Evaluation of Soil Solarization and Flooding As Management Tools for Fusarium Wilt of Lettuce.

Fusarium wilt of lettuce caused by Fusarium oxysporum f. sp. lactucae continues to spread and cause economic losses in Arizona lettuce fields since the initial discovery of the disease in the state in 2001. Studies were initiated to assess the potential of summer soil solarization and flooding as management tools for Fusarium wilt of lettuce in southwestern Arizona production fields. In microplot studies, lettuce plant growth in soil naturally infested with F. oxysporum f. sp. lactucae that was solarized from 2 to 8 weeks was consistently greater than growth in nonsolarized soil. Growth of lettuce in flooded soil containing the pathogen occasionally was significantly higher than in nonflooded soil; however, the effect on plant growth and health was not as consistent as that recorded for solarized soil. In four trials within a field containing F. oxysporum f. sp. lactucae, the incidence of Fusarium wilt on lettuce sown in soil after solarization was reduced from 42 to 91% compared with disease in nonsolarized plots. There was no significant benefit of a 2- over a 1-month solarization period under the conditions of these trials, where the mean soil temperature at a depth of 5 cm during a 1-month solarization period in 2005 and 2006 was 47 and 49°C, respectively. These findings suggest that soil solarization can be an effective tool for management of Fusarium wilt on lettuce, especially when used within an integrated program in conjunction with existing disease management tactics.