I'm not going to claim to be an expert on this at all, but I've learned quite a lot recently. I've got a couple of clients with small orchards and I've been fighting fireblight for the last two years on one of them. I've been with my company for 2 seasons and I don't have prior records from this property so I don't know if they've had bad years previously. On my first season, it wasn't horrible, a couple of strikes here and there that I pruned out quickly. You've gotta prune them out because they will ooze bacteria that will spread by insects, rain, people, etc. This past season was worse, but from what I've heard from others I didn't have it incredibly bad. These are production/ornamental at a high end estate and looks are as important as yield. I've got a pretty good fruit tree program set up with about 8-10 treatments per season. It's one of those 'Oh sh*t!' problems because you feel like you're doing good, nice green full foliage one day, come back 3 days later and Oh sh*t! There are brown 6" curled over dead tips every where. The feeling of panic sets in and I wonder how bad this is going to be because you see more each day after you've pruned out what you can see.
Anyhow, my program starts with a hort oil at 2% with copper. Fungicides and insecticides through most of the remaining season. This past season, finished the season with a hort oil and copper treatment.
After the last two seasons, I didn't want another Oh sh*t! so I met with a consulting fruit specialist. He came out today and we discussed pruning, cultural issues and pest management. He suggested that I start with two hort oil and copper treatments. 4% oil on the first and 2% on the second. He also helped me put together different programs for apples, pears, and stone fruit that I'm still working on.
Additionally on fireblight, he suggested to follow a blight forecast model and if rainfall or any moist conditions such as heavy fog or dew is predicted, you've got to spray with streptomycin. The copper kills any bacteria on the trunk and limbs and it and the strep will help to significantly reduce blossom blight. This can be followed up with two applications of Apogee growth regulator as soon as the label allows (I believe it's green-tip). The copper sprays early and strep will help prevent the fireblight infections of the blossoms, while the growth regulator will reduce tip growth at the beginning of the season and somehow helps to prevent the twig blight that comes later and brings the Oh sh*ts!
Again, I'm not claiming to be an expert, I'm just passing on some info as it was presented to me (according to my memory, I don't have my notes). I feel like I know a good deal about trees, but I'm always amazed at how much more I don't know. I love reading KT's posts because it makes me do more research so I can truly understand half of what he's talking about. When I met with this fruit specialist today, I took tons of notes and it was like taking a whole class on fruit trees all in one afternoon. My head is still spinning with all of the new info and ways of looking at fruit trees and trees in general.
Another note in terms of pruning. You're not supposed to prune during the part of the season when you see the strikes, but you've gotta get rid of 'em or it'll spread. At this time I use lysol between cuts. It's a pain, but I don't want to take a chance. I also cut below the infection, but leave a stub if it's on a larger limb just in case I do spread it. Not sure if it makes a diff, but my convoluted theory is that if I accidentally spread it hopefully it won't spread beyond the stub. When I'm pruning in winter, I clean out the stubs and any fireblight cankers that I can find. I've read that you don't have to sterilize in winter since the bacteria are not active, but if pruning root suckers sterilize anyway.
Hope that all helped and doesn't conflict with anyone's non-chemical approach. If anyone's got a better remedy, I'm all ears. Oh yeah, and for ornamental apples or pears I'm pretty sure that you could use copper throughout the infection period if you don't want to use strep since you aren't concerned as much with the fruit. Copper won't damage the fruit, but it will cause it to russet, making it non-salable. A good, old-time chemical.
I also got help with brown rot on peaches and apricot, but that's another thread on another day I guess.