Wilting Disease Threatens Arizona's Lettuce Crop

Growers in Arizona and around the world are concerned with the spread of a wilting disease present in soil that can damage lettuce.

In response, researchers and lettuce farmers are gathering in Yuma this fall to brainstorm ways to protect one of the region’s important crops.

Lettuce wilt looks as you might imagine — the fungus makes plants look dry and brown. The disease can kill the plant, too, if infected early — causing whole fields to be destroyed.

Plant breeders are creating types of lettuce resistant to wilt, and researchers are also evaluating how effective a range of other tools — including crop rotation, field flooding and delayed planting — might be in combating the disease. But no silver bullet exists.

“Right now, the only solution is to not grow lettuce in the particular field that’s infested with it, and eventually, you run out of fields to grow lettuce in," said Paul Brierley, director of the Yuma Center of Excellence for Desert Agriculture.

His newly formed organization is funded by the agricultural industry and housed within the University of Arizona.

Through polling growers, Brierley identified lettuce wilt as a problem in urgent need of more research. The disease was first seen in Japan in the 1950s, and is now present in California and Arizona fields, as well as agricultural land in Argentina, Brazil, Italy and Iran, among others.

“We’re hopeful that bringing all this brainpower and experience together in Yuma will solve problems that affect the entire world, because this is something that affects all these other countries, also," Brierley said.

In Arizona alone, lettuce is a more than $350 million industry, according to the USDA.

The Yuma Center of Excellence for Desert Agriculture will host the conference in November, with funding from the USDA.

In addition to researchers sharing knowledge with growers and getting feedback from the field, the participants will pinpoint a short list of projects that are most likely to yield tools to combat the disease

(Photo courtesy of Michael Matheron - University of Arizona)

The fusarium fungus enters the plant through the roots, causing lettuce to wilt or die.

(Photo courtesy of Paul Brierley - University of Arizona)

This leaf tissue is infected with Fusarium oxysporum f. sp. lactucum, the fungus that causes lettuce wilt, as seen through an electron microscope.