Getting The Most Out of Your PGR Applications

There are a number of factors that influence getting the most out of your plant growth regulator applications.  Some of the top considerations are listed below.

Environmental Conditions.  Environmental conditions can have a significant impact on the efficacy of a PGR.  Applying PGRs early in the morning or late at night when the evaporation rate is lower will allow for greater chemical uptake. After application, the PGR should be allowed to dry and wetting the leaves should be avoided.  Dazide should be allowed at least 4 hours before wetting the foliage, while most of the other PGRs only require 1 hour (Table 1).

A research trial conducted at NC State University investigated the effects of lightly rewetting the foliage 24 hours after the initial foliar spray.  We found that we were able to obtain 5 to 10% greater control than not rewetting the leaves.  The reason for this greater activity is because it allowed another opportunity for the PGR to be absorbed into the leaves.

Avoid Applying PGRs to Stressed Plants.  Plants should not be water stressed when PGRs are applied.  The risk of phytotoxicity increases with stress.  This is especially true with ethephon (Collate and Florel).  If the plants are stressed, lower leaf yellowing can result.

Check Plants.  How well does the PGR treatment really work?  The only way to confirm the efficacy of a PGR is to leave a few representative plants untreated.  These “check plants” offer a valuable insight into ways to adjust future PGR applications (Figure 1).

Dosage. The dose to apply to a crop is based on two factors:

  1. The solution concentration and
  2. Volume of solution applied per area.

Foliar sprays require an even application to obtain consistent results.  To accomplish this, a dose is based on:

  • Measuring out a known amount of chemical
  • Adding it to a known volume of water
  • Applying a spray to a known bench area.  Most foliar sprays are applied at the rate of 1 gallon per 200 square feet of bench area.

Drench applications are based on:

  • Measuring out a known amount of chemical
  • Adding it to a known volume of water
  • Applying a known volume of the drench to each pot or plant

The volume of drench applied increases with the pot size (specifics are listed on each product label).  For instance, 2 oz of drench solution should be applied to a 4-inch pot, 3 oz to a 5-inch pot, 4 oz to a 6-inch pot, and 10 oz to an 8-inch pot.

PGRs are an effective method of controlling excessive plant stretch.  Knowing how they work will enable you to improve your efficacy.

Table 1. Recommended Leaf Wetness Time to Maximize Uptake
Chemical PGR Name Chemical Absorption (hours)
Ancymidol Abide 0.5-1.0
Chlormequat chloride Citadel 4
Daminozide Dazide 18-24
Ethephon Collate 12-16
Flurprimidol Topflor 0.5-1.0
Paclobutralzol Piccolo, Piccolo 10XC 0.5-1.0
Uniconazole Concise 0.5-1.0



Figure 1.  One poinsettia with the bamboo stake was left as an untreated control in order to evaluate the effectiveness of the plant growth regulator treatment.