Sorry to hear that. I don't think I have an answer for you, but I had a nectarine tree die this summer as well. It did exactly the same thing. it looked great in the fall and spring, then turned brown in the summer, then it sorta greened up a little, but then the heat fried it again. This time I think it's just dead for good. I guess I will have to cut through some branches to see if there's any green there, but it doesn't look good. One mistake I made was to plant it on sort of a hill. I have a part of the yard that is raised up, so in the future I think I will make a depression/basin where the water can gather and soak down. Also, I noticed that the PH of the water this summer was really high, then I made another mistake to use the pool water to water my backyard without adjusting the PH (I didn't bother to balance the PH, it's a small pool the kids) When I measured the PH the next time I had to dump the water out, it was like 8.4 or maybe more, and I can tell that the trees hated it. After that I got smart, I lowered the PH and left the water to sit for a couple of days for the chlorine to evaporate before dumping it on the trees, I think that helped. I also started to use some gypsum and sulphur. I spread it around the trees. Most of my trees struggled this summer, even my fig tree. I think the long dry season didn't help. I'm in Peoria BTW.