Question
I live in Western PA and my zucchini have been planted in my garden for about a month now.  We have had a good bit of rain since I planted them and they get sun just about all day long.  The first 3 weeks they looked healthy and were growing as expected.  Then all of a sudden one of them that was already flowering and then producing small zucchini was wilted and basically looked deflated like someone left the air out of it all in one day.  I watered it and the next morning it looked good again.  But as the day progressed it starting wilting again and this time I tried watering, miracle grow and that dust for mites and bugs with no luck.  I did not see any bugs or larvae but it looks like this plant cannot be saved.  Then the next day the plant right next to it started wilting and has the same symptoms.  I only have 3 more plants left and am expecting they will end up with the same fate.  My soil was shocked and manured prior to planting along with mulch after the plants were put in the ground along with those weed rolls you lay on the ground and punch holes to put the plants through.  That also keeps the ground very moist under it.  So the ground is mineral rich.  I don not know what they have or what I can do to save the remaining plants.  I may be afraid to plant them next year.  Please help.

Answer
It sounds like you have the squash borer - look at the stems of the ones that are wilting (cut open the one that is most wilted) and see if you see tunneling, some sawdust like material (that's the larvae poop) or the larvae itself.  The adult is a moth that looks like a wasp, and it lays eggs under the stems of the plants, the larvae tunnels into the stems and they collapse.

There are a zillion ways to deal with squash borers - if you google them you'll find more then the following:
1. dig out the larvae and bury the stem beyond it - keep the area moist and the stem often re-roots.
2. Put on a garden glove and pour some rotenone dust (or rotenone pyrethrin dust) into the glove and rub it under the vine.
3. Keep the squash under floating row cover most of the time - you'll have to uncover every morning for a couple of hours for the bees to pollinate, or you can hand-pollinate with a paint brush.
4. Some people find success with putting sheets of foil under the vines to confuse the moths, and squirting shaving cream over the vines to prevent them from laying eggs on the stems.

Be sure to cut out the larvae and distroy.

I hope this helps!
C.L.