Ethephon Is A Cost-Effective Option For Improved Plant Structure, Preventing Early Flowering And Controlling Excessive Growth

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Ethephon has a long history of usage since its discovery almost 50 years ago and registration in 1973. It is one of the most widely utilized plant growth regulators in the world. The spectrum of agricultural usage includes fruit ripening in pineapple and tomatoes, the increase of hybrid seed production in cucumbers, squash and pumpkins, fruit elimination in ornamental trees and shrubs and removal of mistletoe from ornamental plants.

Concentration (ppm)
Florel (3.9 percent)
[Milliliters per 1 gallon]
Collate (21.7 percent)
[Milliliters per 1 gallon]
25021.73.9
50043.47.8
100086.815.6

In greenhouse floriculture production, Florel has been the go-to ethephon formulation for years. It is available as a 3.9 percent active ingredient solution from Monterey Chemical Co. and Southern Agricultural Insecticides, Inc. In 2013, Fine Americas introduced Collate, which is a higher 21.7 percent concentration of ethephon.

Greenhouse label uses include inducing flowering of ornamental bromeliads, avoidance of stem topple of potted hyacinths, height control of potted daffodils, flower inhibition, increase in axillary shoot development and height control. Many of the current uses of ethephon were the result of research conducted by Dr. Peter Konjoian in the 1990s.

With its extensive use in the greenhouse, it is beneficial to highlight some of the best management practices of ethephon in order for you to maximize its use and efficacy.

Protective Equipment And REI
First, let’s cover a few safety issues. Ethephon is a minor eye and skin irritant. Because of this, it has a longer restricted entry interval (REI) of 48 hours. In addition, it should be noted that eye protection is required, along with protective gloves, coveralls, apron, shoes and headgear for overhead applications.

Application
Ethephon is registered for use as a foliar spray. It cannot be applied through the irrigation system. Extensive university research trials have shown the suitability of ethephon as drench or pre-plant liner soak application, but currently neither option is on the label. Hopefully, labels will be updated in the future.

Application Parameters
Ethephon breaks down and becomes inactive with high water pH conditions greater than 6.1. While the registered ethephon products all contain acidifiers, in areas with high levels of alkalinity, the alkalinity will need to be neutralized before mixing the spray solution. The ideal endpoint pH for an ethephon solution is about 4.5 to 5.0.

In addition, ethephon activity is linked to active plant growth. Applications made when temperatures are below 60°F (15.5°C) or higher than 95°F (35°C) will be less effective.

Timing Applications
When used to promote axillary branching, the plants should be well rooted in the container. Typically, rooting to the side of the pot will occur within two weeks. For prevention of early flowering, it should be noted that the last application should be made six to eight weeks prior to the intended sales date. Late applications will result in flower delay. Some southern growers will also use ethephon as a flowering tool for geraniums by spraying 90 percent to hinder early flowering and thus avoiding the need to remove blooms. The remaining 10 percent are not sprayed and allowed to bloom in case the weather breaks early, and thus color will be available for early sales.

Suitable application windows should also be noted with stock plants. Ethylene can inhibit rooting, so applications should not be made within days of harvesting cuttings.

Avoid Applications To Stressed Plants
When used correctly, ethephon applications will result in enhanced plant growth. Because ethylene produced by ethephon is a stress enhancer, it is important to have the plants actively growing and not under suboptimal conditions (heat, drought, environmental or disease stress). Lower leaf yellowing typically occurs when ethephon is applied to water-stressed plants.

Optimal Concentrations
For most plants, spray rates are typically at 500 ppm. Complete spray coverage is required because ethephon is not translocated in the plant. This is especially important for plants such as garden mums. Incomplete spray applications will result in uneven growth and flowering. Research has shown that drench and pre-plant liner soaks application rates are less, in the range of 125 to 250 ppm.

Phytotoxicity
Some cultivars have a greater sensitivity to ethephon. Cupping and distortion of the young expanding leaves can occur. In addition, over-application can also result in distortion and leaf bleaching.

Comparison Trials
How do the two formulations compare? At North Carolina State University, we have conducted extensive trials comparing Florel and Collate. In our trials, both formulations had similar efficacies.

Ethephon is an excellent and cost-effective option for improving plant structure, preventing early flowering and controlling excessive plant growth. It is easy to see why Ethephon has become an essential component of the floriculture PGR toolbox.

Brian Whipker is a professor in the Department of Horticultural Science at North Carolina State University.

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