Thanks for writing. Unfortunately, there's nothing you can really do to repel whiteflies, but planting flowers, such as daisies, sunflowers, and marigolds near your pumpkins will attract beneficial insects that attack whiteflies for you. If you don't spray anything, the beneficial insects should keep the whitefly populations in balance.
Alternatively, there are several natural insecticides you can use. Most contain neem oil; look for them at your local garden center.
Good luck! I hope this helps.
---Justin, Senior Garden Editor, BHG.com"