Before the real pro's get here, I'll start the request for additional information. What zone are you in and where are you located? From what I've learned here, you either want to prune in summer (to limit growth) or late winter/early spring (to shape growth) - depending on what you are trying to accomplish.

Second, are there any signs on the tree, particularly these two major branches that are dead, that would give any clues as to why they are dead? What were the condition of the leaves this year and last, any sap oozing out of them, any insect damage, wind break them off? Lastly, if you could post a picture or two, a close up of any signs of damage, as well as an overall view of the entire tree, that could give additional perspective.

With this additional information, the people here will be in a better position to help you and your tree.

James:

I certainly agree with cyclewest's request for more detailed information, but if two out of three major branches of the tree are dead, the remaining branch cannot be far behind. Your tree is probably being killed by bacterial canker or a similar peach tree disease. I would figure on taking that tree out and planting a new one in a different location. If you do plant another one, don't wait 8 years before learning what it needs in the way of care. In most locations, peach trees need dormant spraying with copper to suppress the development of disease that shows up during the growing season. Without some level of care, particularly spray care, the life of a peach tree can be very short.

Don Yellman, Great Falls, VA

Thanks for the replies. For Cyclewest's question. We live in Milpitas, California (San Francisco Bay Area). We did our last trimming mainly for the tree shaping and expected a better growth of the tree. I call the branches dead is because nothing comes out of the branches (no leaves at all) since the Spring while the other one is full of life and is still producing peaches. Jellyman suggested that bacteria or a tree desease might be the cause. If that is the case, should we cut off the dead brances and what kind of spray care we need to do? I will post some of pictures in a couple of days. The bottom line is I really like to save the tree.

Here in SoCal, my fruit trees survive and maintain even with persistant canker (ie. brown, jellylike oozing). My peach tree did well, the nectarine has been fine for many years. The cherry didn't make it long, but was probably do to insufficient chilling hours (canker seems to be very common here in SoCal). The trick is to do your copper-sulfur spraying in winter and then cutting out the bad areas in the bark (and disinfect the area and tool). The trees will never be completely free of canker, though, regardless of the effort to "cure" it.

Also, look on the "dead" limbs for holes, ie. borer insect damage. If so, ask your nurseryman what to use (I used horticultural oil, but I don't remember the name).

If one limb is healthy, you may be able to save the tree. There's still time this season to give the tree a boost of fertilizer, nitrogen (but don't overwater... and don't underwater a "sick" tree). Good luck!!! Pics will help for others to give further advice.

Oops sorry, I use lime-sulfur for winter, dormant spraying.