| Fire Blight (Erwinia amylovora)
Fire blight, a destructive bacterial disease, causes much damage to apple, crabapple, hawthorn, mountain ash, pear, and occasionally cotoneaster and Saskatoons. It is especially noticeable in our cities and towns. One diseased tree may easily provide enough bacteria to infect susceptible trees within a 100-meter radius, and over time infect an entire neighborhood or an extensive farm orchard. Pollinating insects at blossoming time, plus sap-sucking insects, such as aphids and leafhoppers, are important carriers of the bacteria. The fire blight bacterium can only enter the plant through soft tissue, such as blossoms, young expanding leaves, and water sprouts, or through open wounds.
Blossoms may be the first indicator of the disease as they suddenly become blighted and turn brown. Alternatively, immediately after blossom drop, fruit clusters, twigs, and attached leaves may appear as if scorched by fire, hence the name fire blight. Infected leaves, twigs, and fruit sometimes remain on the trees all summer and well into the fall or winter. The bacteria tend to work their way downward into the larger branches killing patches of bark and thus forming cankers at the base of the diseased stem or branch. These cankers are discolored, slightly sunken, and tend to crack at their edges. If not removed, they may eventually encircle affected branches causing all parts above them to die. These cankers can carry bacteria over winter. In spring drops of ooze may emerge from the edge of the "hold-over" cankers, and the bacteria in the ooze may spread by insects, rain, wind, and pruning tools.
Prevention
If fire blight has been detected in your neighborhood, inspect your trees every few days starting at blossom time and until the blossoms naturally drop and the fruit begins to fill. Preventive measures are of critical importance and should be widely practiced:
1. Avoid susceptible varieties for new plantings (Check your seed catalogue for recommended cultivars and varieties).
2.Remove any known sources of infection on your property by destroying badly infected trees, and by pruning branches with light to moderate infections. Encourage your neighbors to do likewise.
3. Take measures directed at reducing sucking insect infestations wherever possible.
4.At pruning time, remove sprouts from the base of trees, and water shoots on the trunk and larger limbs. These soft growths may become easily infected if left on the trees. They provide ready access for the bacteria to trunks and larger limbs. Once the trunk is infected it may be impossible to save the tree.
5.Avoid excessive use of high nitrogen fertilizers as they promote soft susceptible growth.
6. For very valuable trees, blossom spraying with an antibiotic such as streptomycin sulphate can be used as a preventive measure. Caution is advised in areas where honeybees are present as the antibiotic can show up in the honey. Follow all recommendations on the container.
Control
Eradication is the chief means of control where fire blight is already heavily established. Light to moderate infections of the disease may be controlled by the prompt and conscientious application of the following practices:
1. In late fall, winter, or early spring, remove and burn all cankered limbs or seal them in plastic bags for garbage pick up. Where possible, make these cuts at least 15 — 30 cm (6 - 12 inches) or more, back along healthy wood. A thorough job at this time may alone be sufficient to control the disease in isolated trees.
2. During the growing season, cut off any infected twigs several inches below the Infection; but avoid excessive pruning at this time. Burn or seal cuttings in plastic bags for garbage pick up.
3. During pruning operations, disinfect the shears or pruning saw before beginning and after each successive cut. Disinfect tools with a solution such as Lysol (1 part to 500 parts of water), household bleach (1 tablespoon/pint of water), or a seventy per cent solution of denatured alcohol.
4. Subsequently, a Bordeaux mix of 1 part copper sulphate, 1 part hydrated lime, and 100 parts water may help to prevent infection of nearby healthy trees. The effectiveness is increased in spring if three sprayings are applied:
a. At early blossom stage, as buds are beginning to swell.
b. Full bloom, and
c. Late bloom, when blossoms are beginning to fall.
Spraying of isolated trees may be safely omitted if thorough eradication, as indicated above, is practiced.
Disclaimer
This web based publication may contain pesticide recommendations that are subject to change at any time. Therefore, these recommendations are provided as a guide only. It is always the pesticide applicator's responsibility, by law, to identify the pest and read and follow all current label directions for any pesticide being applied. Due to constantly changing labels and product registrations, some of the recommendations given may not be, or may no longer be legal in some jurisdictions. If any information in these recommendations disagrees with the label, the label directions must be followed explicitly. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. Gardenersweb assumes no liability resulting from the use of these recommendations. |
