Pumpkin plants have no pumpkins this year?
Allegheny County Pennsylvania
Pumpkin fruit set may be affected by a number of factors. Excessive plant growth due to improper application of higher than recommended nitrogen applications can delay flowering and fruit set. Too much moisture in the soil can damage the pumpkin plants' roots, debilitate the plants, and cause flower and fruit abortion. Flower bud abortion may also occur if temperatures are in the high 70's at night or in the high 90's during the day for several consecutive days. A major factor that can diminish fruit production is poor pollination when flowers abort or fruits are malformed due to insufficient pollinator activity. The three main pollinators of pumpkins are honeybees, bumblebees, and squash bees.
Successful pollination requires the pumpkin grower understand the biology of the various pollinators and provide a suitable environment. Pesticide use must be carefully managed to avoid bee kills.
Here is an excellent article about pumpkin pollinators and pumpkin fruit production: