Extension Circular 68-1814 deals with fire blight.  Fire blight is a common and frequently destructive bacterial disease of certain plants belonging to the rose family

Weihing, J.

Whitney, W.

Wysong, D.

English

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnHistorical Materials from University of Nebraska-Lincoln Extension Extension1968EC68-1814 Fire Blight of Apples and PearsJ. WeihingD. WysongW. WhitneyFollow this and additional works at: http://digitalcommons.unl.edu/extensionhistThis Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted forinclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University ofNebraska - Lincoln.Weihing, J.; Wysong, D.; and Whitney, W., "EC68-1814 Fire Blight of Apples and Pears" (1968). Historical Materials from University ofNebraska-Lincoln Extension. 3904.http://digitalcommons.unl.edu/extensionhist/3904OF AGRICUL ' , LIBRARY FIRE BLIGHT OF APPLES AND PEARS J. L. Weihing, D. S. Wysong Extension Plant Pathologists W. C. Whitney Extension Horticulturist Fire blight is. a common and frequently destructive bacterial disease of certain plants belonging to the rose family. It is one of the most serious diseases of apple and pear. The bacterium that causes fire blight attacks as many as 75 other hosts, including quince, chokecherry, cotoneaster, crabapple, hawthorn, Japanese quince, loquat, mountain-ash, pyracantha, raspberry, rose, spirea, and strawberry. Varietal Susceptibility Apple and pear varieties differ in their reaction to fire blight. Local weather conditions also affect the amount of disease found in a variety from year to year. Table 1 shows varieties classified according to their degree of susceptibility. Table 1. Varieties and eCiree of susceptibili v to fire bliCiht. Moderately Host Susceptible susceptible Resistant Apple Jonathan Duchess Delicious Minjon Early Mel ntosh Winesap Secor Grimes Northwestern Greening Yellow Transparent Golden Delicious Beacon Haralson Cortland King David Prairie Spy Missouri Pippin Wealthy Turley Rome Beauty Sharon Pear Bartlett Douglas Magness Clapp's Favorite Garber Moonglow Flemish Beauty Kieffer Patten Seckel Cause and Symptoms Fire blight is caused by a bacterial organism, Erwinia amylovora, that lives from one season to the next in cankers on infected twigs, branches, or trunk. In the spring the bacteria multiply rapidly and start oozing to the surface of the "holdover" cankers in the form of clear, milky, or amber-colored droplets. Rains, wind, and insects (honey bees and bumblebees) all help to spread bacteria from the oozing cankers to the blossoms and new leaves. Infection of blossoms is favored by temperatures of 760F accompanied by precipitation or very high relative humidity. Infected blossoms wilt, turn brown and die. 2 Most of the leaf and twi.g blight infection is caused by bacteria which are blown through the air in bacterial strands. These strands become lodged in various portions of the tree. Rain dissolves the gelatinous strands, freeing the bacteria for entry into natural openings in the leaves and bark. Infected leaves usually are killed entirely, but occasionally only a portion will show infection. Leaves killed by fire blight will turn brown (apple) or black (pear) and remain attached to the tree (Figure 1). Figure 1. Terminal branch killed by fire blight bacteria. Newly infected twigs become watery, dark green and somewhat oily. The succulent tissue then dries, shrivels, darkens and the end of the twig bends over at the tip. The infected blossoms, leaves and twigs give the appearance of having been scorched by fire. Infection of branches and trunk results in the development of cankers. On the branches many of the cankers are found on the underside. At first the cankers are light brown in color and as they age the bark cracks and the canker surface becomes depressed (Figure 2). They may continue to enlarge until they girdle the branch or trunk, in which case the part above the girdle dies. Figure 2. Holdover cankers on young apple tree during dormant season (left) and following spring (right). 3 Control Losses from this disease can be reduced if growers and homeowners follow a blight-prevention program of sanitation and spraying. Sanitation: Remove and burn all twigs and branches having cankers since the fire blight bacteria overwinter in them. Cut out the diseased wood only while the trees are dormant in order to reduce the chances of spreading the bacteria on saws and cutting knives. When removing a diseased branch, the cut should be made at the junction of a lower, lateral branch at least a foot below the visible signs of the disease. Cankers on main limbs or on the trunk are removed by surgical meth-ods. The infected tissue is excised with a wood .chisel and mallet, tracing the canker abou.t.2 inches beyond the visible margins· (Figure 3). Remove all the diseased bark and scrape th~ wound clean to sound wood. The finished cut should be elongated with the grain and pointed at both ends to aid the healing process. All pruning tools should be disin-fected after each cut by dipping them into a 5-percent chlorox solution. This concentration is prepared by diluting 1 part of the commercial chlorox solution with 20 parts ot water. All fresh cuts and wounds should be painted with a good asphalt-base tree wound dressing or !2~) Figure 3. Large trunk or branch cankers can be removed by surgically excising the diseased tissue with a wooden mallet and chisel. Spraying: Commercial antibiotics are available to orchardists and homeowners alike. Streptomycin when applied at a dosage of 50-100 parts per million, is an effective spray material for controlling fire blight. It should be applied first at the pink stage (3-4 days before blossoms open) and repeated every 5-7 days for about 3 weeks. A commercial formulatio[l including streptomycin is available under the trade name Agrimycin 17 (streptomycin sulphate plus oxytetracycline). Zineb (1 1/3 tablespoons per gallon of water) or Bordeaux mixture (1-3-100) will help to protect open blossoms against the fire blight bacterium also. A spray schedule should be followed similar to that using streptomycin. Fertilization: Rapidly growing twigs which have been stimulated by excessive fertility or heavy pruning are extremely susceptible to infection. Therefore, it is best to use either manure or one of the slow-release fertiliz.ers on young trees and susceptible varieties. 4 

EC68-1814  Fire Blight of Apples and Pears

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University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Historical Materials from University of Nebraska-
Lincoln Extension Extension
1968
EC68-1814 Fire Blight of Apples and Pears
J. Weihing
D. Wysong
W. Whitney
Follow this and additional works at: http://digitalcommons.unl.edu/extensionhist
This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for
inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University of
Nebraska - Lincoln.
Weihing, J.; Wysong, D.; and Whitney, W., "EC68-1814 Fire Blight of Apples and Pears" (1968). Historical Materials from University of
Nebraska-Lincoln Extension. 3904.
http://digitalcommons.unl.edu/extensionhist/3904
OF AGRICUL ' , 
LIBRARY 
FIRE BLIGHT OF APPLES AND PEARS 
J. L. Weihing, D. S. Wysong 
Extension Plant Pathologists 
W. C. Whitney 
Extension Horticulturist 
Fire blight is. a common and frequently destructive bacterial disease of 
certain plants belonging to the rose family. It is one of the most serious diseases 
of apple and pear. 
The bacterium that causes fire blight attacks as many as 75 other hosts, 
including quince, chokecherry, cotoneaster, crabapple, hawthorn, Japanese 
quince, loquat, mountain-ash, pyracantha, raspberry, rose, spirea, and 
strawberry. 
Varietal Susceptibility 
Apple and pear varieties differ in their reaction to fire blight. Local weather 
conditions also affect the amount of disease found in a variety from year to 
year. Table 1 shows varieties classified according to their degree of susceptibility. 
Table 1. Varieties and eCiree of susceptibili v to fire bliCiht. 
Moderately 
Host Susceptible susceptible Resistant 
Apple Jonathan Duchess Delicious 
Minjon Early Mel ntosh Winesap 
Secor Grimes Northwestern Greening 
Yellow Transparent Golden Delicious 
Beacon Haralson 
Cortland King David 
Prairie Spy Missouri Pippin 
Wealthy Turley 
Rome Beauty Sharon 
Pear Bartlett Douglas Magness 
Clapp's Favorite Garber Moonglow 
Flemish Beauty Kieffer 
Patten Seckel 
Cause and Symptoms 
Fire blight is caused by a bacterial organism, Erwinia amylovora, that lives 
from one season to the next in cankers on infected twigs, branches, or trunk. 
In the spring the bacteria multiply rapidly and start oozing to the surface of 
the "holdover" cankers in the form of clear, milky, or amber-colored droplets. 
Rains, wind, and insects (honey bees and bumblebees) all help to spread bacteria 
from the oozing cankers to the blossoms and new leaves. 
Infection of blossoms is favored by temperatures of 760F accompanied by 
precipitation or very high relative humidity. Infected blossoms wilt, turn brown 
and die. 
2 
Most of the leaf and twi.g blight infection is caused by bacteria which are 
blown through the air in bacterial strands. These strands become lodged in 
various portions of the tree. Rain dissolves the gelatinous strands, freeing the 
bacteria for entry into natural openings in the leaves and bark. Infected leaves 
usually are killed entirely, but occasionally only a portion will show infection. 
Leaves killed by fire blight will turn brown (apple) or black (pear) and remain 
attached to the tree (Figure 1). 
Figure 1. Terminal branch killed by fire blight bacteria. 
Newly infected twigs become watery, dark green and somewhat oily. The 
succulent tissue then dries, shrivels, darkens and the end of the twig bends over 
at the tip. The infected blossoms, leaves and twigs give the appearance of having 
been scorched by fire. 
Infection of branches and trunk results in the development of cankers. On 
the branches many of the cankers are found on the underside. At first the 
cankers are light brown in color and as they age the bark cracks and the canker 
surface becomes depressed (Figure 2). They may continue to enlarge until they 
girdle the branch or trunk, in which case the part above the girdle dies. 
Figure 2. Holdover cankers on young apple tree during dormant season (left) and following 
spring (right). 
3 
Control 
Losses from this disease can be 
reduced if growers and homeowners 
follow a blight-prevention program of 
sanitation and spraying. 
Sanitation: Remove and burn all 
twigs and branches having cankers 
since the fire blight bacteria 
overwinter in them. Cut out the 
diseased wood only while the trees are 
dormant in order to reduce the 
chances of spreading the bacteria on 
saws and cutting knives. When 
removing a diseased branch, the cut 
should be made at the junction of a 
lower, lateral branch at least a foot 
below the visible signs of the disease. 
Cankers on main limbs or on the 
trunk are removed by surgical meth-
ods. The infected tissue is excised 
with a wood .chisel and mallet, tracing 
the canker abou.t.2 inches beyond the 
visible margins· (Figure 3). Remove all 
the diseased bark and scrape th~ 
wound clean to sound wood. The 
finished cut should be elongated with 
the grain and pointed at both ends to 
aid the healing process. 
All pruning tools should be disin-
fected after each cut by dipping them 
into a 5-percent chlorox solution. 
This concentration is prepared by 
diluting 1 part of the commercial 
chlorox solution with 20 parts ot 
water. All fresh cuts and wounds 
should be painted with a good 
asphalt-base tree wound dressing or 
!2~) 
Figure 3. Large trunk or branch cankers 
can be removed by surgically excising the 
diseased tissue with a wooden mallet and 
chisel. 
Spraying: Commercial antibiotics are available to orchardists and 
homeowners alike. Streptomycin when applied at a dosage of 50-100 parts per 
million, is an effective spray material for controlling fire blight. It should be 
applied first at the pink stage (3-4 days before blossoms open) and repeated 
every 5-7 days for about 3 weeks. A commercial formulatio[l including 
streptomycin is available under the trade name Agrimycin 17 (streptomycin 
sulphate plus oxytetracycline). 
Zineb (1 1/3 tablespoons per gallon of water) or Bordeaux mixture (1-3-100) 
will help to protect open blossoms against the fire blight bacterium also. A spray 
schedule should be followed similar to that using streptomycin. 
Fertilization: Rapidly growing twigs which have been stimulated by 
excessive fertility or heavy pruning are extremely susceptible to infection. 
Therefore, it is best to use either manure or one of the slow-release fertiliz.ers on 
young trees and susceptible varieties. 
4 


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