For the passed two years my summer squash and zucchini came up grew well and...
For the passed two years my summer squash and zucchini came up grew well and developed many blossoms and started to form and then they turned brown, then black and died. Why does this happen and what can it do to stop it. I also have problems with my tomatoes plants turning brown. My worse problem is deer in city that eat all my plants.
There are two reasons why your squash flowers are falling off.
1) Your plant only has male flowers and so the flowers will wither, discolor and fall off. .Other plants will have only female flowers and some have a mix of both types.
2) Pollination is not occurring between the male and female flowers. You can identify the female flowers by having a small fruit below the female flower. If the female flower is pollinated by pollen from the male flower, then this fruit structure will grow and develop into a full sized fruit. Without pollination, the female flower and associated fruit do not develop and thus wither and die.
Early in the spring, honeybees and other pollinators are inactive due to cool, cloudy wet weather and so there are problems in fruit development. You will also need to be aware if one of your neighbors has sprayed pollinators then they may wipe out the pollinators you need for fruit to develop.
Pollination can be done by yourself using a small brush or Q-tip swab to transfer pollen from the male flowers to the female flowers. The male flowers are open and viable for several days. The female flowers are only open and viable for one day, so you will have to pollinate daily to ensure fruit development.
You mention your tomato plants turning brown, but give no details, so it is difficult to know how to help you, but for general information on tomato diseases and pests. Check out http://vegetablemdonline.ppath.cornell.edu/DiagnosticKeys/TomWlt/TomWiltKey.html
Deer are a continual problem and I wish I could offer you more support, but right now using fencing and other deterrant methods. Check out http://www.wvu.edu/~agexten/wildlife/deercont.PDF for more assistance.