Effect of chemical alternatives to methyl bromide on soil-borne disease incidence and fungal populations in Spanish strawberry nurseries: A long-term study.

Abstract

Chloropicrin (PIC) mixtures of 1,3-dichloropropene and chloropicrin (DD:PIC), dazomet, and metam sodium (MS) have been applied as chemical alternatives to methyl bromide (MB) in Spanish strawberry nurseries since MB was banned as a soil fumigant in 2005. These chemical alternatives were applied to soil in two Spanish strawberry nurseries between 2003 and 2017 to test their efficacy against the main crown and root disease and soil fungal populations in comparison with the use of MB and PIC (MB:PIC). These chemicals were applied at several doses with different application methods under plastic films. Crown and root disease incidence was calculated as the percentage of plants with symptoms caused by soil-borne pathogens. Soil fungal populations were estimated as colony forming units per gram of dry soil. All chemicals significantly reduced soil-borne fungal disease incidence and fungal population in both nurseries over the years. Phytophthora cactorum and Fusarium spp. were the main pathogens causing soil-borne diseases, followed by Verticillium spp. MB:PIC remained the treatment that best controlled P. cactorum. MS and DD:PIC controlled Fusarium disease to a lesser extent than MB:PIC and dazomet in both nurseries. MB:PIC and PIC were the two treatments that most reduced Verticillium spp. The population of Verticillium spp. declined and the presence of other species such as Colletotrichum spp. and Rhizoctonia spp. was minimal during the study. Chemicals are necessary to obtain healthy strawberry plants. The use of chemical alternatives to MB has resulted in changes in the incidence of soil-borne diseases and soil fungal populations in strawberry nurseries. Dazomet was an effective alternative to MB as a soil-borne disease control, except against Verticillium spp. MB alternatives in strawberry nursery soils have caused Fusarium spp. to displace Verticillium spp.