What is Fire Blight?
Fire blight is a common disease that affects fruit trees, including pear and apple. The bacteria Erwinia amylovora causes the disease. Fire blight, named for the burned look of leaves on infected trees, destroys the tree’s fruit, leaves and branches. It can even kill more susceptible trees. Trees generally start to show symptoms in the spring. The bacteria enter the tree through new growth, like flowers and flower stems, and move up the branch turning leaves and fruit black. Once infected, the bacteria will live in the tree unless infected areas are removed.
How to Tell if Your Tree is Infected
When fire blight strikes a pear tree, abscesses form on the tree’s trunk and branches that ooze bacterial liquid on humid days. These lesions can leave large, dark streaks but usually they are small and easy to miss.
The more noticeable symptoms occur when leaves begin to shrivel, dieback and turn black. Dead leaves and fruit will remain on the tree throughout the season. Once the disease spreads from new growth to hardier wood, the wood beneath the bark will have reddish streaks. Eventually, the bacteria will make its way down to the roots.
How to Treat Fire Blight
Pear trees are highly susceptible to fire blight. Infected sections of the tree should be removed immediately. Extra caution should be taken to prevent spreading the bacteria. Dipping pruning shears in a 10% solution of bleach and water can help prevent the spread of the disease. The most important thing to do when removing infected tree tissue is to cut far enough below the lesions. Infected branches should be cut 12 inches below the lowest point of diseased tissue and then burned to prevent any new infection.
How to Prevent Fire Blight
The easiest way to prevent fire blight is to avoid planting highly susceptible trees. This includes most pear tree varieties, including Asian pears and red pears. Bradford Pears, the popular ornamental pear variety, are somewhat less susceptible but are still prone to fire blight infections. Certain apple varieties are also susceptible, such as Fuji, Granny Smith and Pink Lady.
Fire blight is driven by seasonal weather. When warmer temperatures are accompanied by wet weather, it creates the ideal condition for fire blight to develop. Since new growth is especially susceptible to fire blight, any activity that promotes new growth should be avoided. This includes ensuring that you are properly timing and applying nitrogen-based fertilizer and using proper pruning techniques.
Liquid copper can be effective at preventing fire blight when applied at the tip of a bud break. Application should continue every 4-5 days throughout the entire time the blossom is open. For pear trees, this may mean applying the liquid copper up to 12 times throughout the season. But be advised: this chemical application is not always effective and can also cause the skin of the pear fruit to scar. Timing of applications is critical for maximum effectiveness, but even properly timed and applied treatments are no guarantee that your fruit trees will remain fire blight-free.