Evaluation of Management Tools for Fusarium Wilt of Lettuce in 2004

Abstract

Fusarium wilt of lettuce was first recognized in Arizona in 2001. Since this first discovery, the pathogen, Fusarium oxysporum f.sp. lactucae (Fol), has been recovered from infected lettuce plants from approximately 30 different fields. This fungus is a soil-borne pathogen that can remain viable in soil for many years. Cultural disease control measures, such as extended soil flooding and soil solarization, have shown promise in managing Fusarium wilt in other cropping systems. The specific objectives of this research were to repeat preliminary soil solarization and flooding experiments conducted last year and to evaluate the effect of preplant treatment of planting beds with either Vapam or soil solarization on the subsequent incidence of Fusarium wilt on lettuce. In a microplot study, soil naturally infested with Fol was flooded or solarized for 15, 30, 45 and 60 days, then bioassayed by transplanting and growing lettuce plants in samples of treated soil as well as nontreated soil. In field studies, plots were solarized for 40 days or treated with Vapam before planting to lettuce. In the microplot experiment, the severity of Fusarium wilt on lettuce grown in previously flooded or solarized soil was significantly less than that in nontreated soil. Additionally, there was no difference between flooding and solarization with respect to disease severity, as lettuce plants in both cases had virtually no symptoms of Fusarium wilt. Weight of the tops of lettuce plants was significantly greater for plants grown in flooded or solarized soil compared to that in nontreated soil. Furthermore, top growth in solarized soil was sometimes significantly greater than that in flooded soil. Compared to nontreated soil, root growth in solarized soil was significantly greater. In contrast, root growth in flooded soil was not significantly different than that recorded in nontreated soil. In the field studies, the incidence of lettuce plants with foliar symptoms of Fusarium wilt was reduced by an average of 42% when grown on solarized beds compared to nonsolarized beds. Preplant application of Vapam at rates of 30, 45 and 60 gallons of product per acre resulted in reductions in the incidence of Fusarium wilt of 38, 50, and 45%, respectively. Further work is needed to attempt to increase the reduction of disease recorded this past year. Refinements in our solarization technique as well as application methods for Vapam may increase the efficacy of these tools in reducing the incidence and severity of Fusarium wilt of lettuce.