Lay cardboard over the area, weigh it down with a thin layer of soil or rocks and cut holes for planting.

Your suspicion is correct -- nothing brings up the weeds and, worse, rejuvenates the grass, better than tilling up land that's been lying fallow.

I second cardboard. I've used newspaper too -- in areas that don't get a lot of wind and which have abundant rocks.

A heavy mulch of last fall's leaves is good too.

You can lay the summer's grass clippings on top of the cardboard in thin layers and then top that with this coming fall's leaves after harvest for a combination of ongoing weed smothering and soil improvement.

Just a note though about something that may not be applicable in your zone - since you presumably want your pumpkins in October rather than August, it may be possible to calculate back from your desired harvest and till several times at 2-3 weeks intervals before the planting date so that weeds sprout then get killed. This reduces the weed seed population.

Or you can do it like we old folks. Culivate. leaning on a hoe is very therapeutic.

I was thinking of an early spring tilling then planting buckwheat.

Knocking down the mounds to plant the pumpkins.

Then finally knocking down all of it when the vines take off.

Looks like I need to plant these early.

So maybe I mound up a hill/row.
Cover crop on both sides.
As they both grow, and the pumpkins start to vine I mow the cover down?

I live in Australia and im growing pumpkins (queensland blue). I have a large piece of old carpet with a hole cut out of the centre which the pumpkins are growing out of. I dont have any problem with weeds or it blowing away but I do have rocks on the corners to hold it down.

I am also growing squash and I am just using straw as a weed preventive. Once the straw has been wet it doesent seem to blow away.

I would recommend against a cover crop next to the pumpkins. Too much competition for nutrients. Cardboard and organic carpet both sound like good ideas. I have been using wood chips, but cardboard might be cheaper.