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Fact Sheet No. 2.907 Gardening Series|Diseases by R.D. Koski and W.R. Jacobi * Fire blight is a bacterial disease that affects bodies, and inadvertently carry the Quick Facts certain in the rose family (). to opening blossoms. Bacterial ooze splashed It is especially destructive to ( by can also spread the pathogen. • Fire blight is a bacterial spp.), (Pyrus spp.), and crabapples Once in the blossom, bacteria multiply disease that can kill branches (Malus spp.). The disease also can occur on rapidly in the nectar and eventually enter the and whole plants of many serviceberries ( spp.), flowering flower tissue. From the flower, the bacteria members of the rose family, (Chaenolmeles spp.), move into the branch. When the bacteria including , , ( spp.), hawthorns ( invade and kill the cambial tissue of the and crabapple. spp.), quinces (Cydonia spp.), branch, all flowers, leaves and fruit above the ( spp.), blackberries (Rubus spp.), girdled area die. • Symptoms include dead (Rubus spp.), and mountain ashes also can take place through branches, water-soaked (Sorbus spp.). natural openings in leaves (stomata), blossoms, light brown to Disease incidence varies from year to branches (), pruning wounds, blackened leaves, discolored year and severity is influenced by feeding and ovipositing, and . Droplets of bark, black “shepherd’s susceptibility, tree age, succulence of tissues bacterial ooze can form on twigs within three crook” twigs, and dried fruits. and spring meteorological conditions. days after infection. The disease is most serious when spring • Fire blight bacteria can be temperatures during pre-bloom and bloom spread by , splashing Diagnosis are warmer than average. Warm rainy springs rain or contaminated pruning are particularly conducive to rapid spread Symptoms of fire blight are first seen tools. of the pathogen, resulting in blossom blight. about the time of petal fall. Infected blossoms Blight of twig terminals can occur in late May appear water-soaked and wilt rapidly • Management includes through June during driven rain events. before turning dark brown; this phase of resistant varieties, cultural Hail and wind damage provide wounds that the disease is referred to as blossom blight. practices, pruning and allow the pathogen to enter at other times. As the bacterial invasion progresses, leaves preventive chemical sprays. Hot summer generally slows or stops wilt, darken and remain attached to the tree • Always follow label directions the disease. (Figure 2); this gives the tree a fire-scorched appearance, thus the name “fire blight.” for any pesticide. For updated Infected twigs darken and branch tips spray rates and related Disease Cycle may bend over forming a “shepherd’s crook.” information, consult the Fire blight is caused by the bacterium During wet conditions infected tissue may Midwest Tree Fruit Spray amylovora. The bacteria overwinter exude creamy bacterial ooze in droplets or Guide, your State in blighted branches and at the edge of fine, hair-like strands. Infected fruits also University Extension county cankers (areas of bark killed by bacteria) exude bacterial ooze. Rather than dropping office and other resources. (Figure 1). In spring, when temperatures from the tree, infected fruits gradually dry frequently reach 65 F, the bacteria and remain attached to the branch. multiply rapidly. Fire blight cankers on branches or stems Masses of bacteria are forced through appear as dark discolored areas that are cracks and bark pores to the bark surface, slightly sunken, with a narrow callus ridge where they form a sweet, gummy exudate along the outer edge (Figure 3). The narrow called bacterial ooze. Insects such as aphids, callus ridge is diagnostic for differentiating ants, bees, beetles, and flies, are attracted fire blight cankers from fungal cankers. ©Colorado State University to this ooze, pick up the bacteria on their Under the bark associated with a canker, the Extension. 7/98. Revised 12/14. inner bark turns from green to brown, but www.ext.colostate.edu the appearance varies depending on plant * R.D. Koski, Colorado State University research variety. Droplets of bacterial ooze may appear associate; and W.R. Jacobi, retired professor; bioagricultural sciences and pest management. 12/2014 on the canker. Figure 2: Blighted leaves on ornamental apple.

Figure 1: Fire blight life cycle. Figure 3: Sunken black canker on apple branch.

Disease Management Avoid blight susceptible apple rootstocks each cut, surface sterilize all tools used in There is no cure for this disease, so especially when grafted to susceptible pruning. Dip tools in household bleach prevention is the best solution for the scions (Table 2). To minimize stress that or ethyl alcohol, or use household spray management of fire blight. Fire blight may predispose the tree to other disease- disinfectants. Spreading the blight bacteria management methods include: planting causing agents, select varieties adapted to risk is lowered if pruning is delayed until resistant varieties, implementing cultural the growing area. Local weather conditions mid winter. Winter pruning can also be practices that favor growth of the plant from year to year also affect the amount of accomplished more efficiently because rather than the pathogen, pruning fire blight found in a variety. pruning tools need not be disinfected to remove infected plant parts, and Cultural practices: Minimizing rapid between cuts if pruning is done when trees chemical sprays. Using resistant varieties growth and succulent tissue will reduce are fully dormant. To decrease the chance is the most effective prevention method. the risk of fire blight developing on the of new , promptly remove from Spraying chemicals is not recommended susceptible young, succulent tissue. Annual the site and destroy all infected branches. for homeowners because of chemical pruning with avoidance of cuts will To remove a canker that does not availability, potential phytoxicity and the help minimize tree vigor. Similarly, limiting extend more than 50 percent around a large critical timing of sprays. the amount of nitrogen fertilizer will reduce stem, first make a cut through the bark Resistant varieties: of apple, twig terminal growth. Fertilization should down to the 1 to 2 inches outside the crabapple, and pear differ in their degree be based on the results of foliar and/or soil canker margin. The cut should not have of susceptibility to the bacterium (Table 1) nutrient analysis and should not be applied any sharp angles. Next, cut and scrape although some cultivars are less susceptible in excess. away all infected bark down to the wood. than others, no cultivar is immune to Pruning: Remove all blighted twigs Treat exposed wounds with a 70 percent infection when the pathogen is abundant and cankered branches. Prune twigs and alcohol solution. The whole stem should be and conditions are favorable for infection. branches 8 to 12 inches below the edge removed if a canker extends around more of visible infection. CAUTION! After than 50 percent of the stem. During pruning, take care to avoid Table 1. Varietal susceptibility to fire blight. unnecessary wounds to the tree. When Degree of Susceptibility climbing trees, wear soft-soled shoes to Highly Moderately Moderately prevent bark injuries. Host Susceptible Susceptible Resistant Remove fire blight infected branches Apple * Baldwin* during summer if one or more of the Malus pumila Barry * Ace Delicious following conditions exist: • Infections are in young, vigorous trees Beacon* and the bacteria may girdle the main Blushing Golden Britemac stem or main branches. Binet Rouge * Carroll • Infections are in dwarfing trees on Black Twig Cascade Spur Delicious highly sensitive rootstocks, such as M.9 Delbarestival Classic Delicious or M.26. Dutchess Cox’s Orange Pippin • The number of infections in older trees is limited and can easily be removed. Burgundy Earligold* Dana • It is a dry, sunny day when there is no Early McIntosh Dixi Red Delicious chance of rain for 48 hours. Cortland* Red Early McIntosh Chemical sprays: Chemical sprays are Dabinette Elstar* Early Red One Delicious preventive treatments that must be applied Durello di Forli * Empire* prior to the onset of fire blight symptoms; sprays have little effect after the onset of Earli Jon * Enterprise* symptoms. Expect blossom infections Earligold* Florinia Empire* and plan to apply chemical sprays if: Early Spur Rome Freedom* Freedom* temperatures remain between 65 F and 86 Fulford Goldrush F for a day or more during flower bloom, Elstar* Gloster Gold Spur there is at least a trace of rainfall, the Gala* * relative humidity remains above 60 percent for 24 hours, there is abundant succulent Gala* Jamba shoot growth, or there are fruit injuries Geneva Early from hail or other agents. For specific Holly Jonafree* instruction on sprays and timing please Gloster 69 Jonamac* use the Midwest Tree Fruit Spray Guide at Golden Delicious* Haralson* https://extension.entm.purdue.edu/ Golden More Super Imperial Gala Keepsake publications/PM1282-1.pdf. The chemicals may be sold on various trade names. Jersymac Kidd’s Orange Red Streptomycin is an antibiotic that Granny Smith* Jonafree* * is acceptable for use to protect trees but Hereford * Lurared may be difficult to obtain. Do not use Jonamac Lustre Elstar streptomycin after symptom development Jonafree* Julyred Lysgolden since it may lead to antibiotic resistance in Jonagold* Liberty* Macfree the bacterial population. Aluminum tris is a bactericide used Macoun Macspur prior to and during bloom. Jonnee Maiden Blush Marshall McIntosh Copper sprays are toxic to many McIntosh species of bacteria. Copper sprays are best Late Harrison Minyon used during dormancy and prior to bud Missouri Pippin Mor Spur Mac break because they may damage leaves and young fruit. Do not apply sprays Magog’s Restreak Milton within 50 days of apple harvest or within Margil Mollies Delicious Northwestern Greening 30 days of pear harvest. Do not mix with Medaille d’Or Monroe* Nova Easygro oils or phytotoxicity issues can occur. Milwa * Nured Delicious Copper is available in several forms and Monroe* Northern Spy Nured sold under various trade names, including Mutsu* (Crispin) Novamac Ozark Gold 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 (Continued) ways that are not favorable for infection Table 1. Varietal susceptibility to fire blight. by E. amylovora. The length of time that shoot growth is inhibited depends Degree of Susceptibility on the application rate and tree vigor. Highly Moderately Moderately Prohexadione-calcium is ineffective for Host Susceptible Susceptible Resistant control of the blossom blight phase of Apple Niagra Northern Spy Perfect Spur Criterion fire blight. Malus pumila (continued) Nicobel Jonagold Pioneer Mac Nittany Prima* Prima* Additional Information Northwest Greening* Puritan Priscilla Swift, C.E., Hammon, R., and Larsen, H.J. Nured Jon Quinte* Quinte* 2007. Backyard Orchard: Apples and Otava Red Cort Reanda Pears. Colorado State University Fact Paulred Redfree [Red Free]* Red Chief (Campbell) Sheet 2.800. Available online at: www. Delicious ext.colostate.edu/pubs/garden/02800. Pink Lady Red Fuji Red Chief (Mercier) html. Delicious Jones, A.L. and Aldwinckle, H.S. Porter’s Perfection Red Fuji 4 Red Winesap (editors). 1990. Compendium of Apple Ramey York Grise du Redfree [Red Free]* and Pear Diseases. The American Raritan Royal Gala* Red Max Phytopathological Society, 3340 Pilot Red Fuji Nagano Rubinette Red Winesap Knob Rd., St. Paul, MN 55121. Jones, A.L. and Sutton, T. B. 1996. Diseases Red Yorking Scotia Regent of Tree Fruits in the East. North Central Reglindis Sharon Remo Regional Publication No. 45 (NCR Reine de Hatives Sir Prize* Rubinola 045) Available for $10 from Reine des Reinettes Smoothee* Scarlet Gala State University, Bulletin Office, 10-B Scarlet Spur Delicious Agriculture Hall, East Lansing, MI, Roberts crab Spijon Sir Prize* 48824-1039 (http://web2.msue.msu. edu/bulletins/intro.cfm)This publication Rome Stark Gala Smoothee* has excellent color photos. Rome Beauty Starkspur Earliblase Stamared Bessin, R.T., McManus, P.S., Brown, G.R. Royal Gala* Starr Stark Bounty and Strang, J.G. (editors). Midwest Tree Sampion Staybrite Stark Splendor Fruit Pest Management Handbook. Santana Summerred Starking Delicious University of Kentucky. Available online Sir Prize* Summer Treat Starkrimson [Delicious] at: www.ca.uky.edu/agc/pubs/id/id93/ id93.htm. Sommerset Redstreak* Super Chief Red Starkspur Ultra Stripe Delicious Delicious Lewis, D., Domoto, P.A. and Gleason, M. (editors). 2009. Midwest Tree Fruit Sops of Starkspur Supreme Red Delicious Spray Guide. Available online at: www. Spigold Tydeman’s Red Starkspur Compact Red extension.iastate.edu/publications/ Delicious pm1282.pdf. Spur Gala Go Red Wayne* Durham, R.E., McNiel, R.E., Hartman, J.R., Potter, D.A., and Fountain, W.M. 1999. Starkspur Law Rome * Sturdeespur Delicious The Flowering Crabapple. University of Starr Winesap* Swiss Gormet (Arlet) Kentucky Publication ID-68. Available Stembridge Jersey Virginiagold Top Spur Delicious online at: www.ca.uky.edu/agc/pubs/id/ Stokes Red Turley id68/id68.pdf. This publication contains Sun Fuji Viking an extensive list of crabapple cultivars Super Jon Wellington and cultivar resistance to common diseases, including fire blight. Summer Rambo Williams Pride Beckerman, Janna. 2006. Disease Tremletts Bitter Williams Red Susceptibility of Common Apple Twenty Ounce Winesap* Cultivars. Purdue University, Purdue Ultra Red Jonathan Extension Publication BP-132-W. Wayne* Available online at: www.ces.purdue. White Jersey edu/extmedia/BP/BP-132-W.pdf. This publication contains an extensive list Yellow Transparent of apple and edible crabapple cultivars and cultivar susceptibility to common diseases, including fire blight. (Continued) Table 1. Varietal susceptibility to fire blight.

Degree of Susceptibility Highly Moderately Moderately Host Susceptible Susceptible Resistant Crabapple Bechtel Brandywine Centurion (Malus species) 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 () Aurora Bartlett* Beurre Bosc Bartlett* Comice* Bradford Bosc Coscia Carrick Capp’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 Max-Red Bartlett Maxine* Maxine* Oliver de Serres Red Rogue* Moonglow [Moon Glow] Passe Crassane Seckel Montgomery Red Bartlett Sparklett Old Home Reimer Red Worden Seckel* Orient Sheldon Potomac Spalding Starking Delicious Starkrimson Tyson Williams Waite Winter Nallis Warren Asian Pear Hosui* Chojuro* Chojuro* (Pyrus pyrifolia) Nijisseki (20th Century)* Hosui* Hosui* Nijisseki Kosui (20th Century)* Shinseiki Shinko (New Century)* Shinseiki (New Century)* *Degree of susceptibility 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. Susceptibility of Apple Rootstocks to infection by Erwinia amylovora. Highly Moderately Moderately Host Rootstock Susceptible Susceptible Resistant Apple Alnarp Malling 7 EMLA Bemali (Malus species) 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 3 Vineyard 1 Poland 2 Vineyard 2 Poland 16 Vineyard 5 Poland 22 Vineyard 6 Vineyard 4 Vineyard 7 Pear Provence quince Pyrus betulaefolia ‘Old (Pyrus species) (Cydonia obonga) Home X Farmingdale’ Pyrus communis ‘Bartlett’ Pyrus communis Pyrus communis ‘Old Home’ ‘Winter Nelis’ Pyrus communis ‘Old Home X Farmingdale

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