Herbicidal compositions of acifluorfen or salts thereof and citrates

Compositions comprising acifluorfen or one of its agronomically acceptable salts and a citrate salt, in a weight amount greater than the acifluorfen, exhibit enhanced herbicidal activity, particularly against velvetleaf.

TECHNICAL FIELD 
This invention relates to methods for enhancing the herbicidal activity of 
acifluorfens and to herbicidal compositions having enhanced activity. 
BACKGROUND OF THE INVENTION 
Acifluorfen, 5-(2-chloro-4-trifluoromethyl-phenoxy)-2-nitrobenzoic acid, 
and its agronomically acceptable salts are selective diphenyl ether 
herbicides which have both pre- and post-emergence weed control. They are 
particularly useful in the post-emergence control of a wide variety of 
broadleaf weeds. However, there are some broadleaf weeds, for example, 
velvetleaf and common cocklebur, against which its herbicidal activity is 
considered inferior. Citrate salts per se have no significant herbicidal 
activity. 
Copending U.S. patent application Ser. No. 99,769 filed Dec. 3, 1979, 
abandoned, by Gerald E. Kollman, discloses the use of an aqueous 
composition containing a water soluble salt of an inorganic or organic 
acid and acifluorfen, or an agronomically acceptable salt thereof, as a 
means for obtaining improved weed control including the control of 
velvetleaf. Additionally, sodium acifluorfen has been formulated with 
sodium citrate dihydrate to enhance the stability of the herbicide. 
However, the amount of citrate added has been generally less than about 
half the weight percent of the sodium acifluorfen present, which is 
insufficient to cause any beneficial effect on the activity of the 
herbicide. 
The present invention recognizes that compositions of acifluorfen and its 
agronomically acceptable salts in combination with citrate salts have a 
particularly pronounced effect on enhancing the herbicidal activity of the 
acifluorfen and in broadening the spectrum of activity particularly 
against velvetleaf. 
DESCRIPTION OF THE INVENTION 
According to the invention, certain herbicidal compositions which comprise 
(a) acifluorfen or one of its agronomically acceptable salts and (b) a 
citrate in an amount equal to or greater than the weight amount of the 
acifluorfen, exhibit significantly greater herbicidal activity than would 
be expected from the herbicidal activity (or lack of activity) of the 
individual components of the composition. Herbicidal activity of 
acifluorfen or one of its salts against velvetleaf is particularly 
advantageously affected by this composition. Thus, the compositions of the 
invention permit a significantly greater degree of control of velvetleaf 
than what is obtained by using acifluorfen or one of its agronomically 
acceptable salts alone. The compositions are also beneficial to the 
activity of acifluorfens against other weeds, e.g., morningglory and 
cocklebur. In addition to the increased herbicidal activity, the 
compositions still retain selectivity. 
The compositions of the invention can be applied in any amount which will 
provide the required control of weeds. The particular amount is dependent 
upon many factors including, for example, the crop, weeds sought to be 
controlled and environmental conditions. Once such factors are known, one 
in the art can readily determine the amount of the composition to be 
applied and the amount of the acifluorfen and citrate it should contain. 
The composition is generally applied in a manner so that from about 0.05 
to about 13 kilograms (kg)/hectare (ha), preferable from about 0.1 to 
about 1.1 kg/ha and more preferably from 0.13 to about 0.55 kg/ha of 
acifluorfen or one of its agronomically acceptable salts is applied to the 
locus of the crop. The citrate is present in an amount which causes the 
herbicidal activity of the acifluorfen to be venefitted. Generally, the 
amount of citrate applied will be at least about 0.5 kg/ha and preferably 
will be at least 0.1 kg/ha and will not exceed about 13 kg/ha, preferably 
it will not exceed about 8 kg/ha and more preferably it will not exceed 
about 4.5 kg/ha. Most preferably, the amount of citrate applied will be 
between about 1 and about 2.2 kg/ha. The ratio of the acifluorfen to 
citrate in the composition is at least 1:1 and not greater than about 1:35 
and preferably not greater than about 1:16. 
It is preferred that an agronomically acceptable salt of acifluorfen be 
used. Such salts are disclosed in U.S. Pat. No. 4,063,929. Preferred salts 
of acifluorfen are the sodium, potassium and amine, including ammonium, 
salts. Amine salts include primary, secondary, tertiary and quaternary 
amine salts of acifluorfen. Preferred amine salts of acifluorfen include 
mono, di, tri or tetra substituted (C.sub.1 -C.sub.4) alkylamines 
including dimethyl, diethyl and triethylamines; hydroxy (C.sub.2 -C.sub.4) 
alkylamines including monoethanol and diethanolamines and, preferably, 
ammonium and ethylene oxide derivatives of fatty acids, fatty amides and 
fatty quaternaries including bis-polyoxyethylene(5) cocoamine and 
bis-polyoxyethylene(5) tallowamine salts. The more preferred salt is 
sodium acifluorfen. Citrate salts include alkali metal, alkaline earth 
metal and ammonium salts of citric acid. The preferred citrates are sodium 
citrates, potassium citrates and ammonium citrates. Ammonium citrate and 
diammonium citrate are more preferred. 
The compositions of the invention are typically formulated as concentrated 
aqueous solutions, as soluble flowable powders containing both the 
herbicide and the citrate, or as separate concentrated solutions or 
soluble formulated powders, one containing the herbicide and the other the 
salt. The formulation can then be diluted to appropriate use 
concentrations with water. The concentrated solutions and the formulated 
powders are diluted with water to give a carrier volume of generally about 
5 to about 50 gallons per acre at the desired rate of application of the 
herbicide. 
The compositions of the invention are useful as preemergence and, more 
preferably, as postemergence herbicides. Among the crops on which the 
compositions of this invention can be advantageously employed are, for 
example, cotton, soybeans, peanuts, safflower, beans, rice, peas, carrots, 
corn, wheat, sunflowers and other cereal crops. Soybeans, peanuts, 
sunflowers and rice are preferred crops. 
A composition of the invention can be applied to the growth medium or, 
preferably, to plants to be treated either by itself or, as is generally 
done, in a form which also comprises as agronomically-acceptable carrier. 
By agronomically acceptable carrier is meant any substance which can be 
used to dissolve, disperse or diffuse a herbicidal compound, e.g., 
acifluorfen and the citrate, without impairing the effectiveness of the 
herbicidal compound and which by itself has no deterimental effect on the 
soil, equipment, crops, or agronomic environment. Mixtures of the 
compositions of the invention may also be used in any of these herbicidal 
formulations. Compositions of the invention can also be mixed with or used 
in conjugation with the herbicide bentazone, 
3-isopropyl-(1H)-benzo-2,1,3-thiadiazin-4-one-2,2-dioxide. 
When it is desirable, particularly in postemergence applications, 
adjuvants, such as dispersing agents, stickers, adhesives, and the like, 
may be included in accordance with agricultural practices. Examples of 
adjuvants which are commonly used in the art can be found in the John W. 
McCutcheon, Inc. publication "Detergents and Emulsifiers Annual". The 
addition of a wetting agent to the composition can result in increased 
phytotoxicity. Consequently, if it is necessary to add a wetting agent to 
the composition, it generally should not exceed about 0.05 (v/v)% and 
preferably should not exceed about 0.03 (v/v)%. 
The compounds of the invention are generally applied to the area of 
treatment as herbicidal sprays by methods commonly employed, such as 
conventional high-gallonage hydraulic sprays, low gallonage sprays, 
airblast spray, aerial sprays and dusts. For low volume applications, a 
solution of the composition is usually used. The dilution and rate of 
application can be varied and will usually depend upon such factors as the 
type of equipment employed, the method of application, the area to be 
treated and the type and stage of development of the weeds.

EXAMPLE 1 
This example shows the significantly greater enhancement in herbicidal 
activity of sodium acifluorfen obtained by combining it with various 
citrates. 
Formulations of sodium acifluorfen were prepared by dissolving sodium 
acifluorfen in water in an amount to obtain about a 21 (w/v)% solution (Na 
acifluorfen-T) and by dissolving sodium acifluorfen and sodium citrate 
dihydrate in water to obtain concentrations of about 21 (w/v)% and 8.8 
(w/v)%, respectively (Na acifluorfen-C). Additional aqueous formulations 
were prepared by adding different citrate salts to these aqueous solutions 
of sodium acifluorfen. The formulations were tested under greenhouse 
conditions using the following test. Seeds of soybeans (Glycine max) and 
velvetleaf (Abutilon theophrasti) were planted in soil in plots. The seeds 
were allowed to germinate and after about two weeks the plots were treated 
with the test formulations. The day of treatment could vary within a 14-24 
day period following the planting of the seeds because plants of each crop 
and weed species were selected for uniformity, size and stage of 
development. The formulations were applied using a sprayer at a volume of 
25 to 50 gallons per acre. About two weeks after the test formulations 
were applied, the state of the growth of the plants was observed and the 
phytotoxic effect of each formulation was evaluated on a scale of 0 to 
100; 0 indicates no control and 100 indicates 100% control (complete 
control). The rates of application and typical results obtained are 
presented in Table 1. None of the citrates when applied alone cause any 
significant injury to either the soybeans or velvetleaf weeds. 
TABLE 1 
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Rate % 
lb/A % Injury Control 
Composition (Herb. + Salt) 
SOY VEL 
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Test 1 
Na Acifluorfen-C 
.25 0 30 
w/NH.sub.4 Citrate 
.25 + 1.0 4 68 
w/(NH.sub.4).sub.2 Citrate 
.25 + 1.0 3 83 
w/(NH.sub.4).sub.3 Citrate 
.25 + 1.0 3 85 
Test 2 
Na Acifluorfen-T 
.5 5 --* 
.25 -- 20 
.125 -- 5 
w/NH.sub.4 Citrate 
.5 + 1.0 18 -- 
.25 + 1.0 -- 98 
.125 + 1.0 -- 63 
w/(NH.sub.4).sub.2 Citrate 
.5 + 1.0 18 -- 
.25 + 1.0 -- 85 
.125 + 1.0 -- 60 
w/(NH.sub.4).sub.3 Citrate 
.5 + 1.0 15 -- 
.25 + 1.0 -- 88 
.125 + 1.0 -- 63 
w/Na Citrate .5 + 1.0 15 -- 
.25 + 1.0 -- 85 
.125 + 1.0 -- 50 
w/Na.sub.2 Citrate 
.5 + 1.0 15 -- 
.25 + 1.0 -- 65 
.125 + 1.0 -- 45 
w/Na.sub.3 Citrate 
.5 + 1.0 10 -- 
.25 + 1.0 -- 65 
.125 + 1.0 -- 25 
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*effect was not determined. 
EXAMPLE 2 
Using the same procedure as described in Example 1, the activities of 
sodium acifluorfen-T, sodium acifluorfen-C and each of these herbicides in 
conjunction with ammonium citrate were determined. An average of the 
results, expressed as an increase in percentage control over each 
herbicide alone, of the tests are provided in Table 2. 
TABLE 2 
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% Control 
Increase Over 
Rate the Acifluorfen 
No. of 
lb/A Alone Tests 
Composition 
Herb. + Salt 
SOY VEL Averaged 
______________________________________ 
Na Acifluorfen-T 
.25 + 1.0 4 48 13 
w/(NH.sub.4).sub.2 Citrate 
.25 + 2.0 16 59 3 
Na Acifluorfen-C 
.25 + 1.0 5 49 5 
w/(NH.sub.4).sub.2 Citrate 
.25 + 2.0 6 60 11 
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EXAMPLE 3 
The activities of sodium acifluorfen-T and sodium acifluorfen-C were 
determined in field tests. The procedure entailed preparing ground, which 
had a natural infestation of velvetleaf seeds from prior years, for 
planting of soybeans according to agronomical practices. About three weeks 
after the planting of the soybeans, when the soybeans were at their first 
trifoliate stage and the velvetleaf was at its two leaf stage, the field 
was divided into plots and different plots sprayed with each of the 
acifluorfens. About fourteen days after the application, the plants were 
observed and the phytotoxic effect of each formulation was evaluated on a 
scale of 0 to 100; 0 indicates no control and 100 indicates 100% control 
(complete kill). Typical results are presented below in Table 3 and show 
that there is no significant difference in the activities of these 
acifluorfens. 
TABLE 3 
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Rate % Injury % Control 
Composition lb/A SOY VEL 
______________________________________ 
Na Acifluorfen-T 
0.25 0 30 
0.50 4 67 
Na Acifluorfen-C 
0.25 3 35 
0.50 0 63 
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