Page 63 - Ilmu Tanah

50 The Chemistry and Fertility of Soils under Tropical Weeds

Chemical Weed Control

Chemical control of weeds is the method to control weeds by using lethal
chemical substances, organic or inorganic. The chemical control of weeds using
herbicides is now probably the most popular method, both in Indonesia and in the
world, together with the mechanical physical technique. The total selling of
herbicides in Indonesia for the year of 2006 reached 246.8 millions euros or about
3.5 trillion rupiahs, 43% of which was the selling of insecticides, 15% was of
fungicides, while the selling of herbicides was 40% or about 99.1 millions euros or
about 1.4 trillions rupiahs (Croplife Asia, 2007).
There are some reasons for the popular use herbicides by farmers: efficient
use of labor and time, economical (cheap control cost), plenty of available choices
and easily obtained in the market, able to control weeds difficult to control by the
mechanical-physical techniques like perennial weeds, and give a clear result with
good controlling effects. A great deal of research data show that herbicides were
able to depress weed growth for a period 12 weeks or 3 months after application,
comparable to the method of mechanical physical control (weed clearing) which
needs more time, labors, and funds. Glyphosate 620 AS and 480 AS were able to
depress weed dry-weight of oil palm, rubber, coffee, and cacao until 12 weeks after
application (WAA), meanwhile sulphonate 480 AS and 240 AS as well as paraquate
applied for no-tillage land preparation of upland rice was also able to depress the
weight of weed until 7 WAA. In paddy fields siklosuphamoron and sihalofop butil
were able to control weeds until 12 WAA (Sriyani et al., 1998; Sriyani 1999; Sriyani
et al., 2001; Sriyani et al., 2003; and Sriyani et al., 2004).
However, the use of herbicides may also give negative effects on human life
and environment. This occurs due to various reasons among which: inappropriate
handling and application, user negligence of not using approriate safety tools
during application, inaccurate dose and concentration, wrong time of application,
and inappropriate types of herbicides for particular weeds. Recently, the
continuous use of herbicides for more than 50 years globally has caused the
development of several herbicide-resistant-weed species, which makes the
management of weeds are more complicated and expensive.
The use of herbicides must fulfil five accuracies, i.e. accurate target weeds,
accurate types of herbicides, accurate dose of herbicides, accurate time of
herbicide application, and accurate method of herbicide application. Farmers must
first make an accurate identification of problem weeds. This step is very important
to accurately choose approriate herbicides for particular weeds. In fact there are
various herbicides with various different active ingredients with different

Abdul Kadir Salam and Nanik Sriyani – 2019