Effect of aerobic compost tea inputs and application methods on protecting tomato from Phytophthora capsici

Numerous challenges exist in organic tomato production, one of the largest being a lack of amendments that can effectively serve as crop nutrients or pest controls and still be considered organic. Compost is a recognized organic input, and a recent development is the use of compost tea in fertility and biocontrol applications. Aerobic compost tea (ACT) is produced by aerating compost and water and allowing microbial activity to increase over a few days. An investigation into the biocontrol and fertility efficacy of different ACT formulations, as well as ACT crop application methods was completed. Four batches of ACT, two based on Sustane (commercial compost from poultry litter) and two based on spent mushroom compost, with or without nutritional additives, were made at a ratio of 31:1 water to substrate. In vitro antifungal bioassays revealed that all Sustane and spent mushroom compost ACTs reduced the growth of Phytophthora capsici whereas only ACT based on spent mushroom compost reduced the growth of Botrytis cinerea. A greenhouse trial using the tomato cultivar ‘Glamour’ was completed and ACT was applied by spraying the shoots or drenching the potting mixture either pre-inoculation or pre- and post-inoculation with P. capsici. All ACTs reduced disease progress although there were differences across application methods. Generally, drenching ACT reduced disease more than spraying and applying ACT twice (before and after pathogen inoculation) was also better than applying ACT once before inoculation. The percent reduction in disease progress ranged from an average of 6.4% for spraying ACT once to an average of 73.4% for drenching ACT twice. This same trend was observed in the plant biomass data. In addition, the biomass data suggests that ACT also offered fertility benefits to the tomato plants. ACT therefore holds promise as a sustainable biocontrol treatment as well as a source of plant nutrients for organically grown tomato.