Jasper County
Fire Blight in Fruit Trees
Fireblight is a bacterial disease affecting apples, pears, hawthorne, pyracantha, quince and related species. The bacteria live over winter in cankers or diseased areas of the tree. The bacteria is spread by insects, birds, wind, and rain. Sometimes careless pruning practices will spread the bacteria.
There are several symptoms of fireblight on a plant. These are:
Blossom blight: The blossoms are the first part of the plant to become infected in the spring. This is partly due to the attractiveness of blossoms to insects which spread the bacteria. Infected blossoms turn brown and die with the flower parts remaining attached.
Shoot or terminal blight: New shoot growth is susceptible to infection in spring and early summer. Infected tips wilt then die and assume a characteristic "shepherd’s crook" appearance. The dead leaves remain attached to the dried shoots and may kill a foot or more of terminal growth.
Cankers: Fireblight cankers (a diseased area) can develop on limbs and even trunks of trees. This bacteria can colonize in an area where the bark has been wounded (pruning, hail damage, mower or mechanical damage, etc.) The infected area will become discolored and sunken. Fire blight cankers will ooze a sticky substance. This sticky ooze is high in sugar that attracts insects and birds to aid in the spread of fireblight.
Control of fireblight:
Resistant varieties: Varieties such as Red Delicious, Golden Delicious, Liberty, Jonafree are some of the resistant apples. Kieffer, Sheckel, Dutchess and Maxine are some of the resistant varieties of pears. Unfortunately there are little choices available in hawthorne and pyracantha species.
Pruning: Since fireblight over winters in plant parts, the removal of these parts can reduce the severity of the disease the next year. Waiting until winter to prune is sometimes not desirable because the infected areas are not as visible as when foliage is present. A pruning in August after leaf growth has stopped would be advisable because affected areas can be easily identified. Do not attempt to prune infected shoots in the spring, this will only spread the bacteria to other parts of the tree. When pruning make cuts 8 to 12 inches below infected areas to ensure removal of diseased wood. Always disinfect tools between cuts.
Fertilization: Fireblight is most prevalent on vigorously growing trees. For this reason applying high nitrogen fertilizers should be limited or carefully controlled. Apply a balanced fertilizer (8-8-8, 12-12-12, etc.) in September to November. Remember trees planted in your yard will be affected by fertilizers applied to your lawn!
Chemical control: The use of streptomycin, an antibiotic, can be used to control fireblight. Spraying should begin with a dormant spray of Bordeaux, lime-sulphur, and herbicidal oil followed by 4 sprays of streptomycin at pink bud, 10% open blossoms, full bloom, and at petal fall. Read and follow label instructions.
Fireblight disease runs in cycles, the disease may be severe some years and show little or no damage other years. It is most severe during wet springs at temperatures of 60 to 75° F.
For more information contact the University of Missouri Extension Center and request MU Guides: 6020, Fireblight; G6022, Apple Varieties; and G6010, Spray Schedule for Homeowners.
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University of Missouri Extension Jasper County jasperco@missouri.edu Web site maintained by: Virginia Bryan bryanv@missouri.edu Last updated: 09/02/2009 |
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