Chemical Weed Control in Peanut Fields
EARL G. RODGERS, EVERT O. BURT and AUBREY C. MIXON
fT AGRICULTURAI~rErqSioN SERVICE
4 CAI~yq. 'LfoIDA
Cover Picture.-Weeds were controlled in this peanut field by a broadcast
application of a pre-emergence weed control chemical and plowing the
middles one time.
Chemical Weed Control in Peanut Fields
EARL G. RODGERS, EVERT O. BURT,
and AUBREY C. MIXON 1
Weed control is one of the major costs in peanut production.
Weeds compete with the peanut plants for water, light and
nutrients and increase the cost of labor and equipment required
for production and harvest. Severe reductions in seed quality
and total yield often are caused by weeds.
The principles of weed control in peanut fields by mechanical
methods and cropping practices are well known and have been
used for many years. No good substitutes are known for such
cultural and control measures as good seedbed preparation,
proper fertilization, the use of high quality, clean seed of adapted
varieties, proper rates, dates and methods of planting, and clean,
shallow, and timely cultivation. Such practices provide ideal
growing conditions for peanuts to crowd out many weeds.
The control of weeds in peanuts with chemicals or herbicides
is a relatively new practice that has not been used extensively
in Florida. Recent experimentation with several chemicals to
control weed growth in peanuts has resulted in the selection of
one material that may considerably reduce the cost of weed
Chemical weed control must begin with seedbed preparation
and each operation thereafter must be properly performed to
achieve best results. The land should be prepared sufficiently
early to allow good decomposition of previous crop residue be-
fore planting peanuts.
Why Use Chemical Weed Control in Peanut Fields?
A survey conducted by the Florida Agricultural Experiment
Station 2 estimates that about 12 man hours are required to con-
trol weeds in an acre of peanuts by hoeing. This is about 32%
SAssociate Professor of Agronomy, College of Agriculture; Assistant
Agronomist, Florida Agricultural Experiment Station; and Assistant
Agronomist, Florida Agricultural Extension Service of the University of
Florida, Gainesville, Florida.
Brunk, Max E. and J. Wayne Reitz, Labor and Material Requirements
for Crops and Livestock, Fla. Agric. Expt. Sta., Bul. 388, June 1943.
of the total man hours necessary to produce an acre of mature
peanuts. If farm labor is valued at 50 cents per hour, hoeing
costs about $6.00 an acre. For approximately the same amount
of money per acre, a weed control chemical can be purchased
that will control most annual weeds commonly found in peanut
fields. This herbicide eliminates the necessity of hoeing by
greatly reducing the emergence of weeds in the row.
Most common annual weeds as sand bur, crabgrass, and Mexi-
can clover (Florida pusley) are controlled for six to 12 weeks
after planting before the chemical begins to lose its effect and
weeds appear. The peanut plants then are large enough, how-
ever, to crowd out most of these weeds, since the peanut seedlings
will not have been harmed or stunted in any way.
Besides elimination of hoeing, the use of herbicide may allow
omission of early peanut cultivation and thereby make possible
during this critical time cultivation of other crops not treated
for weed control. The use of chemical weed control may be
particularly valuable in excessively wet seasons when the soil
contains too much moisture for early cultivation.
What Herbicide to Use?
The recommended herbicide is called dinitro 3 and is sold under
the trade names of Premerge and Sinox PE. It is a yellowish
brown liquid which contains three pounds of the active ingre-
dient per gallon. Other herbicides have provided favorable weed
control and may be recommended at a later date.
What Weeds Will the Dinitros Control?
Dinitro controls most annual weeds, particularly sand bur,
crabgrass, and Mexican clover (Florida pusley). Perennials such
as nut grass, Bermuda grass, and Johnson grass are not af-
When Should the Herbicide Be Applied?
Pre-Emergence Treatment.-If the herbicide is applied at
planting time or before the young peanut plants emerge from the
soil, such an application is referred to as a pre-emergence treat-
ment. The most economical application of the pre-emergence
treatment is obtained by mounting the sprayer on a tractor and
applying the chemical at the time of planting. The lack of soil
3 Dinitro refers to a group of dinitro phenols of which the active in-
gredient is alkanolamine salts of dinitro-o-sec-butylphenol.
moisture at the time of application of the chemical may reduce
the effectiveness of weed control. Heavy rainfall a few days
after treatment may injure peanut seedlings.
Post-Emergence Treatments.-When the herbicide is applied
after the peanuts emerge, such an application is known as post-
emergence treatment. The application should be made when
weed seedlings are young and the peanuts are about three to
five inches in height, or within two to three weeks after emer-
gence. This treatment will result in burning the peanut leaves,
but the plants later recover. The post-emergence application is
more effective in killing broadleaf weeds than grasses.
Weed control in peanut fields does not require the use of both
pre-emergence and post-emergence treatments. For example,
when the weed control chemical is applied as a pre-emergence
treatment, a post-emergence treatment is not necessary.
How Much Dinitro Is Needed?
For pre-emergence treatment, 1 gallon (3 pounds of the active
ingredient) per acre of dinitro is sufficient when applied in 12-
to 14-inch bands centered on 36-inch rows, covering about one-
third of the total soil surface. This gallon of dinitro should
be mixed with 10 to 20 gallons of water, or the amount of water
that the sprayer requires to cover one acre. The entire soil sur-
face may be sprayed by increasing proportionately the quantity
of dinitro used. The added cost of herbicide for spraying the
middles usually is not justified, however, since weeds there may
be controlled by normal cultivation. In performing such cultiva-
tion, fenders or other protective devices should be used to pre-
vent disturbance of the treated band of soil over the row.
Post-emergence applications require only one-third as much
dinitro as the pre-emergence treatments. That is, 1/3 gallon (1
pound of the active ingredient) per acre of dinitro is sufficient
when applied in 12- to 14-inch bands centered on 36-inch rows.
This 1/3 gallon of dinitro should be mixed with 10 to 20 gallons
of water and applied to one acre.
How Is the Herbicide Applied?
A pre-emergence treatment of dinitro should be sprayed onto
the smoothed soil surface in bands about 12 inches wide over
the row. A 12-inch roller or other smoothing device should be
attached immediately behind the planter. The nozzle then is
mounted just behind the smoothing device and its height is ad-
justed to spray a band of the desired width.
A post-emergence treatment of dinitro should be sprayed
directly onto the peanuts and weeds. A smooth soil surface is
not necessary when applying post-emergence treatments.
Cost of equipment limits the use of herbicides, particularly
by farmers with small peanut acreages. To ultilize such equip-
ment more efficiently, farmers might use the sprayer for applying
the chemical on other farms on a custom basis. The herbicide
also may be applied to small acreages with a knapsack sprayer.
Calibration of Spray Equipment
A successful weed control program requires correct rates of
herbicidal application. The rate of application in the field is de-
pendent upon several factors, including speed of the tractor,
spraying pressure, and size of nozzle opening.
Fig. 1.-Shoe type applicator for applying pre-emergence weed control
Chemicals. (Photo courtesy Hendrix-Barnhill Equipment Company.)
.- 6AMM J- .
-_- "*ysge|-^l 0
Nozzle tips of suitable sizes are manufactured by several com-
panies. A uniform rate of spray from all nozzles is essential and
any nozzle tip allowing delivery of smaller or larger amounts of
spray than others on the boom should be replaced. The grower
should be guided by the recommended combinations of working
pressures and nozzle sizes for various tractor speeds.
Several methods have been developed for the field calibration of
equipment for applying herbicides. Several guides have been
published which require a minimum of computation. One pro-
cedure is outlined below for use when sprayer pump is attached
to power take-off of tractor.
1. Accurately measure off a distance of 300 feet.
2. Set throttle for tractor to travel at desired planting speed
and, with planter and sprayer attached, determine how many
seconds are required to travel the 300 feet.
3. The following table gives sample values of such required
time in the first column opposite each of which is listed the
number of seconds required for one quart of spray to come from
each nozzle with tractor engine running at planting speed.
Seconds Required to Seconds Required to
Travel 300 Feet Collect 1 Quart of Spray
80 .........................- ... ... .. .......- 70
75 ............................................ ......... .... 65
65 .......................................... ..- ........... 60
50 .............. .... .... ..-.. ... ...... ........... 45
45 ............... ...... .. ... .. .... ............. 40
Fig. 2.-Roller type applicator for applying pre-emergence weed control
chemicals. (Photo courtesy E. I. du Pont deNemours and Company.)
4. With tractor standing still and engine running at planting
speed, adjust pressure so that one quart of liquid comes from
each nozzle in the number of seconds found above to be required
for the specific speed of travel to be used.
If more than 40 pounds pressure is necessary to deliver the
required amount of spray material, nozzles with a larger open-
ing should be used. On the other hand, if less than 25 pounds
pressure is necessary to deliver the required amount of spray
material, nozzles with a smaller opening should be used.
5. Center one nozzle over each row and adjust nozzle height
so that the sprayer band will be from 12 to 14 inches wide.
6. Approximately 12 gallons of solution will be required to
spray one acre of peanuts when the sprayer is properly regu-
lated. For pre-emergence spraying, add 1 gallon of dinitro with
each 11 gallons of water in the sprayer tank. For post-emer-
gence spraying, add 1/3 gallon of dinitro for each 12 gallons of
water in the sprayer tank.
Other Advantages of Using Herbicides
Some workers have reported less blight and root rot on peanut
plants where herbicides have been used. Soil frequently pushed
into the peanut row by early cultivation to cover new weed
growth may damage the peanut plants and increase their sus-
ceptibility to disease organisms. Since a 12-inch strip in the
row is usually controlled of weed growth for several weeks, it is
necessary to cultivate only the middle of the row at first and thus
prevent such damage to peanuts while they are young.
Before using any herbicide, study all precautions on label
relative to its use.
Wash spray equipment thoroughly after using.
Spray equipment that has been used for spraying other chem-
icals should be thoroughly cleaned before using, since certain
chemical residues may cause damage to peanut plants.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and United States Department of Agriculture, Cooperating
H. G. Clayton, Director