Summer Fire Blight Management
The USU Pathology Lab tested the spread of fire blight through contaminated pruners, & found that 50% of the branches cut with the pruners became infected with fire blight. Symptoms included bacterial oozing (top), & wilting (bottom).
Most fire blight infections occur in spring from bacteria transmitted by bees to blossoms. But the bacteria can also be spread by water when it comes in contact with bacteria oozing from existing cankers and by using pruning tools. Bacterial infections from splashing water and pruning tools can occur year round. All the bacteria need is a tiny opening in the succulent leaf or twig tissue to enter the plant. Hail, strong winds, or even the act of pruning can wound the foliage, and bacteria splashed by water on leaves can enter through those wounds and cause new infections.
Some varieties, such as Fuji and Gala apples and Bartlett Pear, are more susceptible than others. On susceptible trees, the bacteria will move through the vascular tissue more quickly, from the infected shoot toward the main trunk. More and more of the branch will die as time progresses. Eventually, when the bacteria reach the trunk, the tree may die.
Correct pruning of infected shoots is an excellent way to reduce fire blight in an orchard. In the spring, removing infected shoots soon after the symptoms appear reduces dieback, as the bacteria will be stopped before they can move too far inside the branch. Since visible symptoms lag behind the advance of the bacteria, infected branches should be cut 12 inches beyond the visible dead shoot to remove all bacteria and stop the infection.
It is important to decontaminate the surface of pruning tools between cuts, using disinfecting wipes or dipping the blades in a 70% alcohol solution. In the USU plant pathology lab, we tested the effect of using disinfecting wipes on their ability to clean bacteria off tools and to prevent bacterial spread through pruning cuts. We sprayed the cleaning tools with a solution of fire blight bacteria, and found that the disinfecting wipes removed over 90% of the bacteria. To test spread of bacteria through contaminated pruning tools, we sprayed blades with a bacterial solution and cut into healthy branches. Almost 50% of the branches cut with contaminated blades became infected. None of the branches cut with clean blades did.
-Claudia Nischwitz, Plant Pathologist