Pumpkins get grapefruit to cantelope size then shrivel up

This is my first attempt at growing pumpkins, The vines are 50feet long with lots of female flowers that turn into small pumpkins, but after a few weeks or longer the fruit shrivels up. Now I have 1 cantelope sized that has started to shrivel, another is almost watermelon sized, I don't want to lose it as well. I water moderatly, haven't fed them.The temp range here is 68 at night, 80 during the day. The vine is healthy, lots of leaves and flowers. This has started almost from day one about 15 pumpkins ago. Please help!

 

Here is a link to a Ohio State University website which describes the reason that pumpkin fruits abort.

Raakel

 

Notwithstanding the explanations given in the linked OSU article I would recommend that you try hand pollinating. Gather three male flowers for each female. Tear the petals off the males to allow easy manipulation. Apply the stamin from the male flower directly to the corresponding part of the female, rubbing all its exposed surface, then repeat with each of the other two males upon the same female. The stamins can be left inside the female flower once you have completed the exercise.

I find that most years insects are not reliable pollinators or at least not quick enough for me, at least early in the season, as I am trying to grow giant pumpkins for which each day of delay in pollination is about 30 pounds lost in final weight.

RL