Unfortunately there is no easy answer.    Many of the pesticides required for pumpkin production are restricted-use pesticides and require a pesticide license to purchase.  Preventing weed establishment is the most effective means of control. Black plastic mulch or a 2-4-inch layer of organic material will keep weed seeds from germinating.

After weeds have sprouted, regain control by pulling, tilling or hoeing. A scuffle, or action hoe, works well where mulch is thin before the pumpkins begin to vine. This tool has a flat blade on the bottom of a handle-shaped loop of metal. It provides a relatively easy way of slicing off the tops of plants, which eventually starves the roots.

 Here is a link to pumpkin production facts developed by Penn State Extension.   http://extension.psu.edu/business/ag-alternatives/horticulture/melons-and-pumpkins/pumpkin-production  

Here is a link to a more extensive discussion of weed control in pumpkin patches developed by the University of Illinois extension service.   Page 6 of this publication lists all of the herbicides used for pre emerge and post emerge control and the specific weeds that are targeted.
http://ipm.illinois.edu/ifvn/presentations/pumpkins/wahle_weed.pdf  

Good luck with your efforts.