Environmental Engineering Reference
In-Depth Information
tions and mixtures of these compounds are available, but they are readily
available in most countries. All of them are relatively harmless to turf-
grasses when applied according to label recommendation, but all can
damage trees, shrubs and flowers. Trees and shrubs are particularly
sensitive to dicamba because this herbicide is mobile in the soil and can
easily be taken up by roots.
The most effective control of broad-leaf weeds is obtained when post-
emergence herbicides are applied as sprays to foliage. They must be
applied when rain is not expected. Most current formulations require
several hours for adequate foliar absorption, and if rain comes earlier,
control may be poor. Once broad-leaf weeds are eradicated, properly
conducted cultural practices, especially frequent mowing and adequate
fertilization, can prevent their re-establishment for many years.
Chemical control of grass and grasslike weeds
The most troublesome grassy weeds in the tropics are crab-grass (
Digi-
taria
spp.), goose-grass (
Eleusine indica
) and nutsedge (
Cyperus
spp.).
Digitaria
is relatively easy to control in cynodon turf, especially when
mowing height exceeds 10 mm. A chemical called methanearsonate
(MSMA), a member of the herbicide family called organic arsenicals, is
especially effective against
Digitaria
spp. Application of MSMA at the
label-recommended rate usually produces excellent control and only
minor, short-duration discoloration of cynodon turf. Goose-grass can be
effectively controlled with a combination of more than one organic
arsenical. Particularly effective is MSMA mixed with metribuzin, but
the full label-recommended rate can be safely applied only on cynodon
turf. Zoysia-grass turf is more sensitive to organic arsenicals, but when
they are applied at reduced rates, control of
Digitaria
and
Eleusine
by
MSMA can be moderately successful and zoysia injury only modest.
Other species, such as paspalum, centipede grass, Bahia grass and St
Augustine grass may be severely injured by organic arsenicals, so
MSMA should be strictly reserved for cynodon and possibly zoysia
grass, if modest discoloration of zoysia turf can be tolerated.
Fenoxaprop-ethyl, a member of the aryl-oxy-phenoxy herbicide fam-
ily, produces good control of grassy weeds, especially
Digitaria
spp. in
zoysia-grass turf. Cynodon and other turf-grasses do not tolerate this
chemical and sustain severe injury, whereas zoysia grass shows only
minor discoloration.
Sethoxydim is another aryl-oxy-phenoxy herbicide and the only one
that provides excellent control of grassy weeds in centipede grass turf,
but it cannot be used on any other turf-grass.
Paspalum, St Augustine grass and Bahia grass tolerate post-
emergence herbicides poorly, and grassy weeds cannot be safely
controlled in these species by chemical means.
