Environmental Engineering Reference
In-Depth Information
Some weeds cannot be controlled by selective herbicides in particular
types of turf. Spot treatment with a non-selective herbicide such as
glyphosate is the most reliable means of removing these weeds from
the turf. Foliage-applied glyphosate is translocated to roots, stolons and
rhizomes and slowly kills the entire plant. Glyphosate should be sprayed
on actively growing weeds, and wind drift toward non-target areas
should be avoided.
Besides crab-grass and goose-grass, nutsedge (
Cyperus
spp.) seems to
be the most troublesome weed in tropical turfs. It resembles grass, but
like all sedges, it has a triangular stem with three-ranked leaves, not the
round stem with two-ranked leaves typical of grasses. The
Cyperus
root
system is fibrous and produces deep-rooted tubers or nutlets. Like all
sedges, it typically thrives in soils that remain wet for extended periods
of time. Historically, post-emergence chemical control of
Cyprus
was
attempted with repeat applications of 2,4D, the organic arsenicals or a
combination of the two, but extensive damage to most turf-grass species
was a major concern. Substantial progress in
Cyperus
control was
achieved in the mid-1990s when halosulfuron appeared on the market.
Halosulfuron belongs to the sulfonyl-urea herbicide family and provides
good post-emergence control of most sedges with only slight to moderate
discoloration of major turf species.
Starting in the 1990s, substantial amounts of research have been
conducted to develop genetically engineered turf-grasses resistant to
non-selective herbicides. Just like genetically engineered agricultural
crops, several species of turf-grasses have been modified to tolerate
otherwise lethal doses of glyphosate. When such turf is sprayed with
non-selective glyphosate, only genetically modified plants survive. This
type of weed control allows eradication of all weeds as well as acciden-
tally introduced turf-grass plants that may be of the same species but not
genetically engineered. The resulting turf is absolutely weed free and
extremely uniform. Among several genetically engineered species,
St Augustine grass is presently being tested for introduction in the near
future, and research on several other species is highly advanced.
Genetically modified turf-grasses will probably revolutionize turf-
grass weed control, making it simple and safe. As in agronomic crops,
weed control may depend upon only one chemical. Presently the bio-
technological industries are concentrating their effort on glyphosate, one
of the least environmentally harmful herbicides ever discovered.
Diseases
Fungi, and sometimes nematodes, bacteria, viruses or adverse environ-
mental conditions cause most turf-grass diseases. Literally hundreds of
