2013 ASHS Annual Conference

A study was conducted to evaluate the effects of two plant growth regulators (PGRs), paclobutrazol, on potted sunflower (Helianthus annuus L.) and zinnia (Zinnia elegans Jacq.), and ancymidol, on marigold (Tagetes erecta L.), zinnia (Zinnia elegans Jacq.), impatiens (Impatiens walleriana Hook.f.), and petunia (Petunia hybrida Vilm.) plugs, on water use and growth control. Paclobutrazol was either applied as a drench at 0, 1.0, 2.0, or 4.0 mg per pot of active ingredient for sunflower, or 0, 0.5, 1.0, or 2.0 mg per pot for zinnia, while ancymidol was applied at 0, 40, 80, or 160 mg·L^-1 as a foliar spray. With an increase in paclobutrazol dose or ancymidol concentration, plant growth (fresh weight, dry weight, plant height and diameter) and total water use was lowered for all species tested. For potted sunflower, 2.0 mg of paclobutrazol resulted in 31.5% less water uptake compared with nontreated plants. For potted zinnia, plants treated with 1.0 mg paclobutrazol utilized 45% less water. For plugs, a foliar application of ancymidol at 80–160 mg·L^-1 lowered water use by 1% to 7% for marigold, 10% to 18% for zinnia, 6% to 15% for impatiens, and 17% to 25% for petunia. In summary, application of plant growth regulators not only controlled excessive plant growth, but also lowered water uptake by the plants and increased water use efficiency for potted plants. These results demonstrate that using plant growth regulators should be considered a best management practice for controlling excessive plant growth and improving water use efficiency.