Mastiff Flurprimidol


Mastiff PGR is a plant growth regulator (PGR) which produces desirable growth reduction in a wide variety of ornamental trees. With a single Mastiff PGR application, vegetative growth generally is reduced up to 70% over a three-year period. Results will vary depending upon tree species and local growing conditions. For use by professional arborists/applicators, grounds maintenance professionals, city foresters, electric utility foresters/contractors, and landscapers.

Mastiff is ideal for trees

  • Planted too close together
  • Too close to homes, decks
  • Along scenic lines of sight
  • Near utility and power lines
  • Along sidewalks or in vaults
  • Placed in containers or tree wells

Boost Tree Health

Mastiff condenses shoot elongation and stimulates root development. This increases root-to-crown ratio which can increase stress resistance and speed recovery from stress brought on by drought, pollution, and
temperature extremes.

Mastiff provides beneficial tree growth
reduction and lets you:

  • Reduce growth where trees are planted
    too close together or in tightly landscaped areas.
  • Manage growth of trees planted too
    close to homes, decks, foundations,
    or other structures.
  • Maintain scenic view with less trimming.
  • Manage size and improve vitality of trees
    in vaults, along sidewalks, in parking
    lots, or in interior spaces.
  • Extend trimming cycles, reducing labor
    time and expenses.
  • Stimulate fibrous root systems.
  • Improve vitality in overly mature trees
    or those in mild decline.

Ideal for Municipal and Utility Corridor Trees

  • Under or near utility and power lines
  • Along rights-of-way
  • Near intersections or streetlights
  • Along scenic corridors
  • Where undergrowth limits signage visibility

Mastiff helps utility and ROW managers extend trimming cycles, reducing trimming in dangerous areas, and decrease vegetation-related power outage risks in utility corridors.

Mastiff helps municipal arborists maintain scenic views, control lines of sight near intersections, and keep signage visible in retail areas.


Active: Flurprimidol*
(CAS No. 56425-91-3)
Other Ingredients 51.9%
Total 100.0%

*Equivalent to 3.35 lbs. Phosphorous Acid/gallon

EPA Reg. No. 67690-34-69117
EPA Est. 69117-NE-1

Application Rate

Inject 1 ml every 4″ around the base (flare) of the tree. Dosage may be increased to 2 ml per injection site for trees with diameters over 12″. See label for details

Higher or lower dosages are recommended for selected species. See the Supplemental Species Rate Chart (48KB PDF) for details.

Timing of Mastiff Injections

Shoot growth is most common between April and June. Mastiff PGR applications made prior to shoot growth, either in early spring or the preceding fall, provide more first-year growth control than applications made at other times. Late spring, summer, or fall applications will provide growth reduction the following year. Regardless of application timing, growth reduction within the first year after treatment may not be as noticeable as in subsequent years. A single Mastiff PGR application provides tree growth regulation for approximately three years. Do not apply more than once every three years.

Additional information

Weight 2 lbs
Dimensions 4 × 4 × 8 in