Post emergence herbicidal compositions and methods for using same

Abstract

Combinations of a 2-nitro-5 (Substituted phenoxy) benzoic acid or derivative thereof, e.g. sodium acifluorfen with a derivative of 3,5-dihalo-4-hydroxybenzonitrile e.g. 3,5-dibromo-4-hydroxy-benzonitrile (bromoxynil, especially in a salt form), exhibit unexpected synergistic herbicidal activity against several important weed species when applied post-emergence in important agronomic crops.

What is claimed: 
     
       1. A herbicidal composition consisting essentially of: A. A compound selected from 2-nitro-5-substituted phenoxybenzoic acids, salts and alkyl esters thereof and 2-nitro-5-substituted pyridyloxybenzoic acids, salts and alkyl esters thereof of the following formula: ##STR3##  wherein: X is halogen; Y' is C(Y) or N; Y is hydrogen or halogen; Z is a halo-alkyl group of one or two carbon atoms;   R is selected from hydrogen, alkali metal and alkaline earth metal;     B. A compound selected from 3,5-dihalo-4-hydroxybenzonitrile derivatives of the formula ##STR4##  wherein X' is an iodine or bromine atom, preferably a bromine atom; R' is hydrogen, an alkali metal (e.g., Li, Na, K) an alkaline earth metal, ammonium, alkylammonium, dialkylammonium, or any other agronomically acceptable cation forming salt, or an alkanoyl (--COR 2 ) group wherein R 2  is an alkyl group of one to twenty saturated or unsaturated carbon atoms, wherein the weight ratio of the Compound A to Compound B component is in the range of 0.3 to 3.   
     
     
       2. A herbicidal composition according to claim 1 wherein Compound A is selected from the class of compounds defined by Y' being --CH═, X being chloro and Z being trifluoromethyl. 
     
     
       3. A herbicidal composition according to claim 2 wherein Compound A is selected from the class of compounds defined by R being an alkali metal. 
     
     
       4. A herbicidal composition according to claim 3 wherein Compound A is sodium acifluorfen. 
     
     
       5. A herbicidal composition according to claim 1 wherein Compound B is selected from the class of compounds defined by X' being bromo and R' being hydrogen, an alkali metal or --COR 2 . 
     
     
       6. A herbicidal composition according to claim 5 wherein R 2  is an alkyl group having eight carbon atoms. 
     
     
       7. A herbicidal composition according to claim 4 wherein Compound B is selected from the class of compounds defined by X' being bromo, R' being hydrogen, an alkali metal or --COR 2  wherein R 2  is an alkyl group having eight carbon atoms. 
     
     
       8. A herbicidal composition according to claim 7 wherein R' is potassium. 
     
     
       9. A method of controlling weed species in a growth medium for soybeans, said method comprising applying post-emergence to said soybeans and said weed species, a herbicidally effective quantity of a composition consisting essentially of: A. a 2-nitro-5-substituted phenoxybenzoic acid, salt or alkyl ester thereof or a 2-nitro-5-substituted pyridyloxybenzoic acid, salt or alkyl ester of the following formula: ##STR5##  wherein X is halogen; Y' is C(Y) or N; Y is hydrogen or halogen; Z is a haloalkyl group of one or two carbons; R is selected from hydrogen, alkali metal, and alkaline earth metal; and   B. a 3,5-dihalo-4-hydroxy-benzonitrile derivative of the formula: ##STR6##  wherein X' is an iodine or bromine atom, preferably a bromine atom; R' is hydrogen, an alkali metal (e.g., Li, Na, K) an alkaline earth metal, ammonium, alkylammonium, dialkylammonium, or any other agronomically acceptable cation forming salt, or an alkanoyl (--COR 2 ) group wherein R 2  is an alkyl group of one to twenty saturated or unsaturated carbon atoms wherein the weight ratio of the Compound A component to Compound B component is in the range of 0.3 to 3.   
     
     
       10. A method according to claim 9 wherein Compound A is sodium acifluorfen and Compound B is selected from the class of compounds defined by X' being bromo and R' being hydrogen, potassium or --COR 2  wherein R 2  is an alkyl group having from 4 to 8 carbon atoms. 
     
     
       11. A method according to claim 10 wherein said herbicidal composition is a tank mix. 
     
     
       12. A method according to claim 10 wherein said herbicidal composition is a premix. 
     
     
       13. A method according to claim 10 wherein the use rate of Compound A and Compound B together in said herbicidal composition is from about 280 g/ha to about 600 g/ha. 
     
     
       14. A method according to claim 10 wherein said composition is applied in a broadcast treatment method. 
     
     
       15. A method according to claim 13 wherein the rate is from about 400 to about 600 g/ha. 
     
     
       16. A herbicidal composition consisting essentially of: A. a phenoxy-benzoic acid or salt thereof; and   B. bromoxynil,   wherein the weight ratio of Component A to Component B is in the range of about 0.3 to 3.