Product Overview

Topflor Plant Growth Regulator is one of the most versatile PGRs available. Topflor has the strength to regulate vigorous species yet provides the proper amount of growth control for slower growing crops. Though Topflor is most active via root uptake, it can be effectively utilized as through foliar sprays. As a result, drench applications of Topflor are more economical than many other PGRs.

Topflor treated plants exhibit little-to-no delay in blooms. In fact, most plants treated with Topflor display a more vibrant flower as well as darker green foliage. The compact growth resulting from Topflor applications strengthen and tones the plants increasing their tolerance to pest, environmental and shipping stresses.

Multi-site absorption
Excellent activity utilizing spray, drench and pre-plant soak applications
Little-to-no flower delay
Reduce production time and help meet shipping deadlines
Provides the perfect amount of growth regulation to a wide range of bedding, annual and perennial plants, bulb crops and woody ornamentals
Improves plant health
Higher tolerance to pests and environmental stresses
Topflor Liquid Quick Facts
Use Sites
Greenhouses/Shadehouses, Outdoor Nurseries
Ornamentals such as bedding plants, herbaceous plants, perennials, container ornamentals and shrubs
Recommended Rate
Spray, drench and chemigation
Restricted-Entry Interval (REI)
12 hours
Active Ingredient
Mode of Action (PGR Class)
Gibberellic acid biosynthesis inhibitor (Class B)

Labels and SDS

Specimen Label

Safety Data Sheet

Registered States

How Topflor Works

Topflor effectively reduces internode elongation through the inhibition of gibberellic acid (GA) biosynthesis, resulting in a more desirable plant. The active ingredient in Topflor, flurprimidol, is a nitrogen-containing heterocycle compound of the pyrimidine chemical class. Flurprimidol acts as an inhibitor of enzymes catalyzing the steps in the GA biosynthetic pathway that involve oxidation of ent-kaurene to ent-kaurenoic acid, a GA precursor.

Topflor has been shown to increase the quality of plants, even in the absence of growth reduction. Some of these desirable qualities include enhanced leaf and bloom color, higher chlorophyll content, greater leaf thickness, stronger stems, and decreased water loss.

Topflor is a 0.38% formulation containing 14.4 grams of flurprimidol per gallon of product.

Topflor has a Caution label with a low 12-hour re-entry interval (REI). Required personal protective equipment (PPE) includes: coveralls, chemical-resistant gloves made of any waterproof material, long sleeved shirt and pants, and shoes plus socks.

Factors that influence Topflor efficacy

Cultivars or varieties within a given plant species may respond differently to Topflor. Varieties that are taller or more vigorous generally require more Topflor than naturally short or less vigorous varieties. Stage of plant growth at the time of application will also influence the amount of Topflor needed.

Environmental conditions can also strongly influence the response to Topflor and, therefore, the amount of product applied. Growers in warm climates may need to use higher rates and/or more applications compared to those in cooler climates. The Topflor rate, as well as number of applications, may also vary depending on the time of year, with higher rates and/or more applications needed during warmer months.

Cultural practices may affect the plant's response to Topflor. Plants that are grown at close spacing or in small pots and using high water and fertility levels may require higher rates of Topflor to achieve the desired response. The effectiveness of a Topflor drench may be reduced in root media that utilizes a high amount of pine bark. Another factor that influences the amount of Topflor required for an optimum growth response is application method (spray or drench) and technique including the uniformity of coverage and degree to which the spray solution is allowed to run off the pot.

Plant Safety

Topflor has been found to have acceptable plant tolerance in research trials for those crops tested and listed within this guide. However, due to the large number of species, varieties and cultivars and variable growing conditions, it is impossible to test every plant and variety or cultivar for tolerance to Topflor. SePRO has not determined whether Topflor can be used safely on all ornamental plants.

Establish specific application rates based on small-scale treatments under actual use conditions. Determine and keep records as to plant species and cultivar sensitivity before applying Topflor to a large number of plants.

Topflor Application Methods

Plants absorb Topflor through foliage, stems, and roots. Topflor may be applied as a spray, drench or chemigation to achieve the desired plant height control. Use industry standard application equipment, which may include backpack sprayers, low-pressure hand wand drench applicators, or other similar equipment. Additionally, standard chemigation equipment and practices may also be used. Multiple or split applications may allow greater treatment flexibility, more uniform growth regulation, and safety from over-application and may be, therefore, desirable.

How to Mix Topflor

The sprayer must be clean and not contaminated with other chemicals. Use the Dilution Table on the Topflor label (Table 1) to determine the amount of Topflor and water needed for the required concentration. Fill the spray tank with half the required amount of water. Measure the desired Topflor volume accurately and add it to the tank. Fill tank with the remaining amount of required water. Agitate the Topflor and water mixture frequently to assure uniform distribution during application.


Topflor applied as a foliar spray is absorbed through plant foliage and stems. Additional growth regulation will result from root uptake of Topflor reaching the root medium as runoff from foliar treatments or over-spray.

Refer to the Dilution Table on the Topflor label to determine the proper dilution instructions to attain desired Topflor concentration.

When applying as a spray, the following should be noted:

  • Do not use additional wetting agents in combination with Topflor as crop injury may occur.
  • The spray technique used should provide consistent and uniform coverage over all treated plants. Uneven application or over-application may result in irregular or excessive growth control.
  • Adequate spray volume should be used to thoroughly wet the plant foliage. The spray volume that drips down to the stem or media may be desirable as it will be taken up by the both the stems and roots increasing the effectiveness of Topflor. However, too much runoff into the media may result in excessive height control.
  • Apply uniformly at a rate of 1 gallon of spray per 200 sq. ft. of growing area, regardless of plant spacing. For small plants in small containers or plug trays that are closely spaced, use 0.5-1 gallon of spray per 200 sq. ft. of growing area. For larger plants with a well-developed canopy, a spray volume of 1.5 gallons per 200 sq. ft. of growing area is recommended.
  • Typical foliar application rate is 0.5 ppm to 80 ppm (varies by cultivar), with a maximum of 200 ppm, applied in 1 gallon of spray mix over 200 square feet.
  • Do not allow spray drift to contact non-target plants.


Topflor applied as a drench provides treatment accuracy for consistently uniform results. Topflor is readily absorbed by the roots and translocated to the terminals. Root medium should be moist, but not wet at the time of treatment. Best results are obtained when moisture content allows the drench treatment to become well distributed and retained entirely within the pot. This may be achieved by watering the plants the day before treating. Response may be variable if part of the drench solution is lost to flow-through or if root medium is too dry to allow for even distribution of the treatment, especially when multiple cuttings are in the same container. Generally, a volume of 2 fl. oz. (59 ml) is required to treat a 4-inch pot or 4 fl. oz. (118 ml) for treatment of a 6-inch pot. Typical application rate is 1 gallon of drench solution per 32 six inch potted plants. Refer to the Drench Volume Application Guidelines in the Topflor label (Table 2). Dilute Topflor to the required concentration using the method described in the Dilution Table. When applying as a drench, the use of pine bark in root media may reduce the effectiveness of drench treatments.

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