Patent Publication Number: US-4923853-A

Title: Process for enhancing the activity of plant protecting agents by using cyclodextrin

Description:
This is a continuation of co-pending application Ser. No. 916,484 filed on 8 Sept. 1986 now abandoned. 
    
    
     TECHNICAL FIELD 
     This invention relates to new and improved plant protecting agents, particularly fungicidal compositions and a method for the use thereof. 
     BACKGROUND ART 
     Recently several articles and patents have been published relating to the use of cyclodextrin in plant protecting formulations [Novenyvedelem, 19, 364 (1983); J. Szejtli: Cyclodextrins and their Inclusion Complexes, Akademiai Kiado, Budapest, 1982]. On forming complexes of molinate (S-ethyl-N,N-hexamethylene-thiocarbamate), bentiocarb (S-4-chlorobenzyl-diethylthio carbamate) and dichlorphos (2,2--dichlorovinyl-dimethyl-phosphate) the volatility of the active ingredient is significantly decreased and the activity of the pesticide remains sufficient for a longer period of time [Mikasa Chemical Industrial Co; KOKAI No. 80.81806; DOS No. 2,422,316 (1974); Acta Chem. Acad. Sci. Hung. 107, 195 (1981)]. Methyl-parathion (0,0-dimethyl-0-4-nitrophenyl-phosphorothioate) and natural pyrethrines and pyrethroides, respectively, are converted into the cyclodextrin A 3673/77-OE complexes in order to increase the stability against light and oxygen to a considerable extent [Pestic. Sci. 11, 134 (1980); U.S. Pat. No. 3,846,551 (1974);Nippon Noyaku Gakkaishi 1, 41 (1976); 2, 41 (1977)]. The dichlobenyl (2,6-dichloro-benzonitrile) active ingredient easily sublimates and on standing the granulated product sticks together; this can be inhibited by forming complex with cyclodextrin [5th Int. Cong. Pesticide Chem. (IUPAC) Kyoto (1983)]. 
     The complex formation of 2-chloromethane-phosphonic acid with cyclodextrin results in the fact that on contacting with plant tissue the ethylene release is a long-lasting process and this is more efficient than the delivery of ethylene from a very promptly acting active ingredient [Acta Chim. Acad. Sci. Hung. 107, 231 (1981)]. 
     DISCLOSURE OF THE INVENTION 
     It was not aforeseen from the prior art that cyclodextrin would synergize the efficiency of fungicides. 
     The object of the present invention is to provide fungicidal compositions comprising cyclodextrin in which cyclodextrin synergizes the activity of known fungicidal active ingredients to a significant extent. Thus identical fungicidal active ingredient dosage results in a higher activity or the same fungicidal effect can be achieved by using a lower dose of the active ingredient and this is a considerable advantage from the point of view of both economy and the safety of environment. 
     According to an aspect of the present invention there is provided a fungicidal plant protecting composition comprising 3-90% by weight of a fungicidal active ingredient in admixture with 1-90% by weight of cyclodextrin and optionally with usual auxiliary agents. 
     In the fungicidal composition according to the present invention the ratio of the fungicidal active ingredient and cyclodextrin amounts to 90:1-1:5, preferably 2-5:1. 
     The composition according to the present invention may preferably comprise the following fungicidal active ingredients: 
     benomyl=1-butylcarbamoyl-benzimidazole-2-methyl-carbamate; 
     BCM=2-carbomethoxyamino-benzimidazole; 
     metomeclan=1-(3,5dichlorophenyl)-3-methoxy-methyl-pyrrolidine-2,5-dione; 
     phenarimol=2,4&#39;-dichloro-α-(pyrimidine-5-yl)--diphenyl-methanol. 
     As cyclodextrin α-, β- and/or γ-cyclodextrin may be used. 
     According to a preferable embodiment of the present invention the ratio of the above active ingredients and cyclodextrin may be as follows: 
     benomyl:cyclodextrin=2-5:1 
     BCM:cyclodextrin=2-5:1 
     metomeclan:cyclodextrin=2-20:1 
     phenarimol:cyclodextrin=1-100:10. 
     According to a further aspect of the present invention there is provided a fungicidal method of treatment which comprises applying onto the plants or the other surface to be treated a composition according to the present invention, preferably at a rate of 0.5-6 kg/ha, particularly 1.2-1.6 kg/ha. 
     The present invention is based on the recognition that known fungicidal active ingredients and cyclodextrin exhibit a synergistic effect which is a result of one or two of the following factors: 
     the fungistatical activity of cyclodextrins themselves; 
     the solubility increasing effect of cyclodextrins. 
     The fungistatical activity of cyclodextrins has never been disclosed in prior art. The said activity may be proved by the following test: 
     Agar nutrient media comprising 0.1-0.2 -0.5-1.0-2.0-5.0-10.0-20.0-100.0- 200.0-400.0-800.0-1200.0-1500.0-2000.0-3000.0 μg β-cyclodextrin/ml, respectively, are prepared in Petri-dishes. Mycelium discs are cut out from surface cultures of three test fungi and are placed onto the agar nutrient media in the Petri-dishes. Incubation is carried out in a thermostate whereupon the increase of the diameter of the colonies is determined and compared to that of the control. The morphology of the colonies and the diffusion of the dye-substance produced by the fungi into the nutrient medium are evaluated as well. The results are summarized in Table 1. 
     
                       TABLE 1                                                     
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Fungistatical effect of β-cyclodextrin                               
         Inhibition %                                                     
         Microorganisms                                                   
           Rhizoctonia Sclerotinia                                        
                                  Alterna-                                
Concentration                                                             
           solani      sclerotiorum                                       
                                  ria tenuis                              
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3000       19          16         14                                      
1500       17          14         12                                      
 400        6          12         10                                      
 200        3          12          7                                      
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     In a dose range of 0.1-20 μg/ml the effect of β-cyclodextrin is of a qualitative character. The fungistatical effect of cyclodextrin manifests itself in the changed morphology, structure and color of the colonies and in the amount of the dyestuff penetrated into the nutrient medium. However at higher dose range the effect of cyclodextrin is already of a quantitative nature, thus the decrease of the diameter of the colonies can be measured and the amount of the biomass formed is reduced to a rate which can be evaluated (Table 1). A study of the surfacial cultures show that β-cyclodextrin inhibits the formation of the propagative organs. 
     The main feature of the solubility increasing effect of cyclodextrin due to the formation of inclusion complexes resides in the fact that in aqueous solution beside the molecularly dispersed (i.e. actually dissolved) active ingredient and the mycelia consisting of some or a lot of molecules (microcrystal, microdrop), the cyclodextrin-active ingredient inclusion complex being also in molecularly dispersed form appears, too. 
     Since the said system is characterized by an unusually dynamical equilibrium (within 10 -8  sec -1 ) the active ingredient incorporated into the inclusion complex acts in the same way from the point of view of absorption as the free dissolved active ingredient. 
     Thus the concentration of molecularly dispersed molecules being suitable for direct absorption may be significantly increased with the aid of cyclodextrins and this accelerates the rate of absorption, i.e. the same efficiency can be achieved by using a lower active ingredient dose. 
     The positive effect of cyclodextrin on the solubility of active ingredients is shown on the example of benomyl. The said active ingredient (1-butylcarbamoyl-benzimidazole-2-methyl-carbamate) is a systemic fungicide, which is poorly soluble in water and when dissolved in water rapidly decomposes to methyl-benzimidazole carbamate having also a fungicidal effect but being still less soluble in water. 
     On shaking benomyl and benomyl+cyclodextrin, respectively, in water at 25° C. the solubility data summarized in Table 2 are obtained. (Benomyl and benomyl+β-cyclodextrin, respectively, are shaken in water at 25° C., the samples are filtered and the dissolved benomyl contents of the filtrates are determined by UV spectrophotometry). 
     
                       TABLE 2                                                     
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Increase of the solubility of benomyl                                     
under the effect of β-cyclodextrin                                   
Time of                                                                   
experiment                                                                
         Amount of dissolved benomyl                                      
(minutes)                                                                 
         μg/ml  %         μg/ml                                     
                                     %                                    
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                     Weighed in: 170 μg of                             
       Weighed in: 1000 μg/ml                                          
                     benomyl + 830 μg/ml                               
       of benomyl    of β-CD                                         
10       2         0.2        7      4.1                                  
20       3         0.3        9      5.3                                  
40       4.5       0.45      10      5.9                                  
80       5         0.5       12      7.0                                  
120      5         0.5       13      7.6                                  
                     Weighed in: 850 μg of                             
       Weighed in: 5000 μg/ml                                          
                     benomyl + 4150 μg/ml                              
       of benomyl    β-CD                                            
10       3.5       0.07      12      1.4                                  
20       4         0.08      16      1.9                                  
40       6         0.12      17      2.0                                  
80       8         0.16      18      2.1                                  
120      9.5       0.19      19      2.2                                  
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     Benomyl is put on the market under the commercial name Fundazol 50 WP; benomyl active ingredient content: 50%. In Table 3 the solubility data of benomyl, a mixture of benomyl and cyclodextrin, Fundazol 50 WP, and a mixture of Fundazol 50 WP and cyclodextrin are shown. In each experiment 3000 μg/ml of the test substance are weighed in and shaken at 25° C. Benomyl is a 100% active ingredient; the benomyl content of the benomyl/cyclodextrin mixture amounts to 17.3%; the benomyl content of Fundazol 50 WP is 50%; the benomyl content of the mixture of Fundazol 50 WP and cyclodextrin amounts to 8.65%. It appears from Table 3 that as a result of the formulation the solubility of benomyl is increased four times. 
     Cyclodextrin per se causes a further 1.5-2-fold increase of the solubility of both original benomyl and formulated Fundazol 50 WP. Taking into consideration that in the mixtures comprising cyclodextrin the amount of benomyl active ingredient is considerably lower and at the same time in aqueous solution the concentration of benomyl being responsible for the actual biological effect became significantly higher, it was aforeseen that this had to be manifested in the biological effect, too. 
     
                       TABLE 3                                                     
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Increase of the solubility of benomyl from Fundazol under the             
effect of β-cyclodextrin                                             
Time of  Dissolved benomyl (μg/ml)                                     
experiment         Benomyl +         Fundazol +                           
(minutes)                                                                 
         Benomyl   BCD       Fundazol                                     
                                     BCD                                  
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10       2          5        27      40                                   
20       5          8        28      42                                   
40       6         11        29      44                                   
80       7         13        30      46                                   
120      8         13        31      48                                   
160      9         13        32      49                                   
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     The solubility of benomyl from various materials comprising benomyl was determined by shaking in water at 25° C. 2000 μg/ml of solid material are weighed in which corresponds to the following amounts of benomyl: 
     in the case of benomyl: 2000 μg/ml 
     in the case of benomyl+β-CD: 350 μg/ml++1650 μg β-CD 
     in the case of Fundazol 50 WP: 1000 μg/ml 
     in the case of Fundazol 50 WP+β-CD: 175 μg/ml++1650 μg β-CD. 
     The following tests substantiate the surprising synergism between known fungicides and β-cyclodextrin. Stable, highly dispersed aqueous suspensions of the test materials are added to agar nutrient media in the desired concentration (0.1-200 μg/ml), whereupon the nutrient media are poured into Petri-dishes. Mycelium discs are cut out from the surfacial cultures of the test fungi and the discs are placed into the Petri-dishes containing the test materials. Incubation is carried out in thermostate whereupon the increase of the diameter of the colonies is measured and and compared to that of the control. The tests are carried out in three replicates. 
     In Table 4 the effect of the fungicide Fundazol 50 WP (benomyl content 50%) and a mixture of Fundazol 50 WP+10% of β-cyclodextrin is disclosed. The results clearly prove the synergistic activity of β-cyclodextrin; the increased activity is particularly significant against Botrytis cinerea and Monilia fructigena. 
     
                       TABLE 4                                                     
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Fungicidal activity of Fundazol and                                       
recrystallized β-cyclodextrin                                        
           ED.sub.50 (μg/ml,                                           
           related to active ingredient                                   
                      Fundazol +   Increase of                            
Microorganism                                                             
             Fundazol 10% β-CD                                       
                                   activity (x)                           
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Rhizoctonia solani                                                        
             0.87     0.64         1.3                                    
Sclerotinia sclerotiorum                                                  
             0.12     0.05         2.4                                    
Fusarium moniliforme                                                      
             0.88     0.38         2.3                                    
Botrytis cinerea                                                          
             0.14      0.0125      10.2                                   
Ascochyta pisi                                                            
             0.72     0.25         2.9                                    
Fusarium culmorum                                                         
             0.77     0.44         1.7                                    
Colletotrichum lini                                                       
             0.68     0.5          1.3                                    
Monilia fructigena                                                        
             0.05      0.0125      4.0                                    
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     Metomeclan is a contact fungicide insoluble in water [1-(3,5-dichlorophenyl)-3-methoxymethyl-pyrrolidine-2,5-dione]. The activity of metomeclan is significantly increased by the addition of cyclodextrin. In Table 5 the fungicidal effect of metomeclan and a mixture of metomeclan +10% of β-CD is set forth. 
     
                       TABLE 5                                                     
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Increase of activity of metomeclan Additional                             
adding 10% of β-cyclodextrin                                         
           ED.sub.50 (μg/ml,                                           
           related to active ingredient                                   
                        Metome-                                           
                        clan +     Increase of                            
Test microorganism                                                        
             Metomeclan 10% of β-CD                                  
                                   activity (x)                           
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Fusarium moniliforme                                                      
             12         7          1.7                                    
Alternaria tennis                                                         
             2.9        1.8        1.6                                    
Stemphylium  5.7        3.9        1.5                                    
radicinum                                                                 
Rhizoctonia solani                                                        
             3.3        2.3        1.4                                    
Colletotrichum lini                                                       
             25.5       8.9        2.9                                    
Ascochyta pisi                                                            
             4.6        2.8        1.6                                    
Fusarium culmorum                                                         
             16.5       7.5        2.2                                    
Alternaria crassa                                                         
             3.9        2.2        1.8                                    
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     In vivo tests are carried out on wheat-powdery mildew (host-parasite) by using a combination of phenarimol [2,4&#39;-dichloro-α--(pyrimidine-5-yl)-diphenyl-ethanol] and β-cyclodextrin. The tests are carried out in three replicates in phytotrone under usual experimental system and environmental conditions (20° C., humidity 90%, light intensity 9000 lux.) In culturing dishes (diameter 11 cm) as average 160 plants (5-6 cm stage) are treated with 8 ml of stable aqueous suspensions comprising the test material. The results are summarized in Table 6 . The inhibition activity is calculated on the basis of the Hinfner-Papp formula by using the infectedness index. 
     
                       TABLE 6                                                     
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cyclodextrin on phenarimol + β                                       
wheat powdery mildew host parazite                                        
Phenarimol  Inhibition activity %                                         
CDncentration          Phenarimol + β                                
μg/ml    Phenarimol (ratio 1:5)                                        
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10          100.0      100.0                                              
5           99.4       100.0                                              
2.5         87.2       98.2                                               
1.25        73.5       83.2                                               
0.625       29.4       42.3                                               
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     In a further series of experiments it is tested whether known linear dextrins obtained by thermal, enzymatic or acidic decomposition of starch exhibit similar effects as cyclodextrins. The said tests show unambiguously that only cyclodextrins possess the above fungicidal-synergizing activity. 
     INDUSTRIAL APPLICABILITY 
     As a result of the synergizing effect of cyclodextrins the dosage of known and generally used fungicidal active ingredients can be significantly decreased under achieving identical or even increased fungicidal effect and this decreases the costs involved with the active ingredients and reduces the risks of environmental pollution as well. 
     MODES OF CARRYING OUT THE INVENTION 
     Further details of the present invention are to be found in the following Examples without limiting the scope of protection to the said Examples. 
    
    
     EXAMPLE 1 
     Spray Comprising Benomyl As Active Ingredient 
     Benomyl is put on the market as spray in the form of a wettable powder having an active ingredient content of 50% under the commercial name Fundazol 50 WP. A product having the same activity but containing a smaller amount of active ingredient is prepared as follows: 
     35 kg of benomyl pre-micronized in an air-flow mill and 15 kg of crystalline β-cyclodextrin (moisture content 13%) also pre-micronized in an air-flow mill are admixed with 40 kg of precipitated calcium carbonate, 5 kg of sulfide waste powder and 5 kg of an anionic tenside containing 50% of water (preferably Genapol PGM, pre-heated to 50° C.) in a homogenizer. The homogenized material is dried, micronized in order to separate the particles stocked together and finally packed. 
     EXAMPLE 2 
     One proceeds according to Example 1 i.e. the components are micronized, homogenized, dried and re-micronized. The composition is as follows: 
     
         ______________________________________                                    
Benomyl (related to 100% active                                           
                         40     kg                                        
ingredient)                                                               
Precipitated calcium carbonate                                            
                         40     kg                                        
Tensiofix BC.sub.2       2.5    kg                                        
Totamine                 5      kg                                        
β-Cyclodextrin      12.5   kg                                        
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     EXAMPLE 3 
     Seed-Treating Composition Comprising Benomyl As Active Ingredient 
     One proceeds according to Example 1. The composition is as follows: 
     
         ______________________________________                                    
Benomyl                  35     kg                                        
Diotilan                 1      kg                                        
Evidet 27                1      kg                                        
Tylose N 20              1      kg                                        
Aerosil &#34;300&#34;            0.5    kg                                        
Safranin P extra         2      kg                                        
Spray-dried crude converted cyclo-                                        
                         38     kg                                        
dextrin mixture (β-cyclodextrin                                      
cyclo-t about 48%; α- and γ                                   
dextrin content 2%, partially de-                                         
composed starch content about 50%)                                        
Precipitated calcium carbonate                                            
                         21.5   kg                                        
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     EXAMPLE 4 
     Seed-Treating Composition Comprising Abem (2-Carbomethoxyaminobenzimidazole) As Active Ingredient 
     The Abem active ingredient is dissolved in hydrochloric acid under heating, whereupon it is neutralized with an emulsion consisting of a mixture of ammonium hydroxide, paraffin oil and β-cyclodextrin. The suspension is stabilized with tensides in a manner known per se. The seed-treating agent has the following composition: 
     
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Abem                    15%                                               
Paraffin oil            19.8%                                             
β-cyclodextrin     5%                                                
Ethylene glycol         5.6%                                              
Ammonium chloride (formed on neutra-                                      
                        about 10%                                         
lizing the hydrochloric acid solu-                                        
tion)                                                                     
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     Various tensides: 
     
         ______________________________________                                    
Emulsogen M             0.24%                                             
Atlox 4868 B            1.6%                                              
Triton X 45             1.9%                                              
Tensiofix L 051         0.2%                                              
Tensiofix 821           0.2%                                              
filled up with water to 100%                                              
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