A few cases of fire blight on ornamental pear have continued to appear at the Plant Clinic this past week. We discussed this topic in issue no. 2 of the newsletter. In that article, I mentioned that resistance to this bacterium is available in ornamental pear. I also said that if you are thinking of planting new trees, you might do a bit of searching for resistant varieties. I listed ornamental Callery pears ‘Aristocrat’ and ‘Autumn Blaze’ as having good resistance reports. In two separate cases this spring, the Plant Clinic confirmed fire blight on ‘Autumn Blaze’ Callery pear. In fact, a Kansas publication that you can find on the Web at http://www.utextension.utk.edu/publications/spfiles/SP277-R.pdf lists Autumn Blaze as very susceptible to fire blight.
This brings up the issue of fire blight resistance information for Callery pear. It can be confusing and conflicting, depending on the list consulted. I don’t have an answer to the problem nor a list that is any better than anyone else’s. Part of the problem is inadequate testing due to limited time and money. Cultivars should be tested at multiple locations representing a wide geographic area, multiple times, and under various disease pressures. Obviously, this does not always occur. Possibly the bacterium has changed. The fact is that some Callery pears “resistant” to fire blight may become infected. Possibly sticking to cultivars that have been proven winners in your area is the safe route.