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 AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
25
b. Water must not be applied faster than it
If a preemergence herbicide is applied immedi-
can be absorbed by the soil. Avoid frequent,
ately after verticutting or dethatching, the re-
light watering. This is wasteful, causes shallow
growth of the grass may be suppressed.
growth of grass roots, and stimulates germina-
tion and growth of weeds. For example, light,
4-7. Using Selective Herbicides. Herbicides are
frequent watering encourages the invasion of
available for most of the weeds found in lawns
annual bluegrass and crabgrass.
and other turf areas, but they should be used
only when necessary and as part of a complete
4-5. Mowing Turf. Mowing at the proper time
turf management program.
and height greatly improves weed control.
a. General Information:
a. Mow most cool-season turf grasses about
(1) Selective herbicides can be used to con-
weekly to a height of 2.5 to 3.5 inches. Closer
trol most weed species without injuring turf
mowing, especially in hot weather, weakens
grass, but they must be selected and applied with
cool-season turf and invites weed invasion.
care. An excessive dose of almost any herbicide
Crabgrass infestations, in particular, can be
will damage lawn grasses, and a herbicide may
reduced by the shading effect of a taller, denser
kill one weed but not control others. To control
stand of turf grass on the crabgrass seedlings.
some weeds it may be necessary to use herbicides
Invasion of spotted spurge, another warm-
that temporarily, or even permanently, injure
season weed, also can be reduced by high
lawn grasses.
mowing.
(2) Most lawn weeds are either grasses or
b. Mow warm-season grasses, particularly
broadleafs. Crabgrass, goosegrass, foxtail, and
bermudagrass, closer than most cool-season
barnyardgrass are examples of annual grass
grasses. Bermudagrass should be cut to a height
weeds. Dandelions, plantains, and chickweed are
of 1.5 to 2 inches. Others, such as zoysiagrass,
examples of broadleaf weeds. Nutsedge is a
centipedegrass, and carpetgrass, should be
narrow-leaf weed that is not a grass.
mowed to a height of about 1 inch. St. Augus-
(3) Each type of weed requires different
tinegrass and bahiagrass should be cut to 2.5 to
herbicides for effective control; but the herbi-
3.5 inches.
cides used for crabgrass are usually effective on
c. Mow lawns frequently, and keep the mower
most other annual grasses, and the herbicides
blades sharp. Unless growth or thatch layers are
used for dandelion, plantain, and chickweed are
excessive, and there are weeds setting seed in the
usually effective on most other broadleaf weeds.
lawn, leave the clippings on the grass. A mower
Herbicides for weed grasses in turf and for
with a mulching blade increases the rate of
broadleaf weeds in turf are shown in attach-
decomposition of the clippings. Do not let grass
ments 10 and 11, respectively. The effectiveness
grow unusually high. No more than 1/3 the
of the herbicides varies, as shown in attachment
length of the grass leaf should be removed at a
12.
clipping. If a lawn is to be mowed to 2 inches,
(4) The herbicides chosen should be both
then mow the grass before it exceeds 3 inches in
effective for the weeds present and safe for turf
height.
and ornamental plants. Attachment 13 shows the
soil persistence and potential hazards of herbi-
cides to trees, shrubs, turf grass, and herbaceous
4-6. Aerating, Verticutting, and Dethatching:
broadleaf plants.
a. In some areas, turf requires aerating, verti-
(5) The herbicides chosen must also be safe
cutting, or dethatching to improve growing con-
for people and animals using the area. Attach-
ditions. These operations should be performed
ment 4 shows toxicities of herbicides. When used
when the turf will regenerate quickly. Further-
according to label directions, the recommended
more, these operations should not uncover the
herbicides will not damage plants and will pose
soil or leave it bare at the time of year when
little hazard to the user, other persons, pets, and
seeds of crabgrass, annual bluegrass, or goose-
wildlife in the area. Always read and follow the
grass germinate. These weeds rapidly invade
directions and precautions on the label.
open areas. Early fall is the best time to
renovate cool-season turfs. Early summer is the
b. Applying Herbicides:
best time to renovate warm-season grasses.
(1) There are three types of herbicide
b. These management operations should not
application: (1) Preplanting -- application before
be performed following preemergence herbicide
seeding or sodding turf, (2) Preemergence -- ap-
applications, or the weeds will not be controlled.
plication before weed seeds germinate, and
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