A handbbok on Weed Control in Rice.pdf

Controlled-droplet applicator
A controlled-droplet applicator (CDA)
produces uniform-sized droplets of
spray. Weeds may be effectively
controlled with as little as 18 liters
water/ha. Droplet size is controlled
within narrow limits by spinning discs
inside the applicator. Controlled-
droplet applicators are lightweight.
They have a plastic spray head, a small
motor that drives the rotating disc, a
liquid reservoir, a handle, and a power
supply (e.g., one to eight 1.5-volt dry-
cell batteries). Models that use a
manually operated air pump (Fig. 4.3)
(e.g., Birky sprayer) have been intro-
duced. This eliminates the cost of
batteries for the first-generation CDA.
Granular applicator
Herbicides sold as granules are applied
using granular applicators. Whatever
its size, a granular applicator consists
of a hopper to contain the granules, a
metering device to control flow rate,
and a distribution mechanism. Granu-
lar herbicides that are soluble in water
may not require the same uniformity of
distribution as those that are not
soluble in water.
Granules are often applied by hand,
especially in the tropics. Because
broadcasting granules by hand is not
precise, the quantity of herbicide used
will be higher than with other
application techniques. More uniform
application can be achieved on small
areas by shaking the granules from a
container with a perforated lid.
Hydraulic applicator (pressurized)
Hydraulic applicators commonly
consist of a tank, pump, and nozzle.
Other components include an agitator,
pressure gauge, pressure regulator,
hose, and boom. The tank that holds
the spray solution is made of a
56 Weed control handbook
corrosion-resistant material, such as
stainless steel, polyvinyl material, or
fiber glass. The tank has a special lid
through which it is filled. The lid
contains a strainer to remove debris
that might clog the nozzle. The pump
drives the solution through the pres-
sure chamber to the nozzle. The most
widely used small hydraulic applicator
is the lever-operated knapsack sprayer
(Fig. 4.4). For a detailed discussion, see
Pesticide application methods (Matthews
1979).
4.2 Top, a leverage-operated
knapsack sprayer; bottom, a
controlled-droplet applicator.
Operation of the
knapsack sprayer
Herbicide and water are poured into
the sprayer tank. The lever is moved
up and down, causing the pump to
draw spray liquid from the tank into a
special chamber inside the tank called
the pressure chamber. Air trapped in