Frequently we get requests for how to control Fire Blight.
Fire Blight in Apple Tree (Wiki Creative Commons - photo bySebastian Stabinger)
A) Fire Blight Resistance:
In Fire Blight prone areas, where possible, select varieties that are more resistant to Fire Blight. For example, the Pears in our catalog are shown with a Fire Blight resistant rating. There are varieties that never get Fire Blight in our observations and others that rarely show much effect. On the other hand, we are convinced that there are different strains of Fire Blight across the country so there is no guarantee that something we observe to be resistant might not get it somewhere else. As we learn about issues in other places, we adjust the ratings.
B) Environmental Cleanliness. See the links below for what University of California and Cornell University has to say. No need to duplicate it here.
C) Chemical Controls:
1) We cannot give you advice on chemical controls. That is the responsibility of your local PCA. And each state has different products registered for use in the state. In addition, home owners have far fewer choices than licensed applicators or nurseries have.
2) This is what we have been doing as of this writing for our production fields and budwood orchards in Visalia, California. Remember - this is not advice on what you can do - you must check with your local authorities and state regulations. This is what we, as a licensed and skilled nursery can do in our part of California with the products registered as of the time of this writing and not what a homeowner can do.
When we do get Fire Blight in a crop or two, our treatment regime is Agri-Mycin, a bactericide control agent, Allete, and then a copper spray, generally Kocide here. When it gets real hot, like around 95 or better, we stop the Kocide rotation as it can burn.
First thing to do is cut the plant back to green, uninfected wood, removing the infected wood from the area immediately. Burn if possible. Then apply the chemicals to the entire plant, especially the open wounds to help stop reinfection if the bacteria is still present. We spray in the rotation every 10-15 days until the threat of reinfection is over. Here, that means no rain for 3 weeks or better and normal humidity, which is low.
If it rains again, we auto start the rotation, on the sensitive plants (like Quince and some crabapples) without waiting for infection. If you wait to see it before you treat the young, sensitive trees, you won't have them be alive later. The mature trees, we would probably wait until seeing a strike unless you know the history of the plant in that area.
Hope this is helpful to get an idea, but do the due diligence for your location.
University of California Integrated Pest Management System page on Fire Blight
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7414.html
Cornell University Integrated Pest Management System page on Fire Blight
http://www.nysipm.cornell.edu/factsheets/treefruit/diseases/fb/fb.asp
6-28-2013