Well, it sort of depends somewhat on other factors, like the spacing of the corn, the type of weeds, and especially on the soil moisture status. Short weeds like clover or purslane and rich, moist soil won't really cause a problem. Tall, rampant weeds that are competing for limited soil moisture in a drought situation with corn that is already stressed can definitely cause a problem and diminish both quality and quantity of yield.

Personally, I use great big sheets of black plastic, and it does a super job of keeping down weeds and keeping in the soil moisture. I use a power drill with about an 1/8th inch drill bit to go right through the entire roll in many spots before I unroll it onto the beds, so the rain goes right through. These holes are too small for weeds to pop up through 99.999999% of the time (once in a blue moon a weed grows through one of these holes). So, the only real weeding is a weed or two through the larger planting holes, which I burn out with a propane torch, a circle about 3 to 4 inches across. But, weed it once or twice, which takes like 5-10 minutes for a great big patch of corn (say 20 x 100 feet) and it's done for the whole year.

You could use other approaches, too, mulch, etc. If you have good reliable rains or a watering system, you could even turn this whole thing around and actually plant white clover, birdsfoot trefoil, or some other low growing cover crop between the corn to make a living mulch.

I would say that, if the corn looks the least bit stressed, such as it isn't growing as fast as you think it should be, I would do what I could to get some of the weeds out of there. You wouldn't even necessarily have to pull or kill them, just cut them way back so that they are taking up a lot less of the soil moisture and fertility (would mowing between rows be an option at all?)

Thanks for the help.

i plant my corn so i can cultivate it with my tiller with the plow on. this keeps the weeds down and puts air into the soil around the corn. the corn does much better with this treatment.

WM