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Douglas Bailey, Professor, and Brian Whipker, Extension Horticulture Specialist - page 3 / 16





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An example is a Bonzi soak, which is labeled as a preplant treatment for freesias.

Dosage: Read the label; do not guess on dosage. Keep in mind that a dosage is the product of concentration of solution applied and volume of solution applied per area. If either are incorrect, results could be unpredictable and nonrepeatable. Take care to always apply the correct dosage to all plants treated.

Application Technique: As with the target tissue, the method of delivering a PGR depends on both the chemical used and the plant species to be treated. Table 1 lists labeled application techniques for PGR’s in the application method and rates column.

Dips: With some plants it is possible to dip the plant shoot, or underground portion (bulb, corm, tuber) into a growth retardant solution prior to potting. This method is labeled and is very effective for applying B-Nine to the shoots of rooted chrysanthemums just prior to potting. This method is fairly accurate, if each plant remains in the solution for the same amount of time, and if each plant has approximately the same size shoot or bulb. Unfortunately, this method is not feasible with many crops, and dipping plants in a common solution could result in the spread of disease organisms.

Drenches: Applying a growth retardant in a drench form is fairly easy. Measure out a known amount of chemical, add it to a known volume of water, and apply a known volume of the drench to each pot or plant. As pot size increases, usually the volume of drench recommended also increases. If using a drench, make sure the volume and concentration of the solution are correct for the size pot to be treated. There are “drenching machines” available on the market that emit a set volume of drench then turn off for a short period of time prior to the next dose to allow applicators to place the nozzle into the next pot to receive the drench. Do not apply any plant growth regulator through an irrigation system, unless the label lists chemigation as a legal application technique. Currently, it is legal


to apply A-Rest through drip, overhead boom, sprinkler, and flood (subirrigation) systems. Consult the label for specific application recommendations.

Sprays: A spray application can be more difficult to apply evenly than a drench, but with attention to detail, is the method of choice. Some chemicallabels recommendto “spraytorunoff”; that is, spray each plant until spray visibly just begins to drip off of the foliage. Depending on the size of the plant, the sprayer’s objectivity, and other factors, varying amounts of chemical will be applied to each plant. It is much safer and more accurate to base spray application on areas, not plants. Apply a known volume of spray evenly to a known area (square footage), regardless of how many plants are in that known area. The general recommendation for sprays is to apply 1/2 gallon per 100 ft2 of cropping area. This volume is sufficient to comfortably walk 25 feet while spraying a 4 foot-wide bench, thus the basis for the recommendation. If the area is sprayed evenly, it assures that each pot will receive the same amount of spray, regardless of how many containers are in the area.

To help with uniform distribution, the sprayer should be equipped with a pressure gauge and pressure regulator to assure uniform output. Unless the sprayer is emitting a constant volume, spray will not be applied evenly over plants.

Spray droplet size can affect spray distribution on the plants. In general, the smaller the droplet size, the more even the coverage and the greater the effectiveness (efficacy) of the chemical. Therefore it is possible that two growers applying the same treatment but with different spray nozzles could achieve different degrees of effectiveness. For consistency, try to use the same nozzle type for all PGR applications.

Spray adjuvants, compounds added to assist the action of the active ingredient, such as a wetting agent can affect PGR efficacy. Some PGR products such as A-Rest, Bonzi, and Sumagic advise against adding a wetting agent. B-Nine already contains a wetting agent and may

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