My problem here is rain during the first part of the season. Once July hits we are super dry. And the transition is part of the problem. The plants are use to heavy moisture, then it becomes dry. I rarely water until July. I also leave off mulch on new plantings till July, when it does help retain moisture.
Not all mulch is equal. I use pine bark and pine straw. Both break down very slowly, so it is useful to retain moisture, and to keep weeds down, but not really a source of nutrition. They just breakdown too slow to be very beneficial. I have bark pieces over 3 years old, and have yet to breakdown,

Hman,

Thanks for posting. After reading your post, initially I was under the impression the research had been partly conducted with fruit trees. I looked for the blog online and found the the full article. I see now you were applying their research on ornamentals, to fruit.

Mulch does preserve more ground moisture. As we've discussed here before, I think it's the shading (and weed control) which increase soil moisture, as well as perhaps the breakdown of the mulch, which you've pointed out.

I wouldn't necessarily dispute your theory that mulch has the potential to decrease fruit quality in rainier climates. You mentioned you've observed this in your own orchard. I've noticed after very heavy rains (i.e. 2" rains or days and days of consistent 1/2" rains) the peach quality goes down. But I've noticed the same thing from unmulched fruits like strawberries. Incidentally, that's why I will never grow strawberries commercially. They ripen during the rainy season here and don't taste any better than store bought. (We have a small strawberry patch, but just for home use.)

I've noticed the "rain effect" on peach quality is short lived. In other words. It only affects the peaches for about 5-7 days after the rain quits. This is perhaps because the hot days quickly start the peach trees to pull a lot of the excess moisture out of the ground. I'll note that I don't mulch quite to the drip line on mature peach trees (although I do on young trees). This would also have implications on the availability of water to the trees, as many of the feeder roots would extend out past the drip line into the sod, where the ground would naturally dry out faster.

I've noticed the excessive rain affects the most shaded peaches the most. The ones on top of the canopy aren't nearly as affected.

I still maintain some varieties are more affected by rain than others. It's a possible explanation why you don't like Redhaven quality in the East, whereas Redhaven is generally a top quality peach here. Redhaven ripens here, in mid to late July when temps are blazing hot, the sun is high, and the ground is generally bone dry (Another possible explanation is that I read a few months ago that there are numerous "strains" of Redhaven floating around. I wasn't aware of this before. One person's Redhaven may be different than anothers.)

Olpea, the point I was making is that if the mulch increases the growth of establishing trees this much, it is more evidence that it increases the vegetative vigor with established trees the same way- not that anyone disputes this, but the research here (just a single site over 2 seasons, so not really all that definitive) gives an idea of how stimulating it can be and indicates that it is mostly about water retention.

It has been established that deficit irrigation can increase brix content of many types of fruit, so excess water would likely (or surely does) reduce brix

I would expect this all to affect fruit trees in widely different ways even from cultivar to cultivar, as you suggest- but also in your stronger sun it might matter less.

When you talk about rain during ripening, it is not necessarily excess water that is the primary or only problem, I expect it is the blockage of the sun's rays as well.