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Research Project: Sustainable Production and Pest Management Practices for Nursery, Greenhouse, and Protected Culture Crops

Location: Application Technology Research

Title: Paclobutrazol residues in recirculated water in commercial greenhouses

item RAUDALES, ROSA - University Of Connecticut
item TORO-HERRERA, MAYRA - University Of Connecticut
item FISHER, PAUL - University Of Florida
item Boldt, Jennifer
item Altland, James

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2024
Publication Date: 3/20/2024
Citation: Raudales, R.E., Toro-Herrera, M.A., Fisher, P., Boldt, J.K., Altland, J.E. 2024. Paclobutrazol residues in recirculated water in commercial greenhouses. HortTechnology. 34(2):198-203.

Interpretive Summary: Reusing irrigation water in greenhouses has many benefits. However, there are risks of recirculating fertilizers, agrochemicals, and pathogens throughout a facility. Paclobutrazol is a widely-used plant growth regulator in commercial greenhouse production to manage plant size. Its presence in recirculated water may have unwanted growth effects on crops if growers are unaware of residual concentrations. Water samples were collected from commercial growers using paclobutrazol to manage the growth of flowering plants. Residual concentrations of paclobutrazol were present in all facilities evaluated, and they correlated with application frequency and volume. These results suggest that growers should monitor residual paclobutrazol concentrations in recirculating systems and adjust future applications to account for residual low doses supplied by the irrigation water. Additionally, growers should consider remediation strategies if paclobutrazol levels exceed a target threshold for their facility, based on the sensitivity of crops being grown.

Technical Abstract: Reusing irrigation water has technical, environmental, and financial benefits. However, risks are also associated with the accumulation of agrochemicals, in addition to ions, plant and food safety pathogens, and biofilm organisms. In this project, we measured the concentration of paclobutrazol (a persistent and widely-used plant growth regulator) in recirculated water in greenhouses producing ornamental plants in containers. We collected solutions from catchment tanks at nine commercial greenhouses across seven states in the United States in spring and fall 2014. Paclobutrazol was detected in all samples, with differences observed by season, greenhouse operation, paclobutrazol application method, and irrigation method. Across operations, paclobutrazol was 31 times higher in spring (the peak production period for most ornamental greenhouses) compared with fall. High-volume applications to both foliage and substrate (“spray-drench"), followed by substrate only (“drench”) applications resulted in the highest residual concentrations in recirculated water. Our results indicate that paclobutrazol is likely to be a growth retardant risk in greenhouse operations recirculating water via irrigation of contaminated water to subsequent crops. A clear understanding of the risks associated with recirculated water intends to support the development and implementation of risk management strategies to ensure and promote safe use of recirculated water in greenhouses.