2000 - 2001 Efficacy Evaluation of Selected Fungicides
Against Spinach White Rust DiseaseBy Frank J. Dainello, Larry Stein, Marcel Valdez, and Kenneth White
hite rust is a major problem for Texas spinach growers. As a result, the Wintergarden Spinach Producers’ Board has been funding on-going programs to develop effective strategies for managing this disease. Based on previous research, fungicides were found to be a key component in a sound management strategy. Therefore, the Texas Agricultural Extension Service has been screening fungicides for efficacy against spinach white rust since 1996.
The primary goal of our efforts has been to find an effective fungicide that can be applied as a foliar treatment to supplement the efficacy obtained from Ridomil Gold in-seed furrow treatment. This report describes the findings of our most recent effort.
The 2000 - 2001 evaluations were conducted in conjunction with the Del Monte Foods research group at their Crystal City research farm. Twenty-four treatments (shown in Table 1) were evaluated in a randomized block design having four replicates per treatment. Each treatment replicate consisted of a 4-bed plot 40 feet in length. The center two beds served as the treated area, and the outer two beds as treatment buffers. Two seed lines of the white-rust susceptible variety ‘Cascade’ were sown per bed on October 25, 2000. The Ridomil Gold soil treatments were applied at planting.
Initially, the spray schedules were to be started at the 4-true-leaf stage, and applied on a 10- to 12-day schedule. However, unfavorable weather conditions created a need to revise this plan. The initial foliar application was applied on December 7, and then repeated on December 19, January 4, 31, and February 14. The treatments were indexed for efficacy on February 26. Results obtained are presented in Table 1.
The data presented in Table 1 indicates that all but five treatments significantly reduced the incidence of white rust infection as compared to the untreated check. The white rust incidence is reported as percent-leaves-infected in a random sample collected from each plot. Four of the BAS 400 treatments significantly reduced the percent infected leaves over all other treatments evaluated. The BAS 500 @ 0.2 lb ai/A + the surfactant Penetrator Plus produced the highest level of control, with only 28.6 percent of the leaves in these plots having at least one white rust lesion, compared to 94.9 percent of the leaves in the check plots. When considering the treatment effect on the lesion severity, all treatments except Actigard @ 0.75 oz/A reduced percent infected area of infected leaves showing white rust symptoms. Actigard was also noted to cause some phytotoxicity in the form of upward leaf cupping.
Under the conditions of this study, the Ridomil Gold soil treatment did not appear to offer much toward reducing white rust infection . However, this data can be misleading. Previous work with metalaxyl (Ridomil) indicated efficacy from in-furrow soil treatments afforded approximately 40 days of control. Since the product is highly water soluble, not much Ridomil is available after this time. The 2000 - 2001 spinach season was unusually wet during the early half of the season. Therefore, it is logical to assume that most of the Ridomil Gold had been leached out of the soil long before white rust appeared as a problem. The initial white rust lesions were observed on January 4, 76 days after planting. In most seasons, the most severe white rust epidemics occur when early season infection is a problem. The Ridomil Gold soil treatment affords early season control. It would be unwise at this point in time to omit its use from a white rust disease-control program in Texas.
Another interesting result was seen in the data from this study: the effect of surfactant(s) on white rust infection. When Penetrator Plus was included with BAS 500, the level of control increased. In addition, the surfactants Activate, SDS, and Naiad reduced the percent infected leaves, as compared to the non-treated check, by 18.8, 11.9, and 11.4 percent respectively. These results suggest additional investigation of the merits of these types of products is warranted.
