The hot, dry weather across most of the Midwest could be a blessing in disguise for Iowa farmers. When it looks like the grain crop will be poor, prices begin to go up in commodity “futures” markets, and Iowa State University Ag economist Bob Wisner says there’s already a supply-demand gap of the kind that drives up gas prices.Even with normal yields of an average 140 bushels an acre nationally, we used more corn than we grew last year, and seem to be heading that direction again this year, so markets are nervous. At this point, Iowa could have the lead in the harvest outlook. Even before this week’s drenching rain, Wisner says two-thirds of Iowa’s corn crop was rated in “good to excellent” condition.That would mean normal yields or better, but in Nebraska the good-looking crop’s only 45-percent of their corn, and it’s just 42-percent in South Dakota, 48-percent in Indiana, and 53-percent in Illinois. If bad yields elsewhere drive up prices, Iowa farmers could cash in, though a windfall’s not yet guaranteed. The crop could still recover, but more drought and heat could do more damage. By the same token, last week’s rains could revive grain in parched areas, pushing crop estimates up…and prices back down.