Prices are driven by supply and demand — even at the grocery store. When there’s not enough of a product to meet our demand for it in the produce aisle, prices go up.

That’s what’s happening right now with lettuce in Arizona.

Yuma and Maricopa County grow approximately 90 percent of the winter lettuce crop for the U.S., but a voracious disease is threatening the crop — and driving up prices.

I spoke to Paul Brierley about this. He’s the executive director for the Yuma Center of Excellence for Desert Agriculture, and he’s been working with growers on field trials to fight what’s called Fusarium wilt, a disease that impacts the soil and, right now, has no cure.