An agricultural official says prices for winter lettuce grown in southwestern Arizona are rising because of damage caused by freezing weather.

The Yuma area provides much of the nation's leafy greens during the winter, and farmers are reporting damage to many romaine and iceberg lettuce crops.

Kurt Nolte, a Yuma-based agricultural agent for the University of Arizona, says the current cold is freezing the heads of the lettuce and affecting the quality and yield.

Nolte says the price for a carton of lettuce in Yuma two weeks ago was $7 to $8. As of Monday, Nolte says it was $20 per carton.

He says it's virtually impossible for farmers to protect their lettuce crops with 80,000 acres to cover in Yuma County.