Herbigation: Applying Herbicides Through
Sprinkler Systems,
By Eugene Heikes l
•
Long ago, man
recognized
the
potential of irrigation for increasing agricultural production.
But poor management and lack of
information
caused
many
early IrrIgation systems in the
United States to fail. Most of
today's irrigation techniques have
been developed since World War II,
including sprinkler irrigation and
automated systems such as center
pivots .
Herbigation - the use of irrigation systems to apply herbicides began in the late 1960' s and has rapidly gained acceptance. Much of the
early herbigation research was done
in Colorado, Nebraska, Kansas and
Wyoming . In recent years, with the'
rapid expansion of sprinkler Irrigation, this technique has spread to
other areas.
From the beginning, there were
many questions and problems, including:
-
•
-
Rates of herbicides or combinations on
different weed spectrums and soil
types.
Proper water rates.
Types of injection equipment and adaptation to sprinkler systems.
Uniformity of distribution and incorporation of herbicides with irrigation
water.
Effect of wind during application.
Effect on crops.
Mechanics of applying herbicides with
irrigation water. including agitation of
the spray solution. calibration of sprinkler systems and safety devices to prevent ground water pollution .
'
Some answers have been found
through university research and
some by innovative farmers. There
are still questions, but there is
enough information now to make
sound recommendations and be
confident about performance.
lOr. Eugene Heikes is Extension Proressor of Weed Sci·
ence. Colorado Slale University, Fort Collins, Colorado.
Ot . He\\o.ts. \'!. a na\\vt of MQntana and. ~tve<1 as. a Cout\\'j
Extension Agent and as an Extension Weed Specialist in his
home state before becoming E'lension Weed Specialisl for
the Colorado E.tension Service in 1961 . Dr. Heikes has can·
ducted many field trials and has had e.periments with herbi·
galion f(\T the past seven years. He is highly respected for his
inno\,aHve Ideas and practical approach. He has served as
President of the Western Society of Weed Science and has
been acti\'c in the Weed Science Society of America.
Advantages
In the Western states, where rainrime:; , irrigation is not needed at this
fall cannot be depended on to protime. In most areas , however, herbivide moisture for herbicide "activacick:s are applied in about a halftion," most preplant herbicides
inch of water, usually not enough to
must be mechanically incorporated ' harm the germinating crop.
Herbigarion must be planned to
into the soil. This is usually done
before the crop is planted . Herbigacoincide with otht;r farming operation eliminates this use of energy.
tions , including planting . If the
expense and time. It also reduces
planter gets more than two or three
soil compaction.
days ahead or herbigation, weed
Where minimum tillage is used,
seedlings may become established.
herbigation eliminates most of the
It is generally recommended that
"tie-up" of the herbicide by crop
herbigation be done as soo n after
residue. It also eliminates skips and
planting as possible, or, in some
overlaps common with conventional
cases, even before planting.
ground applicators~
With center pivots , if there is
When mechanical equipment is 'more than 'two or three days delay
used , incorporatiap must be done as
after planting, about half of the cirsoon after applicaifon _as possible,
'de should be planted and herbiga·
and the herbicide must be uniformly
tion started before the other half is
incorporated into the top two or
planted .
;hree inches of soil. Applying the
Another disadvantage is herbicide
herbicide through a properly caliloss in run-off water or by' deep
brated irrigation system greatly simleaching. With proper irr'igation
plifies application .
management, these losses '".::an be
Maximum use of existing equipavoided.
ment is important. For years,
farmers have applied fertilizers
through sprinkler systems. They
have the injection pumps and holding tanks, so it is a simple matter to
apply herbicides with the same
Reprintcd~ by kind
equipment.
Another advantage is that some
permission from:
herbicides can be applied over the
WEEDS TODAY
top of a crop canopy. Sprinkler irri309 W. Clark Street
gation will carry the herbicide down
Champaign~ IL 61820/USA
through the crop foliage to deposit
it in the soil, reducing the "umbrella
effect. " This is especially important '
Reprinted and distributed
for control of late season weeds'
such as sandburs in corn and barnby :
yardgrass in potatoes.
Limitations
As with any new technique, there
are limitations. Most of these can be
overcome and, are outscored by the ·
advantages. .
Most preplaot or preemergence
herbicides should be applied before
weed seeds ~ germinate or before
weeds emetge, so hertlicides should '
be applied ·through .irrigation sys~
terns SOOl)., after planting. Some-'
International Plant
Protection Center
Oregon State University
Corvallis~ OR 9?331/USA
Loss by run-off can be minimized
with catchment basins, and the water returned to the field. Deep leaching can be avoided by adjusting the
water applied to the soil type. Since
various herbicides leach at different
rates, this should be considered
when selecting the herbicide for use
in irrigation water on a particular
soil type. If possible, it is best to
apply herbicides to a dry soil, especially highly volatile herbicides.
back pressure of the water in the irrigation system has minimum effect
on the output. The herbicide is in. jecte~ into the system between the
well al1d the pivot.
There is some risk of ground water pollution if adequate safety deviceS are not installed on the pumping equiptnt!ffi . .Check valves should
t
be instalied to prevent water from
running back into the well. Also, the
pump should be equipped with interlocking systems so the injection
pump stops when the irrigation
pump stops, or vice-versa. For internal combustion engines. the ipjection pump is usually Qelted to the
drive shaft or accessory pully of the
Spring winds may also affect distribution. Winds more than 15 mph
will cause excessive distortion of the
spray pattern. This may blow the
herbicide onto adjacent fields.
Procedures
In Colorado, most herbigation is
done with center pivot sprinklers,
with water pumped from underground aquifers. Injection of the
herbicide into a sprinkler system is
normally done with an electric or
belt-driven pUHlp. Injection pumps
are positive displacement, so the
)
Electric driven injection pump, control panel, and holding tank commonly used to
apply j1erbicides as well as fertilizer through the center pivot irrigation system.
Center pivot sprinkler system applies preemergence herbicide immediately after
planting for effective and economical weed control. This Gifford·HiII system is widely
used in the Midwest.
r·ngine; thus l he two pumps automatically stop together ,
With electric driven lrngation
pumps, a separate eledric motor is
needed to power the injection_
pump; the controls for the two motors should be interlocked so both
motors will stop when the motor on
. 'the irrigafion pump stops, or if the
motor on the injection pump stops.
There should also be a switch to
shut off the systems if the injection
pump loses its prime or stops injecting fot some reason. Without this,
all purrips may be operating without
... herbicide being injected.
In the past, most injection pumps
used for h_erbi~atjon were the same
ones used to inject fertilizers. These
were designed to handle relatively
operating condition, will perform at
least as well as when applied with
conventional ground equipment.
This has been true for most corn
herbicides tested in Colorado as well
as in Nebraska and Kansas . Work
on potatoes has been done in Idaho
and Washington and in California
on sugarbeets, alfalfa and several
vegetable crops.
Gated Pipe System
Most experiments in Colorado
have been with center pivot sprinkler systems, but work has also been
done with injection into gated pipe
systems. The purpose was to evaluate control of late season weeds in
the water furrows . Herbicides were
injected into the water, much the
same as with center pivot systems.
Water without herbicide was later
run through the furrows.
With this method, results were acceptable but not as good as with
center pivot application. This
method does, however , have potential.
Summary
Weed control when the herbicide is applied through the irrigation system is excel·
lent. Photo at top shows check area where sandbur is competing seriously with the
corn. Lower picture shows a weed· free corn field treated with Eradicane.
Application of herbicides through
irrigation systems appears to have a
bright future. However, farmers
should proceed with caution. As
with any new practice, each farmer
should become familiar with the
practice and know how it will perform with his conditions. The future
of herbigation will depend largely
on development of equipment that
is accurate and simple to use.
large volumes, so when herbicides
were used, water had to be added to
increase volume.
Recently, several manufacturers
have developed low volume injection pumps, making it possible to
inject either the concentrated herbicide formulation or low volume
mixtures . This has eliminated some
of the problem of constant · and
thorough agitation of the herbicide
solution in the holding tank. It has
also made calibration easier.
Performance
Research and field experience indicates that preplant and preemergence herbicides applied with
properly adjusted injection pumps
and ce'1ter pivot sprinklers in good
Surface irrigation system incorporates a new automatic control valve that regulates
water flow precisely to need. This system is also used to apply herbicides to the soil.