Extension Circular 55-1814: This  is about fire blight of apples and pears.  Includes symptoms, cause, control, and resistant and susceptible varieties

Weihing, John L.

Whitney, Wayne C.

English

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnHistorical Materials from University of Nebraska-Lincoln Extension Extension4-1955EC55-1814 Fire Blight of Apples and PearsJohn L. WeihingWayne C. 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, John L. and Whitney, Wayne C., "EC55-1814 Fire Blight of Apples and Pears" (1955). Historical Materials from University ofNebraska-Lincoln Extension. 3260.http://digitalcommons.unl.edu/extensionhist/3260EXTENSION SERVICE UNIVERSITY OF NEBRASKA COLLEGE OF AGRICULTURE AND U.S. DEPARTMENT OF AGRICULTURE COOPERATING W. V . LAMBERT, DIRECTOR FIRE BLIGHT OF APPLES AND PEARS. John L. Weihing and Wayne C. Whitney 1 SYMPTOMS Fire blight may attack blossoms, fruits, leaves, twigs, branches and the trunks of apple and pear trees. Infected blossoms wilt, turn brown and die. Usually infected leaves are killed entirely, but occasionally only a portion will show infection. Affected portions turn various shades of brown and die. The leaves killed by fire blight remain on the twigs for long periods. Twig infection maybe so common that an affected tree will appear to have been scorched by fire. Also, leaves on affected branches may show premature fall colora-tion. Infection of branches and trunks results in the de-velopment of cankers. On the branches many of the cankers are found on the under ·side. At first the cankers are light brown in color ·and as they age the bark cracks and the canker surface becomes depressed. They may ~ontinue to enlarge until they girdle the branch or trunk, in which case the part above the girdle dies. CAUSE Fire b 1 i gh t is caused by a bacterial organism (Erwinia amylovora). The causal organism may over-winter 1n infected twigs or at the borders of branch and trunk cankers. In the spring the bacteria begin multiplying rapidly and many are forced to the outside of the wood through cracks or natural openings. Once outside they may be distributed by wind, rain, and insects. However, moisture is necessary for the bacteria to be able to survive and initiate infection. Consequently fire blight infection occurs during periods of high humidity, and blight in epidemic proportions is noticed after periods of rainy weather. 1 Extension Plant Pathologifit and Extension Horticul-turist, respectively. CONTROL -3-Past recomm.endations for control of fire blight have been eradication of diseased wood, and the plant-ing of resistant varieties. Rapidly growing twigs which have been stimulated by excessive fertility or heavy pruning are extremely susceptible to fire blight. It is advisable, therefore, to retard excessive twig growth by reducing the amount of nitrogenous fertilizer appli-cations, and very light pruning. Sod culture also tends to reduce over-vigorous growth. Since the fire blight bacteria overwinter in the cankers and possibly in the small twigs, it is advisable to remove and destroy infected parts when the tree is dormant. When removing a diseased branch the cut should be made 4 to 5 inches below any visible signs of the disease. Where a main branch is diseased, cut back to a strong, horizontal, outward-growing branch. The wounds should be painted with a standard wound dressing such as Bordeaux paint, asphaltum, 1 e ad paint, or pruning compound. Cankers on main limbs or on the trunk can be re-moved by surgical methods. The cut in the bark should be made about 2 inches outside of the margin of the canker and all of the diseased bark removed. The in-struments used for removal of a canker should be dipped in a disinfectant such as alcohol or chlorox be-fore going to another canker. The wounds should be treated with a standard wound dressing. Recent studies have shown that good fire blight control can be obtained by spraying trees during early bloom, full bloom, ·and petal fall with some of the anti-biotic materials used in human medicine, principally streptomycin and terramycin. Commercial antibiotic preparations for orchard use will be available in the near future. Instructions regarding their use will be on or in the containers. Spraying for fire blight control is relatively new and is a big advancement in the con-trol of this disease. -4-RESIST ANT AND SUSCEPTIBLE VARIETIES Apple and pear varieties differ in their suscepti-bility to fire blight. Following is a list of the more widely grown varieties of apples and pears classified according to their degree of susceptibility. Apple Varieties Pear Varieties Highly Susceptible Jonathan Minjon Secor Yellow Transparent Susceptible Beacon Cortland Prairie Spy Wealthy Resistant Duchess Early Mcintosh Grimes Golden Delicious Haralson King David Missouri Pippin Turley Sharon . Bartlett Clapp's Favorite Flemish Beauty Patten Garber Douglas Seckel Kieffer Highly Resistant Delicious Northwestern Greening Winesap 

EC55-1814  Fire Blight of Apples and Pears

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=4269&amp;context=extensionhist

EC55-1814 Fire Blight of Apples and Pears

Abstract

Similar works

Full text

Available Versions

DigitalCommons@University of Nebraska