• Kelly Grummons

Q: My crabapple and my mountain ash tree got fire blight – should I prune affected branches?

Q: My crabapple and my mountain ash tree got fireblight this spring worse than usual. The crabapple tree is about 40 years old and the mountain ash is 7 years old. Someone told me that I have to prune out all of the affected branches. Is this true?

Fireblight Photo: Wikimedia Commons
Fireblight Photo: Wikimedia Commons

A: Erwinia amylovora is a bacterium known as Fire Blight and is a serious disease of plants in the rose/apple family. Most of my customers are primarily concerned about its effect on their apples, pears, mountain ash and crabapples. Conventional “treatment” was to prune out affected branches. Also, the antibiotic Streptomycin was applied to flowering plants to protect them from the bacterium.


Fire Blight is mostly inoculated into the plant via the stigmas in the flowers. The disease is vectored via pollenating insects from diseased plants to non-diseased plants. The stigma provides direct access to the plant’s vascular system.


The great news is that now we can PREVENT the disease to a great degree by spraying plants in flower bud and bloom with protective “probiotics” such as other beneficial bacteria, Streptomyces lydicus and Bacillus subtilisw. These can be found in various over-the-counter disease prevention products or online. They are safe to use and can be used for organic culture.


In the meantime, it may be best to prune out the dead branch tips cutting several inches back into the green “healthy” wood. Sterilize your pruners before every cut with a solution of 10% bleach in water. Next year, be prepared to spray the probiotics in April.