Story, first published: Astounding Science Fiction, Oct. 1938
A strange plague that starves people to death is part of a plot by Martian scientists to regain control of the Solar System. Only New Chicago on Venus, a colony of transplanted farmers from Iowa, seems relatively immune from the disease. A newspaper reporter and an alcoholic doctor stumble on the antidote, the polka-dot weed, and announce the news to the Solar System. The depressed Iowa farmers, who had been gulled into coming to Venus by an unscrupulous land company, are now rich beyond their wildest dreams. Despite a raid by a Martian spaceship, thwarted by the old town marshal at the expense of his life and the machinations of the land company, Iowa horse sense and frontier justice prevail to save New Chicago and the Solar System.
Ewald, Robert J.: When the Fires Burn High and the Wind is from the North, p.27