It’s important for growers to know how media components can interact with the active ingredients of PGRs to reduce drench efficacy.
Growing media used in greenhouse production are commonly soilless mixes comprised of various proportions of organic components such as peat and bark, and inorganic components such as vermiculite and perlite. The question is – which media components affect the efficacy PGR drenches?
Research has shown that when bark, either fresh or composted, is included as a media component, it can reduce the efficacy of PGR drenches. Other components including peat, coir, perlite, and vermiculite have been shown to have little or no effect on the efficacy of PGR drenches.
A growing trend among growers is to identify more sustainable practices and products to incorporate into the greenhouse production of ornamentals. As part of this movement, there is a desire to identify alternative media components to replace limited organic components or inorganic components with energy-intensive manufacturing.
Parboiled rice hulls are an attractive media component for growers wishing to incorporate a sustainable product into their crop production. An agricultural by-product, rice hulls can provide aeration, are safe for employees to handle and work with, and are well-suited for composting or incorporation into the garden bed by the consumer.
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Parboiled rice hulls
Researchers at Purdue University identified the interaction between different media components and PGR drenches for the northern U.S. to control height or stem length of containerized bedding plants.
The group planted ‘Callie Deep Yellow’ calibrachoa and ‘Delta Orange Blotch’ pansies in 4.5-inch round pots filled with three different soilless media: peat and perlite (PP); peat and parboiled rice hulls (PRH); and peat and bark (PB). The plants were treated with 2.5-ounce drenches per pot of clear water or PGR solutions container Concise at 1 and 2 ppm (calibrachoa) and 0.5 and 1 ppm (pansy).
Plant height (pansy) or length of the longest stem (calibrachoa) was measured weekly and final measurements were made 6 weeks after treatment. There were no differences among pansies when treated with 0.5 ppm Concise across media. As Concise concentration increased to 1.0 ppm, height of pansies grown in PP and PRH media were similar, while plants grown in PB were taller. Similarly, when 0.5 or 1.0 ppm Bonzi drenches were applied plants grown in PP and PRH media had similar heights, while plants treated and grown in PB media were 4 to 6 in. and 2.5 to 3 in. taller, respectively.
Results with calibrachoa followed a similar trend. Stem length was 1 to 1.5 inches longer for plants grown in PB media compared to plants grown in PP and PRH media when 1.0 ppm Concise was applied. As Concise concentration increased to 2.0 ppm, stem length was similar regardless of media.
Growers who use media that contains bark will want to increase the concentration of PGR solutions. Growers who use a media containing rice hulls, and not bark, can adopt the drench strategies they currently use for crops grown in peat and perlite media. The researchers encourage growers to do on-site trials.
Contact Roberto Lopez (rglopez@purdue.edu) for more information.