Orchard to Determine
Fire Blight Risk
- By Deborah Breth
Cornell Cooperative Extension
• Will there be active cankers present in the orchard this year?
• Did you have fire blight in the orchards last year?
• Was there fire blight infection in the local area last year?
• Did you have fire blight in the local area two seasons ago?
• Are there any of your orchards or hosts in the local area where there was no fire blight in the last two seasons?
The risk of fire blight epidemics starting with blossom blight increases as you get closer to the source of fire blight infections in the area. The closer you are, the higher the risk, and the more stringent control measures must be planned and implemented.
The risk is also dependent on other factors specific to the orchard:
• Orchard age, vigor, and variety and rootstock susceptibility.
• Orchard size and ease of getting good spray coverage.
• Is it a high value orchard, or close to one?
Erwinia amylovora bacteria numbers have the capacity to double in 20 minutes at 70&Mac251;F. In 10 hours, one bacterium becomes one trillion bacteria. Therefore, the first step in planning for fire blight potential requires the reduction in the number and distribution of inoculum sources available for each phase of the disease (blossom blight, canker blight, shoot blight, “trauma” blight). If blossom blight is controlled, but canker blight is allowed to remain in the trees, the resulting oozing bacterial will be a source of infection for shoot blight the remainder of season.
Although eradication of the bacteria is impossible, steps for reducing inoculum sources will reduce the disease incidence. Remove wild hosts in hedgerows in surrounding areas, and neglected apple and pear orchards that are susceptible to fire blight.
Prune out cankers on an annual basis or remove whole trees if cankers are on the main trunk (or try canker surgery). The cankers with the indiscreet margins have the greatest potential for oozing in the spring. Prune while still dormant before bacteria become active and start to move within the tree cambium.
Canker removal will also serve to remove sources of black rot, white rot, and bitter rot that cause summer fruit rots.
Whole trees and large branches obviously need to be removed from the orchard for the above reasons, but smaller prunings can be raked to the row middles to chop with a flail mower in the spring.
If blossom blight is controlled but there is canker blight active in the orchard, there is still plenty of inoculum for shoot blight and trauma blight in the summer.
Maintain a balanced fertility program. Although nitrogen is known to help increase yields, it also results in greater susceptibility to fire blight. Copper sprays do not kill bacteria inside the cankers. It only reduces the efficiency of the bacteria oozing from the cankers to colonize the bark and bud surfaces during the prebloom period.
Additional benefits of early copper include:
• First scab protectant if applied before the first scab infection;
• Nutritional copper;
• Can be applied with oil (often recommended on copper labels as an adjuvant).
Results are not always consistent in improved control due to variables met with timing the application — control depends on how much copper remains on the tree surface relative to when cankers are oozing bacteria. Good spray coverage is critical.
Bacteria will colonize even non-susceptible varieties, so when applying copper to susceptible varieties in an orchard, you must apply copper to entire orchard. Early copper sprays do not eliminate the need to control blossom blight, copper just reduces the bacteria available to multiply during bloom.
The risk of phytotoxicity with copper increases as the tree phenology advances closer to bloom. Do not apply copper in fresh fruit varieties later than 1/4 inch green. Fruit russeting is likely on fresh fruit.
You also need to be ready for a fire blight outbreak during the season. Have some Streptomycin on hand. Remember that sunlight will break strip down. New packaging has increased the shelf life to two years.
The Fruit Growers News website offers a sampling of articles and features from each month. Subscribe to get all the news offered in The Fruit Growers News delivered right to you home!
Permission is granted for reprinting material, except for commercial or advertising purposes, provided The Fruit Growers News is given full credit.
- Copyright 2000 Great American Publishing, Inc.
- The Fruit Growers News
- 343 South Union Street - PO Box 128 - Sparta, MI 49345
- Phone 616-887-9008 - Fax 616-887-2666 - email
- All Rights Reserved
- The Fruit Growers News