Hi Rob,
I'm no expert, but are the flowers even CLOSE to being ready to open? If so, you could cut them open & hand pollinate. I've done that 2x so far this year because my male flowers die before the females open, and it worked! It's a thought.... who knows! I have no idea what could cause this for multiple seasons. Standing water is always an issue, but since pumpkin roots are shallow, most soils will drain well enough. If not, mix in some sand.
Good luck! -Katie

I agree. It sounds like a lack of pollination. We had the same exact problem last year. I saw no bees in the garden and most of our little pumpkins shriveled and died.

The bees came back this year and it's a different story.

If you don't have a lot of bees around, you might as well try hand-pollinating your pumpkins.

Here is a great description of how to pollinate by hand : http://forums.gardenweb.com/forums/load/gourds/msg0611545713356.html

Here is a link that might be useful: Smith Family Garden Blog

Hello all,

Our pumpkins are doing the same thing. Some of the fallen ones were smaller than a marble, and none of the flowers opened. Only one was close to opening, and was probably 3-4 days away when it fell. The baby pumpkins turn yellow, the unopened blooms turn brown and they eventually fall off. We have no lack of male flowers or new baby pumpkins, but no female blooms :(

We've fertilized, water adequately...it's been really hot the past week, could that be the problem? There is no evidence of pests or rot or anything else. The plants themselves are really healthy.

Any help appreciated...

- Star