FUNGICIDES 



381 



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Figure 151. Toxicity of compounds of the elements toward conidia of Boirytis sp. 

 (cinerea type) in relation to the position of the elements in the periodic system. The 

 heights of the columns are the reciprocals of the LD50. Stippled elements were not 

 tested and I, Br, CI, F, and S can be assigned no definite value since the toxicity varies 

 with the degree of oxidation. 



Organic compounds. The organic compounds offer immense possibili- 

 ties as fungicides. While it would be unquestionably a great discovery to 

 find a "cure all" among the organic compounds, it appears more likely 

 that these compounds will be more specific in their action than the heavy 

 metals. 



In preliminary slide-germination tests of miscellaneous organic com- 

 pounds the thiocyanates and alkyl and acyl resorcinols were found to be 

 highly fungistatic, but formaldehyde in such tests was only mildly active.^' 



In cooperation mth Dr. R. H. Wellman,* an extensive investigation is 

 being made on organic compounds as fungicides. To date, some two thou- 

 sand organic or metallo-organic compounds have been tested by one or 

 more of the above methods. Many interesting results are being obtained. 

 Toxic compounds have been found among all classes studied. However, 

 there is a marked specificity in the action of the various compounds, some 

 being very toxic to certain fungi or diseases while other fungi or diseases 

 show great resistance to the toxic action. Organic compounds have been 

 found, the toxicity of which exceeds that of copper sulfate or Bordeaux 

 mixture — the standard fungicide. 



One of the most interesting and promising compounds is glyoxalidme or 

 imidazoline, HN— CH=N— CHa— CH2. A large number of the glyoxali- 



dine derivatives have been examined by one or another of the methods 

 mentioned above. In slide-germination tests maximum fungistatic action 

 was achieved with glyoxalidine having a straight-chain substituent con- 

 taming 13 to 17 carbon atoms in the 2-position, as illustrated in Fig. 152. 

 Substituents in the 1-position, such as hydroxyethyl, aminoethyl or butyl, 

 do not markedly affect fungistatic action. The action of the glyoxalidine 

 derivatives is fungistatic and not fungicidal; they are removed from solu- 

 tion by spores in amounts proportional to their fungistatic action. In 

 greenhouse experiments maximum phytotoxicity is reached with the 11 

 to 13 carbon atom side-chains in the 2-position. Thus the greatest spread 

 between fungistatic action and phytotoxicity, for the hydroxyethyl deriva- 



* Carbide and Carbon Chemicals Corporation and Crop Protection Institute. 



