A handbbok on Weed Control in Rice.pdf

Economics of control
The economic benefit of weed control
must exceed the cost. The primary
aim of a rational farmer is to optimize
profits. One way to achieve that is to
reduce weed control costs. It is
logical, therefore, that where one or a
combination of methods exists, and
both are equally effective, the farmer
will choose the least costly.
Weed control costs include direct
costs (labor, herbicides, sprayers, etc.)
and hidden costs. Management time
wasted during frequent visits to the
field to take weed inventories to use
in weed control planning is a hidden
cost. A farmer who cleans weed seeds
from contaminated rice seeds before
planting will incur hidden costs but
will avoid future additional weed
control costs.
Selecting the weed control
methods to combine in an integrated
system will depend on the effective-
ness and cost of each method. In
some situations, hand weeding is
more expensive than applying
herbicides; in other situations, hand
weeding costs less than herbicide
application. Sometimes a combina-
tion of herbicides, or herbicides
supplemented by hand weeding, is
more economical than hand weeding
or use of herbicide alone (Tables 3.1
and 3.2).
Integrated weed
management
The resilience of weed populations
under intensive herbicide use,
buildup of weed species tolerant of
the control methods used, and
increasing public concern about
indiscriminate pesticide use and its
effects on the environment and
human health have led to widespread
appreciation of the integrated weed
management concept (Fryer and
Matsunaka 1977, Fryer 1983).
46 Weed control handbook
Table 3.1. Economic acceptability a of direct weed control methods in irrigated transplanted rice
in the Philippines (data for analysis obtained from Moody et al 1983).
Control method
No weeding
One hand weeding
Two hand weedings
Two rotary weedings
2,4-D (0.8 kg/ha)
Thiobencarb/2,4-D
(1.0 + 0.5 kg/ha)
Grain
yield
(t/ha)
1.5
3.6
3.7
2.9
3.1
3.3
Total
variable
cost (US$)
0
50
90
44
10.3
19.0
Total Return above Marginal
return variable cost benefit-
(US$) (US$) cost ratio
263 263
630 580 6.3
648 558
3.3
508 463
4.5
543
532 26
578 559 16.0
a Assumptions: Labor = US$2.09/d; First hand weeding = 24 d/ha: Second hand weeding = 19 d/ha: First rotary
weeding = 11 d/ha; Second rotary weeding = 10 d/ha: Herbicide = 2,4-D (0.8 kg/ha) = US$10.30. Thiobencarb/
2,4-D = US$19.
Table 3.2. Economic acceptability a of direct weed control methods in broadcast seeded flooded
rice (De Datta and Ampong-Nyarko 1988).
(US$)
Rate Weed Grain Marginal
Control method (kg ai/ha) biomass yield Total Total Return benefit-
(g/m 2 ) (t/ha) variable return above cost
cost variable ratio
cost
No weeding 287
Butachlor 1.0 238
Butachlor + 1 0.5 21
hand weeding
2.1 0
2.7 18.4
4.2 110
350 350
473 455
735 625
a
Assumptions: Labor = US$2.09/d, One hand weeding = 48 d/ha. Herbicide = butachlor (1.0 kg ai/ha) =
US$18.40.
Integrated weed management is
the rational use of direct and indirect
control methods to provide cost-
effective weed control. A further
refinement, implied in the terms
integrated weed management and
integrated pest management (IPM), is
that, whenever possible, weed control
should be integrated with measures
that further protect crops from
insects, diseases, nematodes, and
other injurious organisms, and
should be practiced with an under-
standing of the interrelationships
between weed populations and those
organisms. An illustrated guide to
integrated pest management (Reissig
et al 1985) is available from IRRI.
–
5.7
2.5
Several cultural methods have
been suggested to complement direct
methods in an integrated approach.
However, researchers often do not
provide an economic assessment of
these indirect methods. As a result,
farmers and their agents frequently
misjudge the economic significance of
the new methods whose adoption
they are considering. Among the
commonly suggested indirect meth-
ods for rice are land preparation,
water management, plant spacing,
seed rate, cultivar use, and fertilizer
application. Direct methods include
hand weeding and use of herbicides.