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 58
AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
roller that is continuously moistened by herbi-
granular herbicides. They are generally refined
cide solution. The roller may be a foot or more
fertilizer applicators or seeders, and some simul-
in diameter.
taneously plant seeds, distribute fertilizers, and
j. Controlling Drift. No discussion of spray
apply herbicides. Some include incorporation
application would be complete without mention-
equipment. The major components are a band
ing drift problems. Drift can result in consider-
distributor or spatter plate that distributes the
able damage to susceptible plants outside the
granules laterally and uniformly over the desired
treatment area, and can lead to costly litigation.
bandwidth, and an easily calibrated device that
(1) Drift is a function of droplet size and
meters the granules.
atmospheric conditions. Droplets 10 micrometers
a. Meters and Nozzles:
in diameter can drift up to 1 mile when released
(1) Metering devices have reached a high
at a height of 10 feet in a 3 mi/h wind. The
level of precision, and several different types are
small the droplets, the more likely they are to be
used. Among these are a variable orifice with a
carried by air movement. Larger drops drift less,
rotor-bar agitator between the hopper and the
but they do not provide as uniform plant
orifice, a variable orifice with a rubber-flanged
coverage.
impeller, a variable orifice between the hopper
(2) Research indicates that droplet size is
and an oscillation plate, and a fixed orifice with
affected by operating pressure; nozzle design;
a variable-speed screw-conveyor auger.
nozzle orientation; properties of the spray liq-
(2) Five types of nozzles or distributors are
uid; and atmospheric conditions.
available for spreading granules. Distribution
(3) Few nozzles used for spraying will pro-
patterns in the field are usually more uneven
duce uniform droplets large enough to minimize
than laboratory patterns, because some granules
drift, yet small enough to provide even coverage.
move laterally after hitting the ground. A chain
A spray nozzle designed to produce a mean
drag may reduce the lateral movement of gran-
droplet diameter of 150 micrometers also pro-
ules by roughening that convex surface left by
duces many tiny droplets ranging from 1 to 2
press wheels. Studies have shown that down-the-
micrometers and coarser droplets ranging from
row distribution is more uniform than across-
300 to 400 micrometers. Efforts have been made
the-row distribution.
to formulate sprays so that the drops produced
(3) Wind speeds of 10 mi/h or more may
by a particular type of nozzle will be large
cause considerable shifting of the distribution
enough to reduce drift. These efforts have been
pattern. Special wind guards have been devel-
only partly successful, because small drops com-
oped to prevent lateral movement of the gran-
monly form from fluid pulled from the surface
ules under windy conditions.
of the larger droplets. Also, evaporation of
b. Soil Incorporation Equipment:
spray droplets decreases their size as they fall.
(1) Granular herbicides are often mechani-
(4) The spray operator can use various
cally incorporated into the soil to reduce their
measures to control droplet size. Water-soluble
loss and to bring them into contact with germi-
thickening agents are often added to spray
nating weed seedlings. Incorporation is needed if
liquids to increase average droplet size. A water-
thiocarbamates or other volatile herbicides are
imbibing polymer is sometimes used to create
applied. The incorporation method varies with
particulated gel spray. The smallest droplet of
the chemical and physical nature of the herbi-
such a spray is predetermined by the size of the
cide, the soil conditions and properties, the
polymer particle. The use of an invert-emulsion
method of water application, and the crops and
spray (water droplets suspended in a continuous
weeds involved.
oil phase) that has high viscosity will reduce
drift. Decreasing the delivery pressure in spray
(2) Attempts have been made to incorporate
systems will produce large droplets, and rela-
herbicides with almost every implement used to
tively high-volume "dribble bars" have been
till the soil. Under proper conditions, desired
designed that operate under minimum pressure.
results can be obtained with harrows, disks,
Also, a vibrating nozzle designed to provide
subsurface blades, bed shapers, and power-
uniform droplet distribution from low-pressure
driven rotary-tillers.
streams offers promise for relatively drift-free
(3) With overhead irrigation, shall incorpo-
applications.
ration with a harrow or rotary-tiller may suffice
to prevent the loss of volatile herbicides until
water carries them deeper into the soil. With
8-3. Granule Application Equipment. A wide
furrow irrigation, deeper and more thorough
variety of applicators are used to broadcast
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