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 33
AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
Regulators can, and generally should be, tank-
Reapplication may be needed in late spring or
mixed with herbicides to control broadleaf
early summer, if season-long inhibition is desired
weeds. When applying a PGR to cool-season
and if soil moisture is abundant. High visibility
grass containing broadleaf weeds, the PGR
areas may require periodic mowing throughout
should be tank-mixed with 2,4-D in combination
the spring and summer to maintain a uniform
with at least one of the following: mecoprop
appearance. Turf should not be allowed to
(MCPP), dicamba (do not use dicamba adjacent
develop severe drought stress, and the encroach-
to, or under the drip line of, trees, shrubs, and
ment of weeds, insects, and diseases should be
ornamentals), dichlorprop, or trirlopyr (attach-
monitored.
ment 11). Tank-mixing two or three broadleaf
b. PGRs appear to offer the most benefit
herbicides with a PGR increases the spectrum of
when applied to cool-season grasses in early
herbicidal activity against various weed species,
spring. An early application will greatly reduce
Read the labels of all the chemicals before tank
the "spring flush" growth of Kentucky blue-
mixing to guard against possible incompatibili-
grass, tall fescues, and other cool-season turf
ties and other hazards.
grasses. This may be particularly useful in the
d. Avoid drought stress, if possible, and mon-
spring when frequent rainstorms can create diffi-
itor disease and insect activity in treated turf.
cult mowing conditions, especially on steep
slopes, and when part-time labor for mowing
e. It may be necessary to overseed when
environmental stresses and pests have badly
may not be available.
injured PGR-treated stands. Cool-season turf
c. In general, PGRs should be applied to
grass species should be overseeded in the autumn
cool-season turf grasses only once annually in
with equipment that will ensure proper seed
areas where heat and drought stress begin by
contact with the soil.
late spring. The single PGR application will
f. Periodic mowing will be needed to maintain
inhibit the vigorous spring growth of the cool-
uniformity and improve turf appearance in
season grasses, and environmental stress will
highly visible areas such as roadsides. Periodic
inhibit the summer growth. A second application
mowing becomes increasingly important where
during the period of stress may be severely
the stand contains a mixture of different species.
phytotoxic. Fall application to cool-season
As previously noted, not all grasses in a mixed
grasses should be considered only for dense,
stand will be similarly retarded. Orchardgrass,
vigorously growing stands.
velvetgrass, tall oatgrass, and Trisetums are less
d. The warm-season grasses, unlike cool-
affected than most other grasses. Small spots of
season grasses, grow most vigorously during
PGR-resistant grasses can be trimmed with
periods of high temperature in the summer.
hand-held mowers.
They generally are low-growing species such as
g. Turf grass areas treated with PGRs should
bahiagrass, bermudagrass, carpetgrass, St. Au-
not be subjected to more than occasional traffic
gustinegrass, and zoysiagrass, that are main-
of people, animals, and vehicles. PGR-treated
tained at low mowing heights in order to ensure
turf has a reduced capacity to recuperate from
vigorous, dense stands, and to reduce the poten-
injury while the inhibitory effects of the chemi-
tial for winterkill.
cal persist.
e. Warm-season grasses are normally treated
h. There may be situations when growth inhi-
to suppress seedheads rather than foliar growth.
bition by PGRs must be reversed. An applica-
It is difficult to obtain season-long seedhead
tion of 40 to 50 lb/a of actual nitrogen in a
control with a single PGR application because
water-soluble fertilizer will enhance growth and
many warm-season grasses produce seedheads
partially reverse growth inhibition. For these
continuously throughout the summer. Warm-
fertilizers to be effective, they must be watered-
season grasses also generally require higher ap-
in by irrigation or by a timely rainfall.
plication rates of PGRs than do the cool-season
grasses.
f. Where warm-season grasses become dor-
5-7. Applying PGRs:
mant in winter, treatment should begin after
a. PGRs should be applied no later in the
spring greenup. In regions where warm-season
spring than 2 weeks before seedheads normally
grasses grow year-round, PGRs have had erratic
appear, Turf to be treated should be mowed 24
effects, and therefore, they are generally not
to 48 hours before application, and it should be
used on warm-season grasses in subtropical and
mowed again 2 to 3 weeks after application.
tropical climates.
Growth retardation lasts about 6 to 8 weeks.
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