A handbbok on Weed Control in Rice.pdf

The decision to spray should be
made after considering
the degree of weed species and
weed growth,
the recommendation for weed
control,
the control measures available,
the correct timing of herbicide application,
the previous experience in spraying,
the probable cost-benefit of applying
the herbicide, and
safety.
Always follow the chemical
manufacturer’s instructions on safety
precautions.
A few days before spraying, ensure
that
chemical supplies on the farm are
adequate for the job at hand,
a readily accessible water supply for
filling the sprayer is available, and
the sprayer is clean and in good
working condition.
On the day of spraying, check to see
that
appropriate protective clothing is
worn,
the calibration used is correct,
weeds are in suitable condition for
treatment,
ground conditions are satisfactory,
weather conditions and forecasts are
satisfactory, and
the person to do the spraying is
healthy and fit.
Mixing
The concentrated active ingredient of a
herbicide must be mixed thoroughly
with water (the carrier). When using a
wettable powder, agitate the solution
to prevent the herbicide from settling
out. That would plug nozzles and give
non-uniform application rates. The
water used should be clean and free
from clay, mud, organic matter, and
dissolved salts.
Do not guess the amount of herbi-
cide to use. Always measure or weigh
the exact calculated amount. Fill the
sprayer tank about half-full with water.
Add the measured herbicide to the
tank, then fill the tank completely with
water. Be sure both herbicide and
water pass through the strainer in the
tank. Mix the contents of a knapsack
sprayer tank by shaking it.
Herbicide selection
Most herbicides are suitable for use
only in selected crops; they would kill
other crops. To assure the safety of the
rice crop, use only herbicides recom-
mended for rice. Some herbicide
groups tend to control certain families
of weeds better than others. Consider
the weeds on your farm and select the
herbicide that will control those weeds.
Nozzles
Select the most suitable nozzle size and
type. In general, use
a cone nozzle for applications where
it is important to cover the crop
foliage (e.g., for foliar herbicides),
and
a low-pressure fan nozzle for
residual herbicides.
Spraying
Do not spray when the wind is too
strong. If you must spray when it is
windy, hold the nozzle close to the
ground to prevent the droplets from
being blown away during calibration
of the sprayer and during actual field
spraying. Always walk downwind, so
that any spray blown off the crop is
carried away from you.
Always carry a spare nozzle. Check
the sprayer nozzle often for possible
blockage (this would be indicated by a
poor spray pattern) and clean it when
necessary. A faulty nozzle delivers the
wrong dosage. If a faulty nozzle
develops, attend to it at the end of the
field. Use a soft material to clean
blocked nozzles. Never clean a nozzle
with a wire or pin.
Maintain a constant nozzle height
above the target weeds in the field. A
nozzle height of about 50 cm from the
target to the ground is ideal.
Avoid missing strips or overlapping
spray swaths.
Use rice rows as a measure (spacing
from 25 to 30 cm). Walk over every
third or fourth row to give a 1-m
spray width.
Place sticks or sighting poles at
swath width intervals before
starting to spray.
While spraying, maintain a constant
walking speed. When you slow your
pace, the amount of herbicide applied
increases. When you walk faster, the
amount decreases. Underapplication
results in unsatisfactory weed control;
applying more than the recommended
amount may result in injury or death to
the rice crop. Overapplication also
wastes a costly input.
Cleaning the sprayer
Do not leave herbicide solutions in the
sprayer overnight. Whether spraying
research plots or large areas, it is
important to thoroughly clean the
sprayer before using a different herbi-
cide. Herbicides retained in the pump,
hose, boom, or sprayer tank, if sprayed
later on sensitive plants, will cause
crop injury. To clean the sprayer,
1. Rinse the sprayer with clean water
to remove most of the chemical. A
household detergent can be added to
water used for cleaning. Pour this out
and add clean water again.
2. Operate the pump for at least 10
strokes and pour out the remaining
water.
3. Repeat these procedures two more
times.
Herbicide use 61