Fire Blight in Fruit Trees

Fire blight, bacterium Erwinia amylovora, is a destructive bacterial disease that attacks fruit bearing trees, largely apple, pear, and crabapple. It starts to manifest when trees begin active growth and when conditions are warm and moist. A watery liquid starts oozing from cankers, which are sores created by the bacteria in the previous year; this liquid is the bacteria spreading. Open flower to petal drop is when the tree is most susceptible to infection, causing damage that may be either localized or extensive, depending on the environmental conditions and plant health.

            The disease progresses from the end of the branch inward; dead fruit and leaves remain on the branch throughout the season, giving it the scorched look and the origin of the name “fire blight”. Infection can spread to the whole branch, trunk, and root system, eventually killing the whole plant. The splashing of rain, insect activity, and even honeybees pollinating can spread fire blight, which may be detrimental to an orchard over time. The pathogen responds to growing conditions. Unfortunately, high moisture and soil richness promote fire blight growth because the bacteria can spread faster in the plant when the host is healthy and happy.

When it spreads from the flower, fire blight streaks the wood under the bark with pink/red/orange tones (little flecks). This speckled appearance is a sign of the bacterial infection spreading in otherwise healthy-looking wood. The infection can be 2 or 3 feet away from the main damaged-looking wood, so when eradicating fire blight, be sure to check the wood color to confirm you are getting the extent of the contamination. The best time to cut the diseased wood out is in the late summer or winter when the bacteria isn’t growing. It is recommended to sanitize your shears/saws in between cuts as well. Spraying a special bactericide will stop the spread of the fire blight bacteria, but the diseased wood still needs to be removed.