How can I prevent fire blight from infecting new apple trees when old trees in the area have been affected?
Question:
I have an old farm with 200-year-old apple trees and some have been infected with fire blight. I am planting some new apple trees and want to know how to plant them so the fire blight doesn’t infect the new ones. Is there a distance recommendation or specifics about how the disease is spread so she can protect the new trees?
Answer:
I’m sorry to hear about the fire blight woes!
First, if you are at all in doubt, I recommend submitting photos or a physical sample to the UMaine Plant Disease Diagnostic Lab. There is a small charge for their service, but you will receive definitive confirmation of the diagnosis and specific recommendations.
Fire blight (Erwinia amylovora) is a bacterium-based disease that affects many member of the Rose family, apples obviously included. It is highly contagious and transmitted by wind and rain; data surrounding transmission by contaminated pruning tools is varied (standard advice is to sterilize between specimens, but some studies have shown this doesn’t impact fire blight as much as expected), but I would still recommend practicing good sanitation hygiene. Because of the methods of transmission, I’m not aware of any specific advice about planting distance being a helpful mitigating technique.
The first, best line of defense is to plant a resistant cultivar, though you should know that even those can be infected during heavy years–no apples are completely immune. The next lines of defense are proper pruning out of the infected parts and chemical intervention (both discussed in the following links).
Colorado State University Extension fact sheet on Fire Blight
Washington State University Extension study on Fire blight susceptibility of apple cultivars (including results for numerous common apple types)
Cornell Univ Extension list of susceptible and resistant cultivars
Good luck, and happy gardening.