Ask a Gardener – Fire Blight

Thursday March 3, 2016

I have fire blight on my crab apple tree. It seems to have gotten significantly worse just in one day. Is there any product that will treat this systemically, as I cannot reach the top to cut out the affected branches? Also, if I cut the branches now, will the disease spread because there are open wounds, even if I sterilize the pruners in between cuts? I think this might have been brought on by a squirrel that decided to chew up some branches for a nest, and thus left open wounds for the disease to enter the tree. We noticed the disease last summer after the extensive hail and rain, and did not notice it this spring, until the past weeks of almost continuous rain. Any help would be appreciated. Thank you. – Ann


Oh, no! Well, if it’s any consolation, you’re not alone. A lot of people have reported fire blight this season. Our wet spring created the perfect conditions for the spread of this bacterial disease. Sadly, fire blight cannot be cured, but there are some things you can do to control and manage it.

Fire blight isn’t spread through damaged tissue; it’s spread through the tree’s blossoms. So your culprit was more likely a bee than a squirrel. But he didn’t mean to! Fire blight bacteria lays dormant over winter and then emerges in the spring as a lovely substance appetizingly called “bacterial ooze.” While making their pollination rounds, bees and other pollinators unintentionally pick up the bacteria and transfer it to the tree’s flowers. Once in the blossoms, the blight multiplies quickly in the nectar and spreads into the branch, where it will eventually kill it.

Right now, about the only thing to do is prune away the diseased parts of the tree. Just like you said, it’s extremely important that you sterilize your pruners between each and every cut. Dip them in bleach, rubbing alcohol or another disinfectant between cuts. Prune the twigs or branches about 1 foot below the infected area and be sure to destroy all the cuttings. This fall, carefully rake up the leaves dropped by the tree and destroy them as well. This should help prevent the spread of the disease.

Unfortunately, there is no systemic product that will control fire blight. About the only thing available to home gardeners for fire blight control is a foliar spray by Fertilome called Fire Blight Spray. Fire Blight Spray is an antibiotic called streptomycin that can be used to control fire blight on fruit trees, flowers and shrubs. Fire Blight spray should be applied just as the tree is starting to bloom in the spring, before you notice any symptoms. You’ll need to apply a few times throughout the blooming period to make sure you hit all the blossoms. As always, be sure to read all the directions before using.