Efficacy of chloropicrin application by drip irrigation in controlling the soil-borne diseases of greenhouse pepper on commercial farms in Poland

Three demonstration experiments were conducted on commercial greenhouse farms to assess the efficacy of chloropicrin (CP), applied by drip irrigation, in controlling Verticillium wilt and root rot disease complex of bell pepper, in comparison with dazomet at 40 g m⁻². Chloropicrin was applied through drip irrigation system at 20, 30 and 40 g m⁻² of emulsified commercial formulation. The concentration of CP in water was constant, and the required doses were obtained by delivering different amounts of the irrigation water per area unit (from 12.5 to 33 mm). The highest mean efficacy in reducing the inoculum density of Verticillium dahliae in the soil at all locations was obtained after CP application at 30 and 40 g m⁻², about 85 and 86%, respectively. The number of viable microsclerotia recovered from the soil on the day of pepper planting was significantly correlated with the final incidence of Verticillium wilt disease (r = 0.962). The highest mean efficacy in controlling Verticillium wilt of pepper (86.4%) was obtained after soil treatment with CP at 40 g m⁻², and ranged from 80.2 to 95.6%. The yield was stronger correlated with root rot severity (r = −0.849**) than with progression of Verticillium wilt, expressed by AUDPC (r = −0.651**). The dominant soil-borne pathogen responsible for pepper root rot was Colletotrichum coccodes. All chemical treatments provided a significant reduction in root rot severity compared to the untreated control. On-thefarm evaluation revealed that soil fumigation with drip-applied chloropicrin presents a feasible option for pepper growers.