Management of Fusarium oxysporum race 3 in processing tomatoes with chemical and biofungicides and cultivar resistance

Abstract

Fusarium wilt race 3 of tomato (Solanum lycopersicum), caused by the soil fungal pathogen Fusarium oxysporum f. sp. lycopersici race 3 (F3), has increased in both incidence and severity in the San Joaquin Valley, CA, production areas over the past decade. A limited number of chemical and biological fungicides (biofungicides) are registered and claim suppression of Fusarium. Trials were conducted in central California in 2016-17 to evaluate the efficacy of fungicides and biofungicides applied as transplant drenches on controlling F3 in resistant and susceptible processing tomato cultivars. The trials were located in commercial fields with low to severe levels of F3. Serenade Soil (Bacillus subtilis) and Regalia (extract of Raynoutria sachalinensis) biofungicides were applied at label recommended rates, equivalent to 10 L ha(-1). Fludioxonil (40.3%) and fluopyram (41.5%) fungicides were applied at rates equivalent to 0.41-0.82 and 0.25 kg a.i. ha(-1), respectively. Initial applications were made to the plants immediately before transplanting. Treatment design was a randomized block with 4 replications; Fisher’s protected LSD was used for comparison tests. Susceptible cultivars ‘H5608’ and ‘H8504’ had significantly (p<0.05) higher F3 infection as compared to the F3 resistant cultivars ‘BP16’ or ‘BP141’. Both fludioxomyl and fluopyram fungicides significantly reduced the number of Fusarium infected plants 70 days after planting in susceptible cultivars, but 50-93% were infected regardless of fungicide treatment at harvest. In 2017, yields increased approximately 21% with ‘H5608’ when fungicides were used. However, in 2016 the fungicide treatments increased yield for the resistant cultivar ‘BP141’. The biofungicides did not provide yield benefits nor suppressed the onset of Fusarium wilt in any year/location. Cultivar resistance, regardless of fungicide treatment, gave excellent suppression of F3 and good yield performance in fields with and without F3.