Inhibiting Growth of Flowering Crops with Ancymidol and Paclobutrazol in Subirrigation Water

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  • 1 Department of Environmental Horticulture, University of Florida, Gainesville, FL 32611-0670

Contamination of recirculated subirrigation water with growth retardants poses a potential problem for growers. Eight concentrations of ancymidol or paclobutrazol ranging from 0 to 100 μg·L-1 (0 to 1000 μg·L-1 for petunia) were supplied constantly in subirrigation water to potted plants to identify critical levels at which plant growth is affected. Concentrations of ancymidol resulting in 20% reduction in plant size relative to untreated controls were 3, 10, 98, 80, and 58 μg·L-1 for Begonia ×semperflorens-cultorum Hort. `Gin', chrysanthemum (Dendranthema ×grandiflora Kitam.) `Nob Hill', Impatiens walleriana Hook f. `Super Elfin Coral', Petunia ×hybrida Hort. Vilm.-Andr. `Madness Pink', and Salvia splendens Sell ex Roem. & Schult. `Red Hot Sally', respectively. Respective values for paclobutrazol were 5, 24, 17, 390, and >100 μg·L-1. The results provide useful information for managing potential growth retardant contamination problems or for applying growth retardants in subirrigation water. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); (±)-(R*,R*)-β-[(4-chlorophenyl)methyl]-α-(1,1-dimethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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