The survival of Fusarium oxysporum f. sp. fragariae through soil fumigation

Authors: Henry, Peter; BOLDA, M - University Of California - Cooperative Extension Service; RAMOS, M - Non ARS Employee; GORDON, THOMAS - University Of California

Submitted to: Methyl Bromide Alternatives and Emissions Research Conference Proceedings
Publication Type: Other
Publication Acceptance Date: 11/14/2019
Publication Date: 11/14/2019
Citation: Henry, P.M., Bolda, M., Ramos, M., Gordon, T.R. 2019. The survival of Fusarium oxysporum f. sp. fragariae through soil fumigation. Methyl Bromide Alternatives and Emissions Research Conference, November 11-12, 2019, San Diego, California.

Interpretive Summary: Soil fumigation can kill plant pathogens that decrease yield. Strawberry growers routinely fumigate soil to control these pathogens. Recently, fumigation has not effectively controlled a fungal pathogen called Fusarium oxysporum f. sp. fragariae. We hypothesize that this pathogen is surviving on plant tissues that are not effectively treated by fumigation. We found that the pathogen could survive on strawberry crown tissues. These infested crown tissues are likely to lead to future disease. Some strawberry cultivars can be grown in the presence of the pathogen and not get diseased and are called “resistant”. Cultivars that are not resistant to the pathogen are susceptible. Susceptible cultivars suffered severe disease even after fumigation. There was no difference in yield between two different fumigation treatments when resistant cultivars were grown. This result was surprising, because only a strip tillage was done before planting for one of the treatments. This promising result suggests that reduced tillage could be economical in strawberry production and would reduce greenhouse gas emissions that occurs during field tillage.

Technical Abstract: We assessed the survival of Fusarium oxysporum f. sp. fragariae (cause of Fusarium wilt of strawberry) on strawberry crown tissues through flat fumigation with chloropicrin and crop termination with metam potassium. Survival of F. oxysporum f. sp. fragariae was not significantly different between two treatments: 10” buried crowns prior to flat fumigation (22% recovery) and living plants treated with metam potassium (25% recovery). Both of these treatments had significantly greater levels of disinfestation compared with 20” buried, flat fumigated plants or dead plants treated with metam potassium (65% and 66% mean survivorship, respectively). Two Fusarium-resistant (cv. San Andreas and cv. Fronteras) and two Fusarium-susceptible (cv. Monterey and cv. Cabrillo) cultivars were planted after fumigation to monitor yield and disease severity in the subsequent season. Beds were listed after flat fumigation with normal tillage practices. Only the beds were tilled after metam potassium treatment, which is a method of conservation tillage. Treatment did not have a significant effect on yield for any cultivar. Both susceptible cultivars had severe symptoms of Fusarium wilt and very low fruit production by the end of July. Therefore, neither treatment effectively reduced the impact of disease on a susceptible cultivar. In contrast, resistant cultivars continued to produce fruit throughout the season, with yield comparable to what was observed in previous years. Results of our study suggest that conservation tillage with crop termination can produce yields that are comparable to the grower standard at a fraction of the pre-plant cost. However, Fusarium-resistant cultivars are needed to achieve viable production with this approach in an F. oxysporum f. sp. fragariae-infested field. In addition to reducing pre-plant costs, no-till strawberry production eliminates the need for 10 or more tractor passes during tillage and bed shaping, which substantially reduces fossil fuel usage. Future trials are planned to test the generality of our results.