no. 2.907

Fire Blight

by R.D. Koski and W.R. Jacobi 1 (10/09)

Quick Facts...

  • Fire blight is a bacterial disease that can kill branches and whole plants of many members of the rose family, including apple, pear, quince and crabapple. .
  • Symptoms include dead branches, water-soaked blossoms, light brown to blackened leaves, discolored bark, black “shepherd’s crook” twigs, and dried fruits. .
  • Fire blight bacteria can be spread by insects, splashing rain or contaminated pruning tools..
  • Management includes resistant varieties, cultural practices, pruning and preventive chemical sprays.

Fire blight is a bacterial disease that affects certain species in the rose family (Rosaceae). It is especially destructive to apples (Malus spp.), pears (Pyrus spp.), and crabapples (Malus spp.). The disease also can occur on serviceberries (Amelanchier spp.), flowering quinces (Chaenolmeles spp.), cotoneasters (Cotoneaster spp.), hawthorns (Crataegus spp.), quinces (Cydonia spp.), pyracanthas (Pyracantha spp.), blackberries (Rubus spp.), raspberries (Rubus spp.), and mountain ashes (Sorbus spp.).

Disease incidence varies from year to year and severity is influenced by cultivar susceptibility, tree age, succulence of tissues and spring meteorological conditions. The disease is most serious when spring temperatures during pre-bloom and bloom are warmer than average. Warm rainy springs are particularly conducive to rapid spread of the pathogen, resulting in blossom blight. Blight of twig terminals can occur in late May through June during wind driven rain events. Hail and wind damage provide wounds that allow the pathogen to enter at other times. Hot summer weather generally slows or stops the disease.

Disease Cycle

Fire blight is caused by the bacterium Erwinia amylovora. The bacteria overwinter in blighted branches and at the edge of cankers (areas of bark killed by bacteria) (Figure 1). In spring, when temperatures frequently reach 65 F, the bacteria multiply rapidly.

Fire blight life cycle
Figure 1: Fire blight life cycle.

Masses of bacteria are forced through cracks and bark pores to the bark surface, where they form a sweet, gummy exudate called bacterial ooze. Insects such as aphids, ants, bees, beetles, and flies, are attracted to this ooze, pick up the bacteria on their bodies, and inadvertently carry the bacteria to opening blossoms. Bacterial ooze splashed by rain can also spread the pathogen.

Once in the blossom, bacteria multiply rapidly in the nectar and eventually enter the flower tissue. From the flower, the bacteria move into the branch. When the bacteria invade and kill the cambial tissue of the branch, all flowers, leaves and fruit above the girdled area die.

Infection also can take place through natural openings in leaves (stomata), branches (lenticels), pruning wounds, insect feeding and ovipositing, and hail. Droplets of bacterial ooze can form on twigs within three days after infection.

Diagnosis

Blighted leaves on ornamental apple.
Figure 2: Blighted leaves on ornamental apple.

Symptoms of fire blight are first seen about the time of petal fall. Infected blossoms appear water-soaked and wilt rapidly before turning dark brown; this phase of the disease is referred to as blossom blight. As the bacterial invasion progresses, leaves wilt, darken and remain attached to the tree (Figure 2); this gives the tree a fire-scorched appearance, thus the name “fire blight.”

Infected twigs darken and branch tips may bend over forming a “shepherd’s crook.” During wet conditions infected tissue may exude creamy bacterial ooze in droplets or fine, hair-like strands. Infected fruits also exude bacterial ooze. Rather than dropping from the tree, infected fruits gradually dry and remain attached to the branch.

Sunken black canker on apple branch
Figure 3: Sunken black canker on apple branch.

Fire blight cankers on branches or stems appear as dark discolored areas that are slightly sunken, with a narrow callus ridge along the outer edge (Figure 3). The narrow callus ridge is diagnostic for differentiating fire blight cankers from fungal cankers. Under the bark associated with a canker, the inner bark turns from green to brown, but the appearance varies depending on plant variety. Droplets of bacterial ooze may appear on the canker.

Disease Management

There is no cure for this disease, so prevention is the best solution for the management of fire blight. Fire blight management methods include: planting resistant varieties, implementing cultural practices that favor growth of the plant rather than the pathogen, pruning to remove infected plant parts, and chemical sprays. Using resistant varieties is the most effective prevention method. Spraying chemicals is not recommended for homeowners because of chemical availability, potential phytoxicity and the critical timing of sprays.

Resistant varieties: Cultivars of apple, crabapple, and pear differ in their degree of susceptibility to the bacterium (Table 1) although some cultivars are less susceptible than others, no cultivar is immune to infection when the pathogen is abundant and conditions are favorable for infection. Avoid blight susceptible apple rootstocks especially when grafted to susceptible scions (Table 2). To minimize stress that may predispose the tree to other disease-causing agents, select varieties adapted to the growing area. Local weather conditions from year to year also affect the amount of fire blight found in a variety.

Cultural practices: Minimizing rapid growth and succulent tissue will reduce the risk of fire blight developing on the susceptible young, succulent tissue. Annual pruning with avoidance of major cuts will help minimize tree vigor. Similarly, limiting the amount of nitrogen fertilizer will reduce twig terminal growth. Fertilization should be based on the results of foliar and/or soil nutrient analysis and should not be applied in excess.

Pruning: Remove all blighted twigs and cankered branches. Prune twigs and branches 8 to 12 inches below the edge of visible infection. CAUTION! After each cut, surface sterilize all tools used in pruning. Dip tools in household bleach or ethyl alcohol, or use household spray disinfectants. Spreading the blight bacteria risk is lowered if pruning is delayed until mid winter. Winter pruning can also be accomplished more efficiently because pruning tools need not be disinfected between cuts if pruning is done when trees are fully dormant. To decrease the chance of new infections, promptly remove from the site and destroy all infected branches.

To remove a canker that does not extent more than 50 percent around a large stem, first make a cut through the bark down to the wood 1 to 2 inches outside the canker margin. The cut should not have any sharp angles. Next, cut and scrape away all infected bark down to the wood. Treat exposed wounds with a 70 percent alcohol solution. The whole stem should be removed if a canker extends around more than 50 percent of the stem.

During pruning, take care to avoid unnecessary wounds to the tree. When climbing trees, wear soft-soled shoes to prevent bark injuries.

Remove fire blight infected branches during summer only if the following conditions exist:

  • Infections are in young, vigorous trees and the bacteria may girdle the main stem or main branches.
  • Infections are in dwarfing trees on highly sensitive rootstocks, such as M.9 or M.26.
  • The number of infections in older trees is limited and can easily be removed.
  • It is a dry, sunny day when there is no chance of rain for 48 hours.

Chemical sprays: Chemical sprays are preventive treatments that must be applied prior to the onset of fire blight symptoms; sprays have little effect after the onset of symptoms. Expect blossom infections and plan to apply chemical sprays if: temperatures remain between 65 F and 86 F for a day or more during flower bloom, there is at least a trace of rainfall, the relative humidity remains above 60 percent for 24 hours, there is abundant succulent shoot growth, or there are fruit injuries from hail or other agents. For specific instruction on sprays and timing please use the Midwest Tree Fruit Spray Guide. The chemicals may be sold on various trade names.

Streptomycin is an antibiotic that is acceptable for use to protect trees but may be difficult to obtain. Do not use streptomycin after symptom development since it may lead to antibiotic resistance in the bacterial population.

Aluminum tris is a bactericide used prior to and during bloom.

Copper sprays are toxic to many species of bacteria. Copper sprays are best used during dormancy and prior to bud break because they may damage leaves and young fruit. Do not apply sprays within 50 days of apple harvest or within 30 days of pear harvest. Do not mix with oils or phytotoxicity issues can occur. Copper is available in several forms and sold under various trade names, including Bordeaux mixture.

Prohexadione-calcium is a plant growth regulator that reduces longitudinal shoot growth by inhibiting gibberellin biosynthesis. Prohexadione-calcium does not possess antibacterial activity but alters host biochemistry and tissues in ways that are not favorable for infection by E. amylovora. The length of time that shoot growth is inhibited depends on the application rate and tree vigor. Prohexadione-calcium is ineffective for control of the blossom blight phase of fire blight.

Biocontrol: Blight Ban is a formulation of the bacteria Pseudomonas fluorescens, strain A506, and is effective in controlling the growth of the fire blight bacterium when applied before and during bloom. It is available only in quantities for commercial application. Effectiveness of control by Blight Ban is dependent on proper application timing.

Table 1: Varietal susceptability to fire blight.

Host
Degree of Susceptability
 
High
Moderately Susceptable
Moderately Resistant

Apple
Malus pumilla

Baldwin* Baldwin* Arkansas Black
  Barry Beacon* Ace Delicious
  Beacon* Belle de Boskoop Akane
  Ben Davis Blushing Golden Britemac
  Binet Rouge Cortland* Carroll
  Black Twig Discovery Cascade Spur Delicious
  Braeburn Delbarestival Classic Delicious
  Brown Snout Dutchess Cox’s Orange Pippin
  Burgundy Earligold* Dana Red Delicious
  Chisel Jersey Early McIntosh Dixi Red Delicious
  Cortland* Elstar Red Early McIntosh
  Dabinette Elstar* Early Red One McIntosh
  Durello di Forli Empire* Empire*
  Earli Jon Enterprise Enterprise*
  Earligold* Florinia Empire*
  Early Spur Rome Freedom* Freedom*
  Ellis Bitter Fulford Gala Goldrush
  Elstar* Gloster Gold Spur
  Fuji Gala* Haralson*
  Gala* Golden Delicious Jamba
  Geneva Early Granny Smith James Grieve
  Ginger Gold Gravenstein Holly Jonafree*
  Gloster 69 Grimes Golden Jonamac*
  Golden Delicious* Haralson* Honeygold
  Golden More Super Imperial Gala Keepsake*
  Golden Russet Jersymac Kidd’s Orange Red
  Granny Smith* Jonafree* Liberty*
  Hereford Redstreak Jonagold* Lurared
  Idared Jonamac* Lustre Elstar
  Jonafree* Julyred* Lysgolden
  Jonagold* Liberty* Macfree
  Jonathan Macoun Macspur
  Jonnee Maiden Blush Marshall McIntosh
  Kingston Black McIntosh Melba
  Late Harrison Minyon Melrose
  Lodi Missouri Pippon Mor Spur Mac
  Magog’s Redstreak Milton Northern Spy
  Margil Mollies Delicious Northwestern Greening
  Medaille d’Or Monroe* Nova Easygro
  Milwa Mutsu* Nured Delicious
  Monroe* Northern Spy Nured Winesap
  Mutsu* (Crispin) Novamac Ozark Gold
  Niagra Northern Spy Perfect Spur Criterion
  Nicobel Jonagold Pinova Pioneer Mac
  Nittany Prima* Prima*
  Northwest Greening* Puritan Priscilla
  Nured Jon Quinte* Quinte*
  Otava Red Cort Reanda
  Paulred Redfree [Red Free} Red Chief (Cambell) Delicious
  Pink Lady Red Fuji Red Chief (Mercier) Delicious
  Porter’s Perfection Red Fuji 4 Red Winesap
  Ramey York Reinette Grise du Redfree [Red Free]*
  Raritan Royal Gala* Red Max
  Red Fuji Nagano Rubinette Red Winesap
  Red Yorking Scotia

Regent

  Reglindis Sharon Remo
  Reine de Hatives Sir Prize* Rubinola
  Reine des Reinettes Smoothee* Scarlet Gala
  Rhode Island Greening Spartan Scarlet Spur Delicious
  Roberts crab Spijon Sir Prize*
  Rome Stark Gala Smoothee*
  Rome Beauty Starkspur Earlibase Stamared
  Royal Gala* Starr Stark Bounty
  Sampion Staybrite Stark Splendor
  Santana Summerred Starking Delicious
  Sir Prize* Summer Treat Starkrimson [Delicious]
  Somerset Redstreak Super Chief Red Delicious Starkspur Ultra Stripe Delicious
  Sops of Wine Topaz Starkspur Supreme Red Delicious
  Spigold Tydeman's Red Starkspur Compact Red Delicious
  Spur Gala Go Red Wayne* Stayman
  Starkspur Law Rome Wealthy* Sturdeespur Delicious
  Starr Winesap* Swiss Gormet (Arlet)
  Stembridge Jersey Virginiagold Top Spur Delicious
  Stokes Red   Turley
  Super Jon   Wellington
  Summer Rambo   Williams Pride
  Tremletts Bitter   Williams Red
  Twenty Ounce   Winesap*
  Ultra Red    
  Wayne*    
  White Jersey    
  Yellow Transparent    
  York Imperial    

Crabapple
(Malus
species)

Bechtel Brandywine Centurion
  Hyslop Dolgo Coralburst
  Mary Potter Hopa David
  Old Hope Indian Magic Evereste
  Ormiston Roy Kelsey Indian Summer
  Red Barron Red Splendor Prairie Fire
  Red Jade Snow Cloud Profusion
  Royalty Spring Snow Radiant
  Snowdrift Hilleri Red Vein Russian
  Strathmore Golden Hornet Thundercloud
  Transcendent Manchurian Vanguard
    Rosedale White Cascade
    Thunderchild  
Common Pear Abbe Fete Anjou Ayers
Pyrus communis Aurora Barlett* Beurre Bosc
  Bartlett* Comice* Bradford
  Bosc Coscia Carrick
  Clapp’s Favorite Dawn Harrow Delight
  Conference Douglas Harrow Sweet
  Comice* Duchess Harvest Queen*
  Flemish Beauty Ewart Honey Sweet
  Flordahome Garber Kieffer*
  Gorham Harvest Queen* Le Contet
  Hardenpont Kieffer* Lincoln*
  Hardy Lincoln* Luscious*
  Hood Luscious* Magness
  Oliver de Serres   Tyson
  Passe Crassane   Waite
  Red Bartlett   Warren
  Reimer Red   US 309
  Sheldon    
  Spaulding    
  Starkrimson    
  Williams    
  Winter Nallis    
Asian Pear
(Pyrus pyrifolia)
Hosui* Chojuro* Chojuro*
  Nijisseki (20th Century)* Hosui* Hosui*
    Nijisseki (20th Century)* Kosui
    Nijisseki (20th Century)* Kosui
      Shinseiki (New Century)*
*Degree of susceptability may vary in different locations.
Host
Degree of Susceptability
 
High
Moderately Susceptable
Moderately Resistant

Apple
Malus pumilla

Baldwin* Baldwin* Arkansas Black
  Barry Beacon* Ace Delicious
  Beacon* Belle de Boskoop Akane
  Ben Davis Blushing Golden Britemac
  Binet Rouge Cortland* Carroll
  Black Twig Discovery Cascade Spur Delicious
  Braeburn Delbarestival Classic Delicious
  Brown Snout Dutchess Cox’s Orange Pippin
  Burgundy Earligold* Dana Red Delicious
  Chisel Jersey Early McIntosh Dixi Red Delicious
  Cortland* Elstar Red Early McIntosh
  Dabinette Elstar* Early Red One McIntosh
  Durello di Forli Empire* Empire*
  Earli Jon Enterprise Enterprise*
  Earligold* Florinia Empire*
  Early Spur Rome Freedom* Freedom*
  Ellis Bitter Fulford Gala Goldrush
  Elstar* Gloster Gold Spur
  Fuji Gala* Haralson*
  Gala* Golden Delicious Jamba
  Geneva Early Granny Smith James Grieve
  Ginger Gold Gravenstein Holly Jonafree*
  Gloster 69 Grimes Golden Jonamac*
  Golden Delicious* Haralson* Honeygold
  Golden More Super Imperial Gala Keepsake*
  Golden Russet Jersymac Kidd’s Orange Red
  Granny Smith* Jonafree* Liberty*
  Hereford Redstreak Jonagold* Lurared
  Idared Jonamac* Lustre Elstar
  Jonafree* Julyred* Lysgolden
  Jonagold* Liberty* Macfree
  Jonathan Macoun Macspur
  Jonnee Maiden Blush Marshall McIntosh
  Kingston Black McIntosh Melba
  Late Harrison Minyon Melrose
  Lodi Missouri Pippon Mor Spur Mac
  Magog’s Redstreak Milton Northern Spy
  Margil Mollies Delicious Northwestern Greening
  Medaille d’Or Monroe* Nova Easygro
  Milwa Mutsu* Nured Delicious
  Monroe* Northern Spy Nured Winesap
  Mutsu* (Crispin) Novamac Ozark Gold
  Niagra Northern Spy Perfect Spur Criterion
  Nicobel Jonagold Pinova Pioneer Mac
  Nittany Prima* Prima*
  Northwest Greening* Puritan Priscilla
  Nured Jon Quinte* Quinte*
  Otava Red Cort Reanda
  Paulred Redfree [Red Free} Red Chief (Cambell) Delicious
  Pink Lady Red Fuji Red Chief (Mercier) Delicious
  Porter’s Perfection Red Fuji 4 Red Winesap
  Ramey York Reinette Grise du Redfree [Red Free]*
  Raritan Royal Gala* Red Max
  Red Fuji Nagano Rubinette Red Winesap
  Red Yorking Scotia

Regent

  Reglindis Sharon Remo
  Reine de Hatives Sir Prize* Rubinola
  Reine des Reinettes Smoothee* Scarlet Gala
  Rhode Island Greening Spartan Scarlet Spur Delicious
  Roberts crab Spijon Sir Prize*
  Rome Stark Gala Smoothee*
  Rome Beauty Starkspur Earlibase Stamared
  Royal Gala* Starr Stark Bounty
  Sampion Staybrite Stark Splendor
  Santana Summerred Starking Delicious
  Sir Prize* Summer Treat Starkrimson [Delicious]
  Somerset Redstreak Super Chief Red Delicious Starkspur Ultra Stripe Delicious
  Sops of Wine Topaz Starkspur Supreme Red Delicious
  Spigold Tydeman's Red Starkspur Compact Red Delicious
  Spur Gala Go Red Wayne* Stayman
  Starkspur Law Rome Wealthy* Sturdeespur Delicious
  Starr Winesap* Swiss Gormet (Arlet)
  Stembridge Jersey Virginiagold Top Spur Delicious
  Stokes Red   Turley
  Super Jon   Wellington
  Summer Rambo   Williams Pride
  Tremletts Bitter   Williams Red
  Twenty Ounce   Winesap*
  Ultra Red    
  Wayne*    
  White Jersey    
  Yellow Transparent    
  York Imperial    

Crabapple
(Malus
species)

Bechtel Brandywine Centurion
  Hyslop Dolgo Coralburst
  Mary Potter Hopa David
  Old Hope Indian Magic Evereste
  Ormiston Roy Kelsey Indian Summer
  Red Barron Red Splendor Prairie Fire
  Red Jade Snow Cloud Profusion
  Royalty Spring Snow Radiant
  Snowdrift Hilleri Red Vein Russian
  Strathmore Golden Hornet Thundercloud
  Transcendent Manchurian Vanguard
    Rosedale White Cascade
    Thunderchild  
Common Pear Abbe Fete Anjou Ayers
Pyrus communis Aurora Barlett* Beurre Bosc
  Bartlett* Comice* Bradford
  Bosc Coscia Carrick
  Clapp’s Favorite Dawn Harrow Delight
  Conference Douglas Harrow Sweet
  Comice* Duchess Harvest Queen*
  Flemish Beauty Ewart Honey Sweet
  Flordahome Garber Kieffer*
  Gorham Harvest Queen* Le Contet
  Hardenpont Kieffer* Lincoln*
  Hardy Lincoln* Luscious*
  Hood Luscious* Magness
  Oliver de Serres   Tyson
  Passe Crassane   Waite
  Red Bartlett   Warren
  Reimer Red   US 309
  Sheldon    
  Spaulding    
  Starkrimson    
  Williams    
  Winter Nallis    
Asian Pear
(Pyrus pyrifolia)
Hosui* Chojuro* Chojuro*
  Nijisseki (20th Century)* Hosui* Hosui*
    Nijisseki (20th Century)* Kosui
    Nijisseki (20th Century)* Kosui
      Shinseiki (New Century)*
*Degree of susceptability may vary in different locations.

Rootstocks of fruit trees also differ in susceptibility to fire blight (Table 2). Cultivars are usually grafted onto a different rootstock in order to control tree height, apple cultivars on dwarfing rootstocks usually begin bearing fruit at an earlier age compared to cultivars growing on their own rootstock.

Table 2: Susceptability of Apple and Pear Rootstocks to infection by Erwinia amylovora.


Host Rootstock Highly Susceptible Moderately Susceptible Moderately Resistant

Apple (Malus species)

Alnarp Malling 7 EMLA Bemali
  Malling 26 Budagovsky 9* Budagovsky 118
  Malling 9 Vineland 3 Budagovsky 490*
  Malling 26 Geneva 16 Geneva series
  Malling 27 Malling Merton 106 Malling 7
  Malling Merton 111 Malling Merton 111 Malling Merton 106
  Malling Merton 106   Malling Merton 111
  Mark Series   Robusta
  Ottawa   Vineyard 1
  Poland 2  

Vineyard 2

  Poland 16   Vineyard 5
  Poland 22   Vineyard 6
  Vineyard 4  

Vineyard 7

       
Pear (Pyrus species) Provence quince (Cydonia obonga)   Pyrus betulaefolia 'Old Home x Farmingdale'
  Pyrus communis ‘Bartlett’   Pyrus calleryana
  Pyrus communis 'Winter Nelis'   Pyrus communis ‘Old Home'
      Pyrus communis ‘Old Home X Farmingdale'

Additional Information:

Swift, C.E., Hammon, R., and Larsen, H.J. 2007. Backyard Orchard: Apples and Pears. Colorado State University Fact Sheet 2.800.

Jones, A.L. and Aldwinckle, H.S. (editors). 1990. Compendium of Apple and Pear Diseases. The American Phytopathological Society, 3340 Pilot Knob Rd., St. Paul, MN 55121.

Jones, A.L. and Sutton, T. B. 1996. Diseases of Tree Fruits in the East. North Central Regional Publication No. 45 (NCR 045). Available for $10 from Michigan State University, Bulletin Office, 10-B Agriculture Hall, East Lansing, MI, 48824-1039. This publication has excellent color photos.

Bessin, R.T., McManus, P.S., Brown, G.R. and Strang, J.G. (editors). Midwest Tree Fruit Pest Management Handbook.University of Kentucky.

Lewis, D., Domoto, P.A. and Gleason, M. (editors). 2009. Midwest Tree Fruit Spray Guide.

Durham, R.E., McNiel, R.E., Hartman, J.R., Potter, D.A., and Fountain, W.M. 1999. The Flowering Crabapple. University of Kentucky Publication ID-68. This publication contains an extensive list of crabapple cultivars and cultivar resistance to common diseases, including fire blight.

Beckerman, Janna. 2006. Disease Susceptibility of Common Apple Cultivars. Purdue University, Purdue Extension Publication BP-132-W. This publication contains an extensive list of apple and edible crabapple cultivars and cultivar susceptibility to common diseases, including fire blight.

1R.D. Koski, Colorado State University research associate; and W.R. Jacobi, professor; bioagricultural sciences and pest management. 7/98. Revised 10/09.

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