Environmental Engineering Reference
In-Depth Information
turf. Because these plants, like desirable turf-grasses, have growing
points close to ground level, mowing does not eliminate them effectively.
In the tropical climate, the most challenging are perennial and intrusive
grasslike species that tolerate low mowing and turf-grass species en-
croaching on areas of other turf-grass species. Quite often, cultural con-
trol methods are ineffective and chemical control is required. In some
instances even chemical weed control is insufficient, and in extreme
situations the entire turf area must be renovated or the invaded turf-
grass species must be replaced with another one.
A few terms used to describe weeds require clarification because,
although they may not apply to the majority of weeds in tropical climates,
readers may come across them while reading herbicide labels, turf
publications, weed-science topics, brochures or flyers. Weed scientists
classify weeds into three major categories: annual, biennial and peren-
nial. These terms are most relevant in temperate climates, where plant life
cycles are more closely tied to the annual cycle of warm and cold seasons.
Weeds classified as summer annuals germinate in spring when soil
temperature reaches a certain level and usually die after the first autumn
frost. Winter annuals emerge in the late summer and die the next year.
Biennials live for two years only, accumulating resources in the first year
and flowering in the second, and perennials persist for many years. Weed
scientists at research centres and numerous chemical companies have
developed weed-control programmes for their largest markets, most of
which are located in temperate climates. Recommendations are devel-
oped for specific groups of weeds persisting in these climates and usually
tell turf managers what cultural practices to employ, what herbicides to
use, and how and when to apply them to assure the best weed control. In
the tropics, however, many of these recommendations are not applicable.
Annual weeds do not exist; species considered annual in the temperate
zone persist for years, developing tougher stems. In dense turf, they
spread mainly vegetatively rather than by seeds, and when established
persist indefinitely. Weed-control data from temperate climates and
herbicide label instructions should serve as general guidelines, but sub-
stantially different results can be expected. Information on weed control
in the tropics should be drawn from publications prepared specifically
for tropical locations.
Non-chemical weed control
Healthy and vigorous turf is often free of weeds. Because weeds encroach
mainly on weak or damaged turf, proper management techniques can
stop or reverse weed infestation. Prevention is as important as cultural,
mechanical, biological and chemical means of weed control.
