to light tan fluid seeps out of the fruit. Eventually, fruit dries and shrivels on the tree.

Compared to its rate in flowers and fruit, the disease progresses more slowly in woody tissue, but once in the trunk, Erwinia amylovora can kill a tree.


Bacteria over-winter in the tissue under the bark at the margins of cankers. As the weather warms in spring, bacteria become active and form a sticky bacterial flow.


Bacteria may be spread in many ways. Birds, flies, pollinators and other insects crawl through or ingest this material and infect flowers, wounds, and natural leaf and twig openings. Insect vectors of the disease include ants, aphids, bees, houseflies, pear psylla, leafhoppers, and shothole borers among others. The host range includes over 200 species in nearly 40 genera.
Splashing water, either from rain or overhead irrigation, is another common way the disease is spread. Wind also carries bacteria.

Humans are often at fault for disseminating the inoculum by unsanitized pruning tools.

Blight symptoms appear within one to three weeks of infection, depending on temperature and moisture.


Warm weather, 65 °F or higher in a 24-hour period and humidity of 65% or higher during bloom greatly favor disease development, although fire blight can grow over a much wider range of 39-90 °F. Epidemics often occur following rain or hail storms where twigs and branches have suffered injury. Precipitation promotes development and dissemination of the disease. Sprinkler irrigation, high nitrogen fertilizers, severe pruning, and other factors that favor succulent new growth can all stimulate the disease.


Cultural practices:

Buy only fire blight resistant varieties and avoid susceptible plants. This is the first priority in preventing or controlling fire blight. Plant trees and shrubs in soil with good drainage to avoid stress that makes plants more susceptible to the disease.

For the complete article use the link below.


Skelly, J., and O'Callaghan, A. 2001, Fire Blight, Extension, University of Nevada Reno, FS-01-56

Learn more about the author(s)


Also of Interest:

Non-Chemical Rodent Control
Rodents are one of the main pests in urban areas, and can cause various problems in homes and businesses.This publication focuses on ways to manage rodent populations in the urban setting without using common chemical products. It explores aspects of exclusion, trapping and other...
Kerns, W. A., Robinson, M. L., and Ryan, M. 2002, Extension, University of Nevada Reno, SP-02-10
Tomatoes showing blossom end rot.
Recognizing Plant Nutrient Deficiencies
There are 14 essential nutrients for plants, and when plants lacks one, it displays certain symptoms. This fact sheet explains how essential nutrients act in plants, and the symptoms of deficiencies.
O'Callaghan, A. 2002, Extension, University of Nevada Reno, FS-02-65
roses on arbor
Different rose varieties need different pruning
How to prune different varieties of roses.
Fisher, J. 2018, Reno Gazette Journal
Managing Sooty Canker
Sooty canker is one of the few bacterial diseases that affects woody plants in the desert. This disease has many possible hosts, from many different plant families. It is not easy to control, and this fact sheet provides guidance for households trying to deal with it.
Johnson, W. S., Morris, R. and Mandekic, J. 1996, Extension, University of Nevada Reno, FS-96-26
Chard at DFI
Division of Plant Health and Compliance-Plant Pathology Fact Sheets
These fact sheets offer a variety of plant health and pathology information.
Nevada Department of Agriculture (NDA) 2006, NDA (

Associated Programs

master gardeners in garden

Master Gardeners of Washoe County

Master Gardeners provide free, research-based horticulture information to Nevadans.

Master Gardeners at tabling event

Master Gardeners of Nevada

Program trains local gardeners to provide research-based horticulture information to Nevadans

pesticide traing cb

Pesticide Safety Education Program

Extension’s Pesticide Safety Education Program provides web-based training for pesticide applicators seeking to apply restricted and general use pesticides safely, properly and according to the law. Pesticide licensure and certification is administered by the Nevada Department of Agriculture.