2018 ASHS Annual Conference
Effects of Pine Bark Substrate Age on Paclobutrazol Efficacy and Growth Control in Marigold
Effects of Pine Bark Substrate Age on Paclobutrazol Efficacy and Growth Control in Marigold
Friday, August 3, 2018
International Ballroom East/Center (Washington Hilton)
Previous research has shown that pine bark as a horticultural substrate can reduce the efficacy of drench applied plant growth regulators (PGR). There is however no understanding or evaluation of the effect of pine bark age on substrate interaction with PGRs. Physical and chemical characteristics of pine bark have been shown to change significantly over time during the aging or composting process. Therefore, the efficacy of PGRs in substrates containing pine bark may be affected by the age of the pine bark used. To address this question, Paclobutrazol drench applications of 0, 1, 2, and 4 mg were applied to ‘Antigua Yellow’ marigold (Tagetes erecta) grown in 1L plastic containers filled with a 2:2:1 (v:v:v) peat: pine bark: perlite substrate. The pine bark of various ages was obtained from a commercial bark supplier. Bark substrates obtained and used in this study were 0, 3, 6, 9, and 12 months old. After six weeks, plant height, growth index, and dry weights were recorded. There was an interaction between PGR rate and bark age for marigold growth indices but not for plant height and dry weight. Marigold height increased when grown in substrates containing 6 month aged bark and was similar in 9 and 12 month aged bark as well. Plant dry weights increased as pine bark age increased from 0 to 12 months. These results indicate that pine bark age does affect marigold growth but the interaction between pine bark age and paclobutrazol efficacy was inconclusive.