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PGRs – The Importance of Volume by Paul Pilon

April 13, 2010

Plant growth regulators (PGRs) are chemicals that are primarily used to reduce stem elongation on various crops (containerized annuals, perennials, potted crops, and woody ornamentals) during production. PGRs, when they are applied properly, are very effective at controlling plant height and increasing the quality characteristics of the crops growers produce. PGRs help growers to produce more balanced and aesthetically pleasing plants, reduce shrinkage, increase crop uniformity, extend shelf life, and allow them to ship more plants per load.

Regardless of the plant growth regulator applied, the rates used and the results obtained will vary with climate, season, genetics, plant stage of development, application method, application volume, and the applicator. Besides using a PGR effective at reducing stem elongation of a given plant, the volume is the next most important factor growers must understand when using these products. The most important lesson that I can offer to growers regarding the use of PGRs is for them to understand the ‘Volume Effect’. Regardless of the application method used to apply PGRs, the volume of PGR solution applied has a greater affect on the results than does the concentration of the solution being applied.

Every commercially available PGR (products containing ancymidol, chlormequat chloride, daminozide, flurprimidol, paclobutrazol, and uniconazole) labeled for greenhouse and ornamental crops specifies in its label the recommended volume to apply for each of the various application methods. For example, with spray applications each label specifies growers apply 1 gallon of spray solution over 200 square feet of production space (2 quarts per 100 square feet). This is equivalent to 5 gallons of spray solution per 1,000 square feet or approximately 218 gallons per acre.

Working with a number of growers (small and large), I’ve come to realize that many of them are not aware of the actual spray volumes being applied with their PGR applications. In many instances, inadequate volumes are being applied which often results in unsatisfactory height control.

How does the volume applied affect the final results?

If a grower mixed a solution of uniconazole at 5 ppm and applied it at 1 quart per 100 square feet instead of the label’s recommendation of 2 quarts per 100 square feet, the outcome would essentially be equivalent to applying 2.5 ppm of uniconazole over the crops instead of the intended 5 ppm since half of the intended volume was applied.  Reducing the volume applied in half is like cutting the rate in half. A reduced spray volume will always reduce the effectiveness of the application resulting in a less than desirable level of height control. Additionally, several PGRs (flurprimidol, paclobutrazol, and uniconazole) are primarily absorbed through plant stems and in many cases sufficient coverage of the stems cannot be obtained with low spray volumes.

Conversely, if a grower mixed a solution of uniconazole at 5 ppm and applied it at 3 quarts per 100 square feet instead of the label’s recommendation of 2 quarts per 100 square feet, the outcome would result in an increase in the PGR rate and could possibly lead to excessive height control (severe stunting). In this example, increasing the volume by 50% is essentially equivalent to applying 7.5 ppm of uniconazole over the crops instead of the intended 5 ppm. Increasing the volume of the spray solution applied will always increase the effectiveness of the application which often results in a more than desired level of height control and may stunt crops, prolong the production period, and may render some crops unsalable.

These examples demonstrate that the effectiveness of PGRs is both a function of the rate and the volume being applied. Of these two variables, volume is the deciding factor and ultimately will determine if a grower’s application is successful or not.

Although the examples above focused specifically on PGR spray applications, the ‘Volume Effect’ also applies to other application methods. Growers must know what volume of PGR solutions they are applying for each application method in order to prevent over or under applications, both of which may lead to unsatisfactory results and in some cases unsalable plants. When used properly, plant growth regulators can make a big difference on crop production, plant quality, and your bottom line.

Paul Pilon
Perennial Solutions Consulting

The mention of specific active ingredients does not constitute an endorsement or recommendation of, or discrimination against similar products not mentioned.  ALWAYS READ PRODUCT LABELS AND USE PLANT GROWTH REGULATORS AS DIRECTED ON THE LABEL.


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