Fire Blight on Pears and Indian Hawthorn in North Florida and South Georgia

By: Dr. Tim Momol, Department of Plant Pathology, University of Florida - IFAS

Florida Extension faculty from Bay, Holmes, Washington, Jefferson, Leon and Suwannee counties and other horticultural scientists from north Florida are reporting unusually high fire blight occurrences this spring (2000). Reported hosts with fire blight-like symptoms are "Bradford" and "Aristocrat" Pears and Indian Hawthorn (Including South Georgia).

Fruit spurs on pear with fire blight infected blossoms (Photograph by A. L. Jones, Michigan State University)Florida Extension Plant Diagnostic Clinic (FEPDC) at NFREC, Quincy received both DDIS samples (digital images) and biological (traditional) samples. Based on symptoms (digital and traditional), and colony morphology of the bacteria on MMS medium and PCR analysis (molecular identification technique), we confirmed the presence of Erwinia amylovora (causal agent of fire blight) from all biological samples that were sent to us from Florida and Georgia. Rain (especially wind-driven) along with temperatures between 65-85 F during bloom period, is ideal for blossom blight infections. Extended spring and the ideal conditions for fire blight development that we are experiencing may explain this outbreak.

There are other diseases on woody plants with symptoms resembling fire blight such as, Botryospaeria canker, pear blast, and Nectria twig blight. If you need accurate diagnosis contact nearest Florida Extension in your county or FEPDC at NFREC, Quincy, FL.

In the landscape, ornamental pears (Bradford) and other host plants are usually not highly susceptible to fire blight infections. Especially older plants will survive the attack of fire blight. Our recommendation for older plants in the landscape is to delay pruning until next winter (dormant period). It is necessary to prune infected tissues and cankers during dormant period and apply copper based compounds next spring at the green tip stage or few weeks before flowering.

Pruning after infections during spring and summer is debatable. If you decide to do pruning at the actively growing stage of plant, this is the relevant information: "Removing sources of infection: Beginning about one week after petal fall, monitor the orchard to locate blighted limbs for removal. For the greatest effect on the current season's damage severity, infected limbs should be removed as soon as early symptoms are detected and before extensive necrosis develops. Where the number and distribution of strikes is too great for removal within a few days, it may be best to leave most strikes and cut out only those that threaten the main stem. On young trees, and those on dwarfing rootstocks, early strikes in the tops of the trees often provide inoculum for later infections of shoots and sprouts on lower limbs near the trunk, which may result in tree loss. Give these early strikes in the tops of trees a high priority for removal. Do not combine the practices of fire blight removal with pruning and training of young, high-density trees" (by P.W. Steiner (, University of Maryland, and A. R. Biggs, West Virginia University, 1998.

"Cutting out active infections is often viewed quite skeptically as being an impossible job that requires much labor and often seems to be ineffective. In truth, this practice can be extremely effective in limiting the number and distribution of secondary canker and shoot infections as well as reducing the risks for serious damage following summer (for Florida late spring) hail and wind storms. To be really effective, cutting operations need to begin as soon as early symptoms appear. In addition, it is absolutely imperative that all cuts be made using the "ugly stub" approach in which cuts are always made into wood that is at least 2 years old to take advantage of natural physiological resistance expressed even in susceptible varieties. It has also been shown that there is no advantage to be gained by following the old recommendation of surface sterilizing cutting tools between each cut. The "ugly stub" method acknowledges the fact that the bacteria are systemic and can be several feet to yards ahead of any visible symptoms so that any cutting wounds provide an excellent opportunity for the resident bacteria to colonized and quickly establish a small canker around the cut. When cuts are made in the traditional fashion, flush with the next healthy branch union, many of these cankers will remain in the orchard to fuel next year's epidemic. Cutting back to a 4- to 6-inch naked stub does not prevent the formation of small cankers, but their position is now such that the stubs and the canker can be safely and completely removed during the regular dormant pruning operation. Simply spray-painting these stubs makes them easier to find when the trees are dormant. The primary purpose of this cutting effort is to reduce the number and distribution of secondary sources of inoculum that can fuel a continuing epidemic of shoot blight through the season. Two factors are important in obtaining maximum effect: the cutting must begin promptly when early symptoms first appear; the cut material must be removed from the orchard; the cuts must be made following the ugly stub procedure; such cutting must be done every year, even when the overall amount of blight is very low" by Paul W. Steiner, Professor & Extension Fruit Pathologist Department of Natural Resource Sciences, University of Maryland, College Park, MD 20742. (Presented at the State Horticultural Association of Pennsylvania Annual Meeting, January 2000)

Commercial growers and nurseries should consult their county extension agents or use UF/IFAS recommendations in Florida. If you need further information on fire blight send e-mail to Tim Momol (

MARYBLYTTM is a predictive computer program for forecasting fire blight disease in apples and pears. This tool is useful for judging when to spray bactericides against blossom infections. MARYBLYTTM can be purchased from Gempler's, Inc. (800-382-8473).

Related Sites from Internet:

Fire blight of apple and pear

Principles of Fire Blight Control in the Pacific Northwest