I assume by fertilize that you are actually talking about polination correct? If so, and if they were slightly smaller than a baseball, chances are they were not actually polinated. Another possibility is damage to the vine (physical damage or possibly a vine borer), or perhaps cucumber beetles (they love to eat the tender shoots, flowers and fruit on pumpkin vines).

Thanks, all, for the advice. I sprayed the pumpkins again and stomped a whole bunch of squash bugs to death. (Does anyone know what the little tiny gnat-like bugs are that swarm squashed squash bugs the minute they are squashed?) I cut off all the bad vines and leaves and I'm inspecting the heck out of the onese that are left. So far, so good. If the bugs come back, I'll give up. I've had to baby these darn pumpkins so much already, I hate to give up without one last fight. The heat about killed them and kept them from setting fruit until just the last few weeks. I don't know, if my pumpkins will be ready for Halloween. This is my first year gardening and I think it will be my last year growing pumpkins! I'll let you know, if they make it...

If you want to be 100% sure it's not borer, you could take a knife and carefully slit the stem open to check. Either way, I would bury the damaged part of the stem so that it doesn't dry out and it will potentially form additional roots in that area. The danger of SVB and other damage to the stem is that water will be unable to be delivered from the roots to the end of the vine through the damaged stem. If you can encourage more roots to form further down the vine or near the site of the damage, water will have a clear path of delivery again. That is why many of the vine type squash are considered somewhat "resistent" to SVB, because they form roots at node sites, so even though a plant may be damaged by SVB, the plant doesn't die because the additional node roots keep the water flowing to the plant. Other squash are resistent because their vine is solid rather than hollow, and therefore a more difficult evironment for the SVB to settle into. Best of Luck! Susan

Could this be caused by heat or something non-contagious, or would you destroy these plants? Two of my mini pumpkin plants are growing (some not all) deformed flowers. The plants are side by side in an isolated spot but are different varieties, so it's not a seed thing. We have been having highs of 100-110 while these flowers formed, but then again none of my other pumpkin vines are doing this, including other plants of these same varieties grown in different spots in my yard.