Reduction of Gray Mold with Preharvest Applications of Potassium Tetraborate in Greenhouse Tomato

Potassium tetraborate tetrahydrate, K2B4O7⋅4H2O (PTB), was assessed as a preharvest spray in the greenhouse for reducing gray mold of tomato fruit caused by Botrytis cinerea. Efficacy of PTB was compared with a natural proprietary product formulated by Agrichem, which was previously shown to inhibit mycelial growth of B. cinerea in vitro and was used as a positive control for greenhouse studies. Mycelial growth and spore germination of B. cinerea were completely inhibited in vitro by PTB at 25 mM. Phytotoxicity was not observed on treated tomato plants with PTB at 25 mM. Preharvest sprays were applied at three ripening stages: turning, pink, and light red. After fruit reached the final ripening stage, all fruits were harvested and stored for 10 days at either 4 or 25°C. Disease severity was reduced compared with controls after storage at either temperature when PTB was applied at the turning stage. Preharvest applications of PTB improved the marketable quality of postharvest tomato fruit and significantly reduced the incidence of gray mold in comparison with inoculated control plants, which received no preharvest fungicidal treatment.