I bought and planted a peach tree three weeks ago. at the beginning it had a beautiful flowers and later peaches. recently, we had too much rain in Houston Texas. after the rain the leaves are almost dying.
is that because of too much rain or less rain and fertilizer?

A picture of the tree, close up of the leaves, plus one of the whole area including the tree would help a lot.

Did the tree stay wet for days and days during the heavy rains and flooding? If it's in a low spot, or the soil settled in that area from the wet weather, it could have been wet for a while even after the flood water was gone.

It could have some root rot going on. The roots basically drown without some air in the soil i.e. drying out between heavy waterings.

Hm, the leaves are really going reddish, rather than brown. You didn't have a sudden cold snap recently, did you?

I'd try a douse with some dissolved Epsom Salts - about a tablespoon dissolved in a gallon of water. It is basically magnesium sulphate, and magnesium deficiency can look like that, a reddish color to the leaves. If it doesn't respond, by greening up again, then another solution might be the ticket, but the Epsom salts surely won't hurt. If it does work, you'll see a difference in color in a few days, and you should put another gallon on after a week or so.

Have you given the tree any fertilizer since planting it? A balanced, timed release pelleted fertilizer for fruit trees would be a good idea about now if not.

I hate to say so but that little tree is really much too young to support producing fruit. The first year after you plant a fruit tree, you really should remove all the fruit to let the tree grow a good root system and lots more leaves. Nobody likes to hear this advice, I know.

In case it helps, the symptoms of specific nutrient deficiencies in peach are pictured here:

http://www.clemson.edu/extensi...

Wow, feeding peaches is complicated! Great site.