![]() ![]() ![]() This continuous infection is an indication that the fire blight bacteria is systemic in the tree and will continue to express symptoms each year and serve as an infection source inoculating the orchard every year. Trees that show symptoms of fire blight for several years in a row should be removed. It is a good idea to walk through the orchard in the morning and evening so that the sun is in different positions in the sky and lights the tree from different angles. You often are looking up into the sun when pruning, so it is easy to miss a canker that you would have easily seen at another time of the day. It would have been easy for the grower to remove the fire blight in the early season because that year there was very little blossom blight and cutting it out early would have been worthwhile.Īfter you have made every effort to cut out fire blight, it is a good idea to walk through the orchard a few more times to look for cankers that were missed the first time. There was very little fire blight in that orchard in the spring. The grower had made an effort to remove all the cankers and I found very few cankers in the orchard that he and his pruning crew had missed. I was looking for cankers and wanted to document the beginning of oozing at bloom time. Several years ago I visited an orchard in the spring that had widespread fire blight the year before. This entire mess should have been removed with a cut between the cankerĪnd the trunk on the scaffold in the upper left. If the edge of the canker is well-defined on all sides, then growth of the canker stopped in the summer and the tree continued to grow after the canker stopped growing. If the canker margin is not well-defined, that indicates the canker was growing late in the season. I usually recommend at least 12 inches or to the next branch, whichever is more. If it looks like the canker has spread past the margin or the canker has a poorly defined margin, then you should cut off more. If the canker is well-defined, you can make the cut close to the edge of the canker. The walling off of a canker does tell you how far back to cut. While this is generally true, I have seen enough movement from old cankers that I don’t recommend leaving a canker even if you think they are walled off. It is commonly accepted that if the canker has a well-defined margin, the tree has walled off the infection and further movement is unlikely. The fire blight quickly kills young tissue and moves down the shoot to larger stems.Īll cankers should be cut out. These cankers are always associated with shoots that were killed last year. In old tissue, fire blight forms cankers, sunken areas on the trunk and shoots. During the growing season, fire blight spreads rapidly in young tissue. Often the leaves are still on in the early winter and the leaf stems usually remain until spring. The pruner should have taken this canker, not just cut off the infectedīranch leaving the canker behind to start the disease cycle again this spring.Īffected tissues are easy to recognize. I suggest you prune out all the visible symptoms of fire blight. Even if you do cut into wood that contains bacteria, their numbers are small and they can’t survive on the exposed surfaces of tools or pruning cuts. The disease is inactive because of the cold, so you won’t spread the disease with your pruning tools. Winter is the perfect time to remove fire blight. I believe that growers need to reduce fire blight when they can. Michigan State University Extension teaches that one of the keys to fire blight control is sanitation. There are antibiotics that most growers use during bloom to reduce the spread of this disease, but relying on antibiotic sprays at bloom and ignoring other culture practices to reduce the disease only sets you up for an unpleasant surprise if the antibiotic sprays fail due to timing, conditions or resistance. Ran down the branch at the lower right and into the base of these Bacterial ooze from overwintering cankers is the cause of infections during bloom.Ī fire blight canker is visible at the base of these shoots. Next year’s fire blight will come from trees that had active infections last year. That means the fireblight must come from trees that are already infected. Fire blight bacteria do not survive well outside the tree and do not overwinter outside of a host. The old canker was the source of the infection. If I get to the orchard early enough when the symptoms are just starting, I usually find shoot blight symptoms on a limb that has an old canker from last year. Often, fire blight strikes are localized in several areas in an orchard. I often wonder where fire blight comes from in the spring. ![]()
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