ASHS 2025 Conference

Obtaining sufficient nutrients and fighting foliar diseases caused by pathogens such as Alternaria and Cercospora remain an on-going problem for many carrot (Daucus carota) growers. Spraying leaves with mixtures containing soluble nutrient sources and beneficial microbes have potential to help address these issues, but the benefits may depend on the responsiveness of individual carrot genotypes. To test this hypothesis, a field trial was conducted on an organic farm in northern Indiana using three diverse carrot genotypes (Napoli, Nb3999, and Bolero). Each genotype was sprayed with a mixture of four commercial products commonly used by many organic farmers in the area, or left untreated as a control. Soil samples were collected midseason and changes in soil chemical and biological properties were quantified using standard practices. The incidence and severity of foliar diseases was also evaluated visually during the growing season and leaf samples were collected for quantification of leaf microbiomes. At harvest, total shoot and root biomass was determined and carrot taproot samples were collected for analysis of nutritional quality and endophytic microbiomes. Preliminary results indicated that foliar diseases were not particularly problematic during the 2024 growing on this farm. The carrot genotypes varied significantly with respect to above and belowground biomass, however, the treatments did not have any effect on these parameters. There were also no differences in the impact of the foliar sprays on soil parameters, which was expected. We suspect that the lack of any effect of the foliar sprays on carrot biomass was due to the absence of disease pressure at this site, where changes induced in leaf and root microbiomes could have helped mitigate any disease pressure.