 It's called potato wart, and it's a highly destructive disease that can spread from infected potatoes and soil. It reduces crop yields, and there is currently no treatment available to eliminate it from contaminated farmland. The lawmakers said that currently the USDA does not require testing of fields on Prince Edward Island before the potatoes are cleared to be exported to the U.S. The top four potato-producing states in the U.S. are Idaho, Washington, Wisconsin, and Oregon.