According to the Missouri Botanical Garden, end rot disease is one of the most common reasons why pumpkins fall off the vine before ripening. Pests, improper watering techniques, mold and mildew can also affect pumpkin growth.
Blossom end rot is typically caused by a lack of calcium. The Missouri Botanical Garden recommends using a spray that contains a 1 percent solution of calcium chloride to treat blossom end rot.
According to North Dakota State University, cucumber beetles can also cause small pumpkins to fall off the vine. The beetle can be eliminated by using a commercial or organic pesticide.
Pumpkin rot can occur when the ground is too wet. Bonnie Plants recommends watering pumpkins early in the morning to ensure that leaves and vines dry quickly. Plants that are wet for too long are susceptible to rot, mold and mildew.