Plant Growth Regulators for Greenhouse Crops
Active Plant Growth Regulator Ingredients
Before selecting a PGR, the greenhouse manage needs to understand the active ingredient (AI) in each chemical in managing greenhouse crop production. The AI is the compound in the product that can be used to increase or retard plant height, prolong or break dormancy, prolong flower and plant shelf-life, prevent leaf yellowing, abort flowers, or promote rooting, branching and/or flowering.
Ancymidol
Ancymidol can be applied to bedding plants, bulbs, chrysanthemums, Easter lilies, plugs, poinsettias, and foliage plants. Ancymidol is widely used as a foliar spray for treatment of plants in the plug stage. Its relatively high activity and toning ability produces excellent plugs. Many growers consider ancymidol to be the product of choice for pansy production. Growers often prefer the use of ancymidol on plugs because of its lack of phytotoxicity and because its limited residual allows the plugs to grow out of the growth control effects after being transplanted, thus making it a safer PGR to apply.
Benzyladenine
This AI is a synthetic cytokinin that promotes cell division, cell differentiation from undifferentiated tissues and inhibits dominant growth of the apical meristem, which promotes axillary shoots (branching). Benzyladenine stimulates, but does not cause, an increase in branching. Therefore, timing of the application is critical to a good branching response. Benzyladenine has been very effective in improving branching in both plugs and finished plants of many herbaceous perennial crops.
Chlormequat Chloride
This active ingredient is a gibberellin inhibitor, which reduces internode elongation for a more desirable, compact plant. It is used to reduce stem elongation. Like daminozide, chlormequat chloride is a forgiving PGR that will require multiple applications. In greenhouse crops, it is most commonly used on azaleas, bedding plants, geraniums, hibiscus, poinsettias, osteospermum and to other herbaceous and woody plants.
Daminozide
Used exclusively as a foliar spray, this AI is well absorbed into leaves and also a gibberellin inhibitor, which reduces internode elongation for a more desirable, compact plant. Daminozide can be applied to azaleas, bedding plants, chrysanthemums, gardenias, hydrangeas, poinsettias, and to other flowering and foliage plants except lilies.
Dikegulac Sodium
Dikegulac sodium is a compound that delays terminal growth by interfering with cell-wall synthesis, which is required for new growth. By primarily inhibiting terminals, apical dominance is reduced, which enhances the production of lateral branches. In addition to creating a fuller plant, enhancing the number of laterals in a pot generally reduces the overall height of the plant due to the greater distribution of resources.
Ethephon
Ethephon can be applied to azaleas, chrysanthemums, geraniums, lantana, petunia, and verbena varieties to increase lateral branching; control height and stem topple in bulb crops, specifically, Hyacinths and Narcissus; and delay flowering or abscise (abort) flower buds. Ethephon is only registered for foliar spray applications. Slight phytotoxic chlorosis (yellowing) may occur.
Flurprimidol
Flurprimidol can be applied to bedding plants and plugs, bulb crops, chrysanthemums, geranium, poinsettias, herbaceous perennials, and other flowering and foliage plants. Flurprimidol can be applied as a foliar spray or substrate drench to control plant height, thus resulting in compact plants.
Gibberellins
An application of this strong growth regulator will elongate plant cells. Gibberellin such as GA3 can be applied azalea, chrysanthemums, fuchsia, geraniums, lantana, and poinsettias.
Paclobutrazol
Paclobutrazol can be applied to bedding plants, bulb crops, flowering and foliage crops, and herbaceous perennial and woody ornamental plants. Paclobutrazol can be applied as a foliar spray or substrate drench to control plant height and width, thus resulting in compact plants.
Uniconazole
This AI inhibits the gibberellin biosynthesis. It is rapidly absorbed through the root, stem and leaf, and then transported to the meristem from the xylem. Uniconazole can be applied to bedding plants, bulb crops, chrysanthemums, Easter lilies, geraniums, poinsettias, and other herbaceous and woody plants. Uniconazole is most commonly used on herbaceous perennials.
Benzyladenine/Gibberellin Combination
The combination of benzyladenine + gibberellin such as BA+GA4+7 can be applied to Asiatic, Easter and LA lilies to avoid of reduce lower leaf chlorosis and leaf drop.
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