Bill Starr: Watch out for signs of fire blight

Published 7:02 am Sunday, May 21, 2017

There are lots of phrases in the English language that include the word “fire.” For example, “don’t play with ____ unless you want to get burned,” “liar liar pants on ____.” “Where there is smoke, there is ___.” “Earth, wind and ___.” Of course, the answer to all those phrases is fire. But I have been seeing some problems in pear and apple trees that also include the word fire: fire blight to be more specific. I have seen this disease in numerous pear trees mostly, throughout the county. I have seen it in fruit-producing pear trees as well as ornamental pears.
Fire blight is a disease caused by the bacteria Erwinia amylovia, it is a common disease of pear and apple trees as well as other members of the rose family. Badly diseased trees can be disfigured and even killed by this disease. The term fire blight describes the blackened, burnt appearance of damaged flowers, twigs, and foliage. Symptoms usually appear in early spring and quite often go unnoticed until they become severe. When the blossoms first appear, they will quickly wilt and finally turn brown, shortly after the blossoms die, and the leaves on the same spur or shoot turn brown on apple trees or black on pear trees. The ends of the branches tend to turn black as well. As the twig and leaf blight progresses, leaves die and curl downward. The tips of the blighted twigs, shoots, and sprouts start to droop, producing the typical shepherd’s crook. This is usually when most people notice this disease. If the disease continues to develop you will eventually see an amber colored, oozing discharge near the blight affected areas on the tree. Typically, you will see this gummy amber colored discharge during warm, humid weather like we are experiencing right now. Susceptibility to fire blight depends on the variety or cultivar of the apple or pear tree, the weather conditions and the maturity of the tissue. Succulent new growth is very vulnerable to the disease. Mature apple and pear tissues are much more resistant to infection than young tissues.
So how do control this disease? No single practice can insure complete control of fire blight; however, using a combination of control techniques can help to reduce the disease. Optimally if any pruning is required to remove diseased portions of the tree it should be done in the winter when the tree is dormant as there is less chance of spreading fire blight on the cutting tools. Sometimes the disease can be so severe that immediate pruning is necessary to prevent the disease from reaching the main trunk. If pruning is performed in the spring or summer it is important to prune 8-12 inches below the infected tissue, and most importantly you should sterilize the cutting tools with either an alcohol or bleach solution after each cut is made.
Chemical control, the most effective chemical control of fire blight is achieved by the application of streptomycin during bloom. Because blossoms open over a period of several days, three to four applications during bloom are necessary. Apply the first bloom spray shortly after the first blossoms open. A second spray is applied when about half of the blossoms that were not open during the first spray do open. A third spray should be applied when the remaining blossoms open (full bloom). Additional sprays may be needed if the bloom period is unusually long. When using streptomycin, start as soon as blooming begins, because it is ineffective or not as effective once infection begins. For best results use late afternoon or early evening because streptomycin starts to break down in sunlight. Do not use streptomycin after bloom, except within 24 hours after a hail storm. Excessive use of streptomycin may result in the development of resistant strains of the fire blight bacterium. Follow all label instructions regarding amounts of pesticide to use, method of application, and safety warnings. Another chemical option is to use copper hydroxide, copper containing fungicides for control, but be careful because some of these copper fungicides can be phytotoxic to crabapple trees.
Fire blight seems to be prevalent this year at least from the calls I have been receiving about this disease. Treatment of the disease this time of the year might be a little too late, but if you think your apple or pear trees may have fire blight, please feel free to contact our office for verification if you need to. Just think about all the references to fire in our everyday phrases and songs. I fell into a burning ring of ____. I went down, down, down, and the flames went higher. Fire blight that is!
Bill Starr is Sumter County Extension coordinator/ag agent, University of Georgia Cooperative Extension Service. Contact him at 229-924-4476.