AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
PLANT GROWTH REGULATORS (PGR)
Section A -- General Information
forestall any significant reduction in mowing
frequency. Also, continuous use of PGRs over
5-1. Uses of PGRs. PGRs are applied to turf
several years may cause a shift from desirable
grass to retard or inhibit the grass' vertical shoot
turf grass species to other grasses and broadleaf
growth. They have potential to reduce mowing
weeds. Such a species shift can decrease the
costs. They can have other uses, including:
visual quality and utility of a stand, and could
(1) controlling grass growth during wet periods
affect the foraging habits of birds and other
in the spring, when frequent mowing is neces-
sary but difficult to accomplish; (2) reducing the
frequency of mowing where visual quality is not
5-3. Areas Where PGRs May Be Useful. There
important; (3) reducing the need for mowing on
are many areas on military bases where PGRs
steep slopes, along drainage ditches, roads and
might be used to advantage:
runways, and in other areas where mowing is
a. Along runways and taxiways.
difficult or dangerous.
b. In antenna fields.
c. Around taxiway and runway lights, runway
5-2. Limitations of PGRs. PGRs sometimes
distance markers, fences, guardrails, telephone
poles, power lines, guy wires, and buildings.
have harmful effects on turf, and in some
d. On ammunition, weapon, and fuel storage
locations they are not consistently effective.
a. PGRs frequently discolor or kill grass tis-
e. In and around drainage ditches.
sues, increase the susceptibility of turf to dis-
f. In fenced-in areas such as electric trans-
ease, stimulate higher than normal growth rates
formers and radar antenna sites.
after their regulatory effects have dissipated,
g. In rights-of-way.
reduce the recuperative capacity of turf, and
h. On golf course roughs, driving ranges, and
decrease turf density. Reduced recuperative ca-
difficult to mow areas, such as adjacent to sand
pacity occurs because little, if any, leaf, root,
tiller, rhizome, or stolon development occurs in
i. In cemeteries.
turf during the 6 to 8 week period after a
growth regulator is applied. This effect precludes
using PGRs on heavily trafficked turf areas,
5-4. Available PGRs:
a. The PGRs currently labeled for use on turf
such as parade grounds and athletic fields where
the turf's recuperative potential must be high.
grasses are amidochlor, chlorflurenol, maleic
The thinning of turf grasses by PGRs, and the
hydrazide, and mefluidide. Each has limitations
on application rates and the species to which it
stress, insects, and disease that may follow their
use, lead to weed encroachment. Because of
may be applied. These limitations are listed on
these disadvantages, PGRs are normally recom-
the label. Information on these PGRs and their
use is in attachments 4 and 21.
mended for use in low-maintenance and
b. Two other PGRs may be registered in the
b. Using PGRs on grass species not on the
label, or under unusual or stressful (i.e., hot and
(1) American Cyanamid Company (Prince-
dry) environmental conditions, has serious risks.
ton NJ 08540) will market imazethapyr plus
Most research with PGRs has been conducted on
imazapyr (trade name is Event) in 1989. Event
effectively suppresses foliar growth of tall fes-
fescues, Kentucky bluegrass, perennial ryegrass,
bermudagrass, bahiagrass, and centipedegrass in
cue, perennial ryegrass, Kentucky bluegrass, and
bahiagrass. It also controls seedhead production
cool and moist environments, or transitional
zone climates, not in tropical or arid regions.
of tall fescue and perennial ryegrass, and sup-
presses seedhead production in Kentucky blue-
Also, there is little information on their effects
on nonturf grass species or on weed grasses.
grass for 60 to 90 days.
c. Applying PGRs to mixed stands may sup-
(2) Elanco Products Co. (Indianapolis IN
46285) is expected to register flurprimidol (trade-
press the growth of some, but not all, species or
cultivars in the stand. Failure to suppress the
name is Cutless) in 1989. Flurprimidol effec-
tively suppresses the growth of cool-season
growth of even one species in a mixed stand may