Calculating Costs Part II: PGRs

May 16, 2006 - 12:29

PGRs include naturally occurring compounds (referred to as plant hormones) as well as synthetic compounds. The most common PGRs used on floricultural crops are listed in Figure 1, right. This article will focus on PGRs that both promote or retard growth.

Application Methods

There are several methods for applying PGR solutions: 1) spraying the foliage and stems (foliar sprays); 2) drenching the growing medium; 3) dipping rooted or unrooted cuttings; 4) soaking rhizomes, tubers, bulbs or other storage organs; and 5) spraying the growing medium surface prior to potting.

PGR labels provide detailed information on the crops that can be treated and application methods that are appropriate for each crop. All of the common PGRs can be applied as foliar sprays (see Figure 2, page 48), but some application methods are more restricted. Sumagic (Valent U.S.A. Corporation), for example, is the only PGR listed in Figure 2, page 48, that is labeled for pre-plant Á application to the growing medium surface prior to planting, and this method is labeled for use only on bedding plants.

Many growers prefer spray applications instead of drenches because large numbers of plants can be treated in a shorter period of time, so sprays are more economical in terms of labor costs. However, with drenches, the amount of active ingredient applied per pot is more consistent than with sprays (assuming the grower is careful to apply the same drench volume to each pot), so a more uniform PGR response can be obtained with drenches compared to sprays.

Calculating Spray Volume

This formula can be used to calculate the total volume of diluted PGR solution needed for sprays:

# gallons needed = Total # of square feet to be treated ÷ Coverage (square feet treated per gallon)

Generally for sprays, 1 gal. of diluted PGR solution is applied to every 200 sq.ft. of growing area. However, PGR manufacturers vary in their recommended rates (see Figure 3, page 50).


Example 1.
A grower is producing bedding plants in 806-cell packs in 1020 trays. The bedding plants are growing on 10 5x60-ft. benches. Determine the amount of B-Nine (Chemtura Corp.) solution needed for a spray application on the bedding plants.

1. List all variables to find out what is known and unknown:

  • 10 5x60-ft. benches of bedding plants.
  • PGR: B-Nine.
  • Recommended application rate for B-Nine sprays:

    1 gal. per 200 sq.ft. (Coverage = 200 sq.ft per gal.).

  • Number of gallons of diluted B-Nine solution is unknown.

2. Perform calculations:

  • # gallons needed = # square feet treated ÷ Coverage (square feet per gallon)
  • # gallons needed = 10 benches x 5 ft. x 60 ft. ÷ 200 sq.ft. per gal.
  • 3,000 sq.ft. ÷ 200 = 15 gal. of diluted B-Nine solution needed


Example 2.
A grower has 20 5x15-ft. benches of bedding plant plugs. Determine the amount of Bonzi (Syngenta Professional Products) solution needed for a spray application on the plugs.

1. List all variables to find out what is known and unknown:

  • 20 5x15-ft. benches of bedding plant plugs.
  • PGR: Bonzi.
  • Recommended rate for applying Bonzi as a spray on bedding plant plugs: 1 gal. per 200-400 sq.ft. Assume 1 gal. will be applied per 400 sq.ft. (Coverage = 400 sq.ft per gal.).
  • Number of gallons of diluted Bonzi solution is unknown.

2. Perform calculations:

  • # gallons needed = # square feet treated ÷ Coverage (square feet per gallon)
  • # gallons needed = 20 benches x 5 ft. x 15 ft. ÷ 400 sq.ft. per gal.
  • 1,500 sq.ft. ÷ 400 = 3.75 gal. of diluted Bonzi solution needed

Calculating Drench Volume

Use this formula to calculate the total volume of diluted PGR solution required for drenches:

  • # gallons needed = # pots x drench volume per pot ÷ 128 fl.oz. per gal.

Recommended drench volumes per pot are similar for most PGRs but differ slightly for Cycocel (OHP) (see Figure 4, page 50).



Example 3.
A grower has 3,000 6-inch pots of poinsettias and wants to apply Bonzi as a drench for height control. How many gallons of diluted Bonzi solution are needed for the poinsettias?

1. List all variables to find out what is known and unknown:

  • 3,000 6-inch pots of poinsettias.
  • PGR: Bonzi.
  • Recommended drench volume for Bonzi: 4 fl.oz. per pot (see Figure 4, page 50).
  • Number of gallons of diluted Bonzi solution is unknown.

2. Perform calculations:

  • # gallons needed = # pots x drench volume per pot ÷ 128 fl.oz. per gal.
  • # gallons needed = 3,000 pots x 4 fl.oz. per pot ÷ 128
  • 12,000 fl.oz. ÷ 128 = 93.8 or approximately 94 gal. of diluted Bonzi solution needed

Preparing Diluted Solutions

PGR recommendations typically come with a dilution table for each PGR. The dilution tables list the parts per million (ppm) of active ingredents and the corresponding amount of PGRs (in fluid ounces or milliliters) required to prepare 1 gal. (or liter) of diluted solution. The method I use for calculating diluted solutions does not require dilution tables but instead utilizes a single formula applicable for all PGRs. All the grower needs to do is plug in the desired concentration (in ppm) and the final volume of diluted solution and calculate the amount of PGR:

Amount of PGR = Desired concentration (ppm) x Final volume (gallons) ÷ Conversion constant

The conversion constants are specific for each PGR and listed in Figure 5, page 51. There are two conversion constants for each PGR: one for fluid ounces per gallon and the other for milliliters per gallon.
Example 4. Determine the number of fluid ounces of Cycocel required for a 1,000 ppm spray on geranium seedlings if 25 gal. of diluted PGR solution will be prepared.

1. List all variables to find out what is known and unknown:

  • 1,000 ppm Cycocel to be applied as a foliar spray.
  • 25 gal. of diluted Cycocel solution needed.
  • Conversion constant is 922 (see Figure 5, page 51).
  • Number of necessary fluid ounces of Cycocel is unknown.

2. Perform calculations:

  • Amount of PGR = Desired concentration (ppm) x Final volume (gallons) ÷ Conversion constant

Amount of PGR = 1,000 ppm x 25 gal. ÷ 922

25,000 ÷ 922 = 27.1 or approximately 27 fl.oz. of Cycocel needed

Example 5. The grower in Example 3 with 3,000 poinsettias in 6-inch pots will be applying Bonzi as a drench. The recommended rate for drenching poinsettias with Bonzi is .25-3 ppm; the grower chooses to apply 1.5 ppm. How many milliliters of Bonzi will be needed if 94 gal. of diluted solution will be prepared?

1. List all variables to find out what is known and unknown:

  • 1.5 ppm Bonzi to be applied as a drench.
  • 94 gal. of diluted Bonzi solution needed.
  • Conversion constant is 1.06 (see Figure 5, page 51).
  • Number of milliliters of Bonzi is unknown.

2. Perform calculations:

  • Amount of PGR = Desired concentration (ppm) x Final volume (gallons)÷ Conversion constant

  • Amount of PGR = 1.5 ppm x 94 gal. ÷ 1.06
  • 141 ÷ 1.06 = 133 ml of Bonzi needed

Example 6. A grower has 1,600 Easter lilies growing in 6-inch pots. The recommended rate for Sumagic applied as a drench on Easter lilies is .25-.5 ppm. How many gallons of diluted Sumagic solution are needed to drench the lilies, and how many fluid ounces of Sumagic will be needed if the application rate is .5 ppm?

1. List all variables to find out what is known and unknown:

  • 1,600 6-inch pots of Easter lilies.
  • .5 ppm Sumagic to be applied as a drench.
  • Recommended drench volume for Sumagic: 4 fl.oz. per 6-inch pot (see Figure 4, page 50).
  • Number of gallons of diluted Sumagic solution is unknown.
  • Number of fluid ounces of required Sumagic is unknown.
  • Conversion constant is 3.91 (see Figure 5, right).

2. Perform calculations:

  • # gallons needed = # pots x drench volume per pot ÷ 128
  • # gallons needed = 1,600 pots x 4 fl.oz. per pot ÷ 128
  • 6,400 ÷ 128 = 50 gal. of diluted Sumagic solution needed
  • Amount of PGR = Desired concentration (ppm) x Final volume (gallons) ÷ Conversion constant

  • Amount of PGR = .5 ppm x 50 gal. ÷ 3.91
  • 25 ÷ 3.91 = 6.4 fl.oz. of Sumagic needed to prepare 50 gal. of diluted solution

About The Author

Thomas Boyle is a professor in the Department of Plant, Soil & Insect Sciences at the University of Massachusetts. He can be reached at tboyle@pssci.umass.edu or (413) 545-3586.

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