Roberto Lopez and Kellie Walters, Department of Horticulture, Michigan State University-May 16, 2017
The air temperature and the alkalinity of the carrier water during application will affect the efficacy of ethephon plant growth regulator (PGR) application.
Plant growth regulators (PGR) are commonly used as foliar sprays, substrate infusions, lining infusions or bulbs, tubers and rhizomes infusions/infusions. Using plant genetic resources on greenhouse crops can help growers produce uniform and compact plants that can be easily packaged, transported, and sold to consumers. Most of the PGRs used by greenhouse growers (for example, pyrethroid, chlorergot, damazine, fluoxamide, paclobutrazol or uniconazole) inhibit stem elongation by inhibiting the biosynthesis of gibberellins (GAs) (Extended growth) Gibberellin is a plant hormone that regulates growth. And the stem is elongated.
In contrast, ethephon (2-chloroethyl; phosphonic acid) is a PGR that has many uses because it releases ethylene (a plant hormone responsible for maturation and senescence) when it is applied. It can be used to inhibit stem elongation; increase stem diameter; reduce apical dominance, leading to increased branching and lateral growth; and causing the shedding of flowers and buds (abortion) (photo 1).
For example, if used during reproduction, it can set the “biological clock” of sporadic or uneven flowering crops (such as Impatiens New Guinea) to zero by causing abortion of flowers and flower buds (photo 2). In addition, some growers use it to increase branching and reduce stem elongation of petunia (photo 3).
Photo 2. Premature and uneven blooming and reproduction of Impatiens New Guinea. Photograph by Roberto Lopez, Michigan State University.
Figure 3. Petunia treated with ethephon had increased branching, decreased internode elongation and aborted flower buds. Photograph by Roberto Lopez, Michigan State University.
Ethephon (for example, Florel, 3.9% active ingredient; or Collate, 21.7% active ingredient) sprays are usually applied to greenhouse crops one to two weeks after transplantation, and can be reused one to two weeks later . Many factors affect its efficacy, including ratio, volume, use of surfactants, pH of the spray solution, substrate humidity and greenhouse humidity.
The following content will teach you how to optimize the application of ethephon sprays by monitoring and adjusting two often overlooked cultural and environmental factors that affect efficacy.
Similar to most greenhouse chemicals and plant genetic resources, ethephon is usually used in liquid (spray) form. When ethephon is converted to ethylene, it changes from liquid to gas. If ethephon is decomposed into ethylene outside the factory, most of the chemicals will be lost in the air. Therefore, we want it to be absorbed by plants before it is broken down into ethylene. As the pH value increases, ethephon quickly decomposes into ethylene. This means that the goal is to maintain the pH of the spray solution between the recommended 4 to 5 after adding ethephon to the carrier water. This is usually not a problem, because ethephon is naturally acidic. However, if your alkalinity is high, the pH may not fall within the recommended range, and you may need to add a buffer, such as acid (sulfuric acid or adjuvant, pHase5 or indicator 5) to lower the pH. .
Ethephon is naturally acidic. As the concentration increases, the pH of the solution will decrease. As the alkalinity of the water carrier decreases, the pH of the solution will also decrease (photo 4). The ultimate goal is to keep the pH of the spray solution between 4 and 5. However, growers of purified water (low alkalinity) may need to add other buffers to prevent the pH of the spray solution from being too low (pH less than 3.0).
Figure 4. The effect of water alkalinity and ethephon concentration on the pH of the spray solution. The black line indicates the recommended water carrier pH 4.5.
In a recent study from Michigan State University, we used three water-carrying alkalinities (50, 150 and 300 ppm CaCO3) and four ethephon (Collate, Fine Americas, Inc., Walnut Creek, CA; 0, 250, 500 and 750) applied ethephon (ppm) concentration to ivy geranium, petunia and verbena. We found that as the alkalinity of the water carrier decreases and the concentration of ethephon increases, the ductility growth decreases (photo 5).
Figure 5. The effect of water alkalinity and ethephon concentration on the branching and flowering of ivy geranium. Photo by Kelly Walters.
Therefore, MSU Extension recommends that you check the alkalinity of the carrier water before using ethephon. This can be done by sending a water sample to your preferred laboratory, or you can test the water with a handheld alkalinity meter (Figure 6) and then make the necessary adjustments as described above. Next, add ethephon and check the pH of the spray solution with a handheld pH meter to make sure it is between 4 and 5.
Photo 6. Portable hand-held alkalinity meter, which can be used in greenhouses to determine the alkalinity of water. Photo by Kelly Walters.
We have also determined that the temperature during chemical application will also affect the efficacy of ethephon. As the air temperature increases, the rate of ethylene release from ethephon increases, theoretically reducing its efficacy. From our research, we found that ethephon has sufficient efficacy when the application temperature is between 57 and 73 degrees Fahrenheit. However, when the temperature rose to 79 degrees Fahrenheit, ethephon had almost no effect on elongation growth, even branch growth or flower bud abortion (photo 7).
Figure 7. The effect of application temperature on the efficacy of 750 ppm ethephon spray on petunia. Photo by Kelly Walters.
If you have a high water alkalinity, please use a buffer or adjuvant to reduce the alkalinity of the water before mixing the spray solution and finally reaching the pH value of the spray solution. Consider spraying ethephon sprays on cloudy days, early in the morning or evening when the greenhouse temperature is below 79 F.
Thanks. This information is based on work supported by Fine Americas, Inc., Western Michigan Greenhouse Association, Detroit Metropolitan Flower Growers Association, and Ball Horticultural Co.
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