Carolyn, I've read in several places that the disease can be killed in very cold northern winters, though I'm not sure how reliable that is. This says 5° is the magic number, but I question "for how long?"
"They are reliably killed when winter temperatures drop to below 5 degrees F. This seems to be a contributing factor in the rise of this plant pathogen here on island. We haven’t had severe cold here in a few years. "
That's from here
http://www.nantucketchronicle....
Karen
