BACKGROUND TO THE INVENTION Many herbicidal compositions exist which are effective in killing all vegetation or selective vegetation. Many are based on sophisticated chemicals, some of which are toxic to other life forms.

Acetic acid exhibits some effect as a herbicide while citric acid at high concentrations exhibits some effect as a herbicide. There have been suggestions to use acetic acid as a herbicide, e.g. DE 4 030 687 (Kast), which describes such use alone or in combination with tensides.

SUMMARY OF INVENTION The applicant has now found that synergistic compositions of acetic acid and citric acid may be employed as a contact herbicidal composition for controlling post-emergent vegetative growth. The essential components of the herbicidal compositions are edible materials and, hence, can be safely applied to vegetation without risk of harm to animals, including humans.

Accordingly, in one aspect, the present invention provides a novel aqueous herbicidal composition for contact kill of post-emergent vegetative growth, consisting essentially of acetic acid in an amount of from about 2 to about 10 wt%, citric acid in an amount of from about 1 to about 6 wt%, the acetic acid and citric acid being present in a synergistic weight ratio of about 1:0.1 to about 1:0.8, the composition being in fully diluted form ready to apply to post-emergent vegetative growth by spraying onto the vegetative

growth. The composition may be prepared by dilution with water from a concentrate. The composition may further contain up to about 0.5 wt% of a wetting agent.

In an additional aspect of the present invention, there is provided a method of controlling post-emergent vegetative growth, which comprises applying to the vegetative growth an aqueous herbicidal composition according to the invention wherein such desired degree of kill is a complete kill of the vegetative growth or a selected degree of kill. The herbicidal composition may be applied to the vegetative growth by spraying. The acetic acid and citric acid are present in the composition in proportions to achieve a desired degree of kill to the vegetative growth.

The compositions of the present invention further are effective as growth regulators for a variety of plants, inhibiting or stimulating growth of the plants according to the ratios of acetic acid and citric acid used. Combinations of acetic acid and citric acid show evidence of systemic activities on some species. Such method forms a further aspect of the present invention.

BRIEF DESCRIPTION OF DRAWINGS Figures 1 to 4 are graphical representations of rate responses to treatment of certain species with acetic acid, citric acid and mixtures thereof in experimentation reported in the Examples below.

GENERAL DESCRIPTION OF THE INVENTION By itself, acetic acid does not exhibit broadleaf weeds and grasses selectivity. However, in combination with citric acid, as provided herein, it is possible to selectively control a number of annual and perennial weeds, including broadleaf weeds in established lawns and pastures.

In the present invention, there is provided an aqueous herbicidal composition for contact kill of vegetative growth, consisting essentially of:

acetic acid in an amount of from about 2 to about 10 wt% and citric acid in an amount of from about 1 to about 6 wt%, the acetic acid and citric acid being present in a synergistic weight ratio of about 1:0.1 to about 1:0.8, the composition being in fully diluted form ready to apply to post-emergent vegetative growth by spraying onto the vegetative growth. Such composition may be prepared by dilution with water from concentrate. A small amount of a wetting agent, up to about 0.5 wt%, may be present.

Where uses of the composition of the invention include exposure to high temperatures, it may be desirable to retard evaporation of the aqueous composition by incorporating therein a proportion of a suitable oil, so that the composition is in the form of an emulsion. The emulsion then is spread on the vegetable requiring.

The composition of the invention is composed of natural and edible components, namely acetic acid and citric acid and hence, not only is efficacious as a herbicide, either for total or selective kill of vegetation, but is safe to use. In contrast, most herbicides require chemical synthesis and exhibit toxic side effects on animals.

The herbicidal composition provided herein is a contact herbicide, which may be applied by spraying above-ground portions of the weeds that it is desired to kill, providing a simple mode of administration.

The compositions of the present invention rapidly and consistently kill above-ground parts of weeds. Plant injury is observed within a few hours of application of the compositions of the invention and plant death within a few days.

The compositions of the invention may be employed to kill and control a wide variety of annual and perennial broadleaf weeds and grasses as well as mosses.

Representative vegetative growth includes: Annual Broadleaf Weeds Annual Grasses Black medic Crab grass Chickweed Foxtail spp.

Cinquefoil (rough) Lamb's-quarters Oxalis spp.

Ragweed spp.

Cocklebur Pigweed Curled Dock Fleabane spp.

Russian Thistle Wild Buckwheat Perennial Broadleaf Weeds Cinquefoil (Silvery) Dandelion Plantain spp.

Toadflax Tufted vetch Wild carrot Clover spp.

Hawkweed spp.

Annual Grasses Barnyardgrass Witchgrass Perennial Grasses Quackgrass Bluegrass The present invention is illustrated further by the following Examples:

Example 1 This Example illustrates the synergistic effect of acetic acid and citric acid in herbicidal compositions.

Field corn, Var. Trucker's Favourite, was used as a representative test species, since the combination of acetic acid and citric acid is a non-selective herbicide and field corn is a fast growing plant, easily grown under greenhouse conditions and is representative of grass or weeds.

Field corn was direct seeded into four inch paper pots containing HYPONEXB, a soil based growing medium.

One seed was planted per pot. The pots were then incubated in a greenhouse. Plants were watered at least once daily on an as-needed basis. Greenhouse temperatures ranged from 62" to 890F throughout the growth and test period. Seed germination occurred within 4 days of planting. Field corn was at the two leaf stage (14 days after planting) at the time of treatment.

The experiments consisted of the following compositions: (1) Product A (acetic acid) at 10, 8.0, 6.0, 4.0 and 2.0 wt% (2) Product B (citric acid) at 6.0, 4.8, 3.6, 2.4 and 1.2 wt%.

(3) Mixtures of Product A + Product B at five levels, at a weight ratio of acetic acid to citric acid of 1:0.6: A B 10.0 + 6.0% 8.0 + 4.8 6.0 + 3.6 4.0 + 2.4 2.0 + 1.2

(4) Mixtures of Product A + Product B at five levels, at various ratios of acetic acid to citric acid: A B Ratio 4.0 + 3.2% 1:0.8 4.0 + 1.2 1:0.3 4.0 + 0.8 1:0.2 4.0 + 0.4 1:0.1 (5) Non-treated Control Surfactant (Product C) was added to each composition, including the non-treated control, at 0.1% of the finished spray.

Six replicates were included for each composition.

The compositions were prepared in deionized water and applied to foliage using a hand-held CO2 pressurized sprayer fitted with a Teejet 8001 nozzle and delivering the equivalent of 50 gallons per acre (foliar spray to near run-off) . A non-treated control (water + surfactant) was included.

Applications were made using a spray pressure of 25 PSI. The spray plot area was 36" x 18" and the plants were arranged within the plot area and the application applied by volume (20 ml/plot). The non-treated controls received the equivalent amount of water with surfactant but with no chemical added.

The daily greenhouse temperatures ranged from approximately 65"F at night to 850F during the day. The greenhouse heating was set so that the temperature did not fall below 650F.

Visual assessments were made of the percent necrosis of the whole plant at three days after treatment. The Barrat-Horsfall rating system was used to estimate the amount of plant injury. This rating system is a weighed, 0 to 11 rating scale with 0 being no injury and 11 being 100% injury. On the seventh day, the fresh weight of the plants were taken by cutting

plants within treatment replicates at soil level. The fresh weight of each replicate was recorded.

The effect of the rate of the test composition on plant injury and fresh weight was related to the non- treated control. The Barrat-Horsfall numerical injury ratings were converted to estimated mean percent injury using a conversion table developed by Redman King and Brown, Eli Lilly and Company. All plant fresh data were entered into Quattro PRO WINDOWS (version 6.0) spreadsheet, to calculate mean values. All raw data were analyzed by analysis of variance (ANOVA 2-Way) using Quattro Pro version 6.0 program. If a significant F-Test at p = 0.05 was found between the composition concentrations and the observations, then the composition mean values were separated by utilizing LSD mean separation test. ED25 and ED50 (Effective Dose that cause a 25 and 50 percent reduction in the parameter measured) values were determined by regression and probit analysis using Lotus 1, 2, 3 software.

The results which were obtained in this experimentation were tabulated and are presented in Tables I, II and III below. As may be seen from this data, acetic acid applied alone at 10, 8, 6, 4 and 2% showed a rate responsive effect for both plant injury and plant fresh weight. The highest rate, 10%, of acetic acid alone caused 39% plant injury and 29% reduction in plant fresh weight. An ED25 value of 7.5% was calculated for plant injury; an ED50 value could not be determined. For fresh weight reduction, an ED25 value of 22.7% was extrapolated from the data. Citric acid at the rates tested, 6, 4.8, 3.6, 2.4 and 1.2%, was only weakly active causing only slight injury and no reduction in plant fresh weight. The rates tested were too low to allow an ED25 or an ED50 to be determined for either parameter.

When used in mixtures, acetic acid and citric acid were more effective than either alone and, therefore, synergistic. The synergistic interaction between acetic and citric acid is apparent from a comparison of rate response curves prepared from the raw data and the ED25 values (Table III). Acetic acid alone showed an ED25 of 7.5 for plant injury, citric acid was ineffective at the highest rate tested and the combination had an ED25 of 2.6. This result is an increase in activity of approximately three-fold as compared to acetic acid alone at the same concentration. Similar results were obtained on the effects on fresh weight. Acetic acid alone had little effect on plant weight and an ED25 value was extrapolated to be 22.7; the ED25 for the mixture of acetic acid and citric acid was 9.7, a 2.5 fold increase as compared to activity of acetic acid alone.

Four mixtures of acetic acid and citric acid were tested to determine the effect of modification of their weight ratio on herbicidal activity. Acetic acid was included in each of the test mixtures at a single rate of 4.0%. Citric acid was added to produce the following weight ratios: 1:0.8, 1:0.3, 1:0.2 and 1:0.1. Under the conditions of this test, acidic acid alone at 4.0% provided only minimal activity, causing some phytotoxic effects but no effect on the fresh weight of the plants over the seven day course of the test. It is apparent that the combinations of acetic acid and citric acid are synergistic in all the ratios tested. The most effective combination found in these tests was 1 part acetic acid to 0.8 parts citric acid.

It can be seen, therefore, from these experiments that acetic acid was more effective as a herbicide when mixed with citric acid than when applied alone.

Assessment of the percent control showed that synergistic action occurred for control of corn when

acetic acid and citric acid were mixed. The herbicidal activity of acetic and citric acid was 2.5 to 3 times greater in combination than either materiai applied alone. The combination of the two materials was synergistic over a wide range of concentrations. The compositions further showed a growth regulation capacity, as seen from Table II.

Example 2: This Example illustrates the synergistic effect on selected broadleaf and grassyweed species of acetic acid and citric acid in herbicidal compositions.

The following weed species were used for the tests described in this Example: Common Name Scientific Name Broadleaf weeds Cocklebur Xanthium pensylvanicum Pigweed, redroot Ama ran thus retoflexus Grassy weed Green Foxtail Setaria virdis Woody Perennial Russian olive Elaeagnus angustifolia Cocklebur, pigweed and green foxtail were direct seeded into 8 x 4 inch paper flats containing HYPONEXB, a soil based growing medium. Cocklebur and pigweed seed were sown into one row each; about 15 to 20 seed per row. Green foxtail was planted into a separate flat in a single row. The row was heavily seeded. The planted flats were then incubated in the greenhouse. Three year old Russian olive plants (40 plants) were purchased and placed in the greenhouse. Plants were watered at least once daily on an as needed basis. Greenhouse temperatures ranged from 650F to 920F throughout the growth and test period. The plants were grown under greenhouse conditions for 29 days before being used in the test. Seed germination was adequate and the flats were thinned to approximately 3 to 5 cocklebur and 3 to

6 pigweed in each row. Foxtail was solid seed and produced a heavy plant stand. At test initiation the cocklebur was at the 4 to 6 six leaf stage, pigweed was at the 8 to 10 leaf stage and the foxtail was at the seed head stage of development. The Russian olive plants were approximately 3 years old (16 to 20" high) and received in two gallon plastic pots.

The experiments consisted of the following compositions: (1) Product A (acetic acid) at 12.0, 10.0, 8.0, 6.0, and 4.0% (2) Product B (Citric acid) at 7.2, 6.0, 4.3, 3.6 and 2.4% (3) Mixture of Product A + Product B at five levels, maintaining a ratio of acetic acid:citric acid of 1:0.6: A B 12.0 + 7.2 10.0 + 6.0% 8.0 + 4.8 6.0 + 3.6 4.0 + 2.4 (4) Mixture of Product A and Product B at 1 part mixture: 3 parts water (6.25% + 3.1% acetic acid:citric acid).

(5) Non-treated Control Surfactant was added to each treatment, including the non-treated control at 0.1% of the finished spray.

Surfactant was not added to the Product 4 treatment.

Two replicate flats or pots were included for each treatment rate. The compositions were prepared in deionized water and applied to foliage using a hand held CO2 pressurized sprayer fitted with a Teejet 8001 nozzle and delivering the equivalent of 50 gallons per acre (foliar spray to near run-off). A non-treated control (water + surfactant) was included.

Applications were made using a spray pressure of 25 PSI. The spray plot area was 36" x 18" and the plants were arranged within the plot area and the application applied by volume (20 ml/plot). The non-treated controls received the equivalent amount of water with surfactant but with no chemical added.

The daily greenhouse temperatures ranged from approximately 65"F at night to 920F during the day. The greenhouse heating was set so that the temperature did not fall below 650F.

Visual assessments were made of the percent necrosis of the whole plant at three days after treatment. The Barrat-Horsfall rating system was used to estimate the amount of plant injury.

The effect of the rate of the test compound on plant injury was related to the non-treated control. The Barrat-Horsfall numerical injury ratings were converted to estimated mean percent injury using a conversion table developed by Redman King and Brown, Eli Lilly and Company. All plant injury data were entered into Quattro PRO WINDOWS (version 6.0) spreadsheet, to calculate treatment means. All raw data were analyzed by analysis of variance (ANOVA 2-Way) using Quattro Pro version 6.0 program. If a significant F-Test at p = 0.05 was found between the treatment concentrations and the observations, then the treatment means were separated by utilizing LSD mean separation test. ED25 and ED50 values were determined by regression and probit analysis using Lotus 1,2,3 software.

Acetic acid applied alone at 12, 10, 8, 6, and 4% showed a rate responsive effect for plant injury (herbicidal activity) on all of the weed species (Tables IV, V, VI and VII).

Citric acid at the rates tested, 6, 4.8, 3.6, 2.4 and 1.2%, was inactive or only weakly active. Citric

acid caused only slight injury to pigweed and cocklebur and no injury to green foxtail or Russian olive.

When used in mixtures, acetic acid and citric acid were more effective than either alone and, therefore, synergistic. The synergistic interaction between acetic and citric acid is apparent from the comparison of the rate response curves (Figures 1, 2, 3 and 4) and the ED50 values (Table VIII). An ED50 value could not be determined for the perennial species, Russian olive because of the lower activity of ECO-N-SELECT against this species. For the annual weed species, the increase in activity of the mixture of acetic and citric acid over acetic acid alone is in the range of approximately 20 to 40% (at the ED50 values).

Results from these experiments indicate that acetic acid was more effective as a herbicide when mixed with citric acid then when applied alone. Assessment of the percent control and regression lines showed that synergistic action occurred for control of all weed species tested when acetic and citric acids were mixed.

The herbicidal activity was 20 to 40% greater (when measured at the ED50 value) in combination than either material applied alone. The combination of the two materials is synergistic over a wide range of concentrations as evidenced by the regression response lines.

SUMMARY OF DISCLOSURE In summary of this disclosure, the present invention relates to a novel herbicidal composition comprising synergistic combinations of acetic acid and citric acid, which are diluted with water to provide the desired herbicidal properties. Modifications are possible within the scope of this invention.

TABLE I SYNERGISTIC HERBICIDAL EFFECTS OF MIXTURES OF ACETIC AND CITRIC ACID. PHYTOTOXICITY RATING OF CORN PLANTS THREE DAYS AFTER TREATMENT TREATMENT RATE (%) AVE. % PHYTO t ACETIC ACID 10.0 45 8.0 10 6.0 4 4.0 3 2.0 2 CITRIC ACID 6.0 2 4.8 2 3.6 2 2.4 1 1.2 0 ACETIC + CITRIC 10.0 + 6.0 96 8.0 + 4.8 79 6.0 + 3.6 53 4.0 + 2.4 21 2.0 + 1.2 4 ACETIC + CITRIC 4.0 + 3.2 41 4.0 + 1.2 24 4.0 + 0.8 14 4.0 + 0.4 13 CONTROL 0.0 0 t Injury rated, using Barrat-Horsfall System, on a 1 to 11 scale with 0 being no injury and 11 being 100% injury.

TABLE II SYNERGISTIC HERBICIDAL EFFECTS OF MIXTURES OF ACETIC AND CITRIC ACID. FRESH WEIGHT OF CORN PLANTS SEVEN DAYS AFTER TREATMENT TREATMENT RATE (%) AVE. WT (g) STD DEV ACETIC ACID 10.0 1.57 0.51 8.0 2.65 0.58 6.0 1.82 0.48 4.0 2.02 0.74 2.0 2.20 0.39 CITRIC ACID 6.0 2.57 0.48 4.8 2.25 0.50 3.6 2.57 0.51 2.4 2.22 0.33 1.2 2.70 0.53 ACETIC 10.0 + 6.0 0.82 0.19 + 8.0 + 4. 8 2.22 0.42 CITRIC 6.0 + 3.6 2.73 0.73 4.0 + 2.4 2.92 1.25 2.0 + 1.2 3.15 1.21 ACETIC 4.0 + 3.2 2.65 0.64 + 4.0 + 1.2 2.55 0.69 CITRIC 4.0 + 0.8 2.63 0.88 4.0 + 0.4 3.67 1.56 CONTROL 0.0 2.22 0.39 TABLE III PLANT INJURY AND FRESH WEIGHT, ED25 AND ED50 IN % a.i. TREATMENT/PARAMETER ED25 ED50 Acetic Acid Alone Plant Injury 7.5 ND Fresh Weight 22.7 t ND Citric Acid Alone Plant Injury ND ND Fresh Weight ND ND Acetic + Citric Plant Injury 2.6 5.3 Fresh Weight 5.3 10.5 ND = Not Determined t = Extrapolated Value TABLE IV SYNERGISTIC HERBICIDAL EFFECTS OF MIXTURES OF ACETIC AND CITRIC ACID. PHYTOTOXICITY RATING OF COCKLEBUR SEVEN DAYS AFTER TREATMENT TREATMENT RATE (%) AVE. % PHYTO t ACETIC ACID 12.0 98.8 10.0 100.0 8.0 62.5 6.0 85.9 4.0 4.7 CITRIC ACID 7.2 4.7 6.0 3.5 4.8 2.3 3.6 0.0 2.4 0.0 ACETIC + CITRIC 12.0 + 7.2 96 10.0 + 6.4 79 8.0 + 4.8 53 6.0 + 3.6 21 4.0 + 2.4 ECO-N-SELECT# 7.5 + 3.8 91 CONTROL 0.0 0 tInjury rated, using Barrat-Horsfall System, on a 1 to 11 scale with 0 being no injury and 11 being 100% injury.

# Applied at the recommended field use rate of 300 ml ECO-N-SELECT + 700 ml water.

TABLE V SYNERGISTIC HERBICIDAL EFFECTS OF MIXTURES OF ACETIC AND CITRIC ACID. PHYTOTOXICITY RATING OF PIGWEED SEVEN DAYS AFTER TREATMENT TREATMENT RATE (%) AVE. % PHYTO t ACETIC ACID 12.0 98.8 10.0 100.0 8.0 62.5 6.0 85.9 4.0 4.7 CITRIC ACID 7.2 4.7 6.0 3.5 4.8 2.3 3.6 0.0 2.4 0.0 ACETIC + CITRIC 12.0 + 7.2 96 10.0 + 6.4 79 8.0 + 4.8 53 6.0 + 3.6 21 4.0 + 2.4 ECO-N-SELECT# 7.5 + 3.8 91 CONTROL 0.0 0 tInjury rated, using Barrat-Horsfall System, on a 1 to 11 scale with 0 being no injury and 11 being 100% injury.

# Applied at the recommended field use rate of 300 ml ECO-N-SELECT + 700 ml water.

TABLE VI SYNERGISTIC HERBICIDAL EFFECTS OF MIXTURES OF ACETIC AND CITRIC ACID. PHYTOTOXICITY RATING OF GREEN FOXTAIL SEVEN DAYS AFTER TREATMENT TREATMENT RATE (%) AVE. % PHYTO t ACETIC ACID 12.0 98.8 10.0 100.0 8.0 62.5 6.0 85.9 4.0 4.7 CITRIC ACID 7.2 4.7 6.0 3.5 4.8 2.3 3.6 0.0 2.4 0.0 ACETIC + CITRIC 12.0 + 7.2 96 10.0 + 6.4 79 8.0 + 4.8 53 6.0 + 3.6 21 4.0 + 2.4 ECO-N-SELECT# 7.5 + 3.8 91 CONTROL CONTROL 0.0 0 tInjury rated, using Barrat-Horsfall System, on a 1 to 11 scale with 0 being no injury and 11 being 100% injury.

# Applied at the recommended field use rate of 300 ml ECO-N-SELECT + 700 ml water.

TABLE VII SYNERGISTIC HERBICIDAL EFFECTS OF MIXTURES OF ACETIC AND CITRIC ACID. PHYTOTOXICITY RATING OF RUSSIAN OLIVE SEVEN DAYS AFTER TREATMENT TREATMENT RATE (%) AVE. % PHYTO t ACETIC ACID 12.0 38 10.0 19 8.0 19 6.0 10 4.0 5 CITRIC ACID 7.2 0.0 6.0 0.0 4.8 0.0 3.6 0.0 2.4 0.0 ACETIC + CITRIC 12.0 + 7.2 50 10.0 + 6.4 38 8.0 + 4.8 19 6.0 + 3.6 5 4.0 + 2.4 2 ECO-N-SELECT# 7.5 + 3.8 15 CONTROL 0.0 0 tInjury rated, using Barrat-Horsfall System, on a 1 to 11 scale with 0 being no injury and 11 being 100% injury.

# Applied at the recommended field use rate of 300 ml ECO-N-SELECT + 700 ml water.

TABLE VIII EFFECT DOSAGE VALUES AT ED25 AND ED5o IN % ACTIVE INGREDIENT FOR COCKLEBUR, PIGWEED AND GREEN FOXTAIL.

SEVEN DAY DATA. TREATMENT/Weed Species ED25 ED50 Acetic Acid Alone Cocklebur 3.2 5.8 Pigweed 5.6 8.4 Gr. Foxtail 3.6 6.3 Citric Acid Alone Cocklebur ND ND Pigweed ND ND Gr. Foxtail ND ND Acetic + Citric Cocklebur 0.7 3.7 Pigweed 4.3 6.8 Gr. Foxtail 2.4 5.0 ND = Not Determined > 7.2% (highest rate tested)