Have you noticed scorched leaves, twigs and branches on your crabapple? Or a strange curl at the branch tips? It could be Fire blight a bacterial disease caused by Erwinia amylovora. Fire blight can affect some of our favorite street & fruit trees – apple, pear, crabapple, quince, serviceberry and hawthorn.
Symptoms of Fire blight include dead branches, blackened leaves, dried fruit and shepard’s hook. The flowers usually show the first symptoms of Fire blight, looking wilted and eventually turning dark brown. The disease attacks the new growth on the tips of trees first, traveling down the branch toward the roots. As the branch dies, it curls at the end creating a shepard’s hook (a telltale sign of Fire blight). Leaves will quickly turn brown, but do not fall off the tree. The affected tree parts look like they have been burned in fire, thus the name.
Overwintering bacteria in the branches and cankers of infected trees multiply quickly once spring temperatures reach 65 degrees. Optimal conditions for the Fire blight bacteria include warm, wet spring weather during bloom time. The bacterial mass forces its way out of the pours of the stem, creating a bacterial ooze. Pollinators, aphids, flies and other insects inadvertently get this ooze on their bodies and carry it to the opening blossoms. Rain can also splash and spread the pathogen.
There is no cure for Fire blight, but the disease can be managed. The best preventative measure is planting disease resistant tree cultivars. There are varying degrees of resistance to Fire blight so do your research. Do not over fertilize in the spring as this will cause a flush of tender young growth that is most susceptible. Prune out all infected twigs and branches pruning 6-12” below the infected area. Sanitize your pruners with a 10% bleach solution after each cut. Dispose of the infected branches in the trash (no composting!). Fire blight also affects Bradford pear trees, and we are not sad about that.