Recently I've had a number of emails from growers talking about cracks forming on the stem of their pumpkin. 95% of the time, at this point of the season, it is because of roots on the main vine just before, just after or directly under the stem or on side vines right next to the pumpkin that are holding the stem down as the pumpkin grows up. At each leaf node a root will form out of the bottom of the vine and out of the top of the vine. You need to remove those roots and any dirt covering the top of the vines so that as the pumpkin grows the vine can lift up with the pumpkin. Otherwise those roots will hold the vine down and something has to give and usually it is going to be the stem of the pumpkin. I pull all of those roots up early on and then check to make sure the vine has a little slack in it as the season goes on. You can crack the stem and vines if you don't watch it closely. I've had it a couple of times (this year as a matter-o-fact) where I pulled the roots up and a week or two later they had reattached to the ground so you have to watch them closely.
This evening I sprayed some foliar multi-mineral on both plants.