The effect of propagation substrate on Pythium root rot severity and the efficacy of biopesticides

Modern greenhouse crop production utilizes soilless substrates that range from inorganic substrates (Oasis foam and rockwool) to blends of organic substrates (sphagnum peat moss, coconut-fiber, bark mulch, wood chips, and wood products). Additionally, greenhouse growers utilize beneficial microorganisms in the form of commercial biopesticides to reduce disease. Few research studies have examined the effect of propagation substrate on the efficacy of commercial biopesticides under greenhouse production conditions. The objective of this study was to evaluate the effect of propagation substrates on commercially available microbial biopesticides (Rootshield WP, Cease, and Regalia) applied in propagation and at transplant for management of Pythium root rot. In this study, cucumber and calibrachoa were used as model crops. Over both cropping systems, plants propagated in Oasis foam had lower root rot compared to plants propagated in coconut coir. Across all biopesticide treatments, cucumber plants propagated in Oasis foam had 52% less root rot compared to plants propagated in coconut coir. In both infested and non-infested calibrachoa plants, plants propagated in Oasis foam had 45% to 67% less disease and plants propagated in peat had 25% to 40% less disease compared to plants propagated in coconut coir. There was no effect of biopesticide on Pythium root rot severity except for a reduction seen in calibrachoa plants propagated in coconut coir and treated with Rootshield WP. This research suggests that propagation substrate is important for root disease management.