FUNGICIDES 383 



tives as shown in Fig. 152, is when the substituent in the 2-position is 

 heptadecyl. Side-chain unsaturation increases phytotoxicity, as does in- 

 creasing length of chain in the 1-position. The glyoxahdine derivatives in 

 greenhouse tests were phytotoxic to tomatoes at concentrations which 

 would not control late blight. 



Three of the substituted glyoxalidines have been tested under varied field 

 conditions in several states for several years. Against late blight of potato, 

 they were not effective, thus confirming the greenhouse results. Fair control 

 of black spot of roses was obtained. However, against apple scab they gave 

 control equal to the standard sprays, but with less injury and better color 

 and finish to the fruit; for the control of cherry leaf spot defoliation, 2-hepta- 

 decylglyoxalidine has been found superior to all other fungicides tested. 



Past and Future 



When these fungicide studies were begun, it was believed that the cause 

 of better and more efficient fungicides could be best advanced if the nature 

 of the mechanism of fungicidal action were better understood for our impor- 

 tant fungicides. Therefore, attempts were made along this line wdth the 

 classical standards, sulfur and copper. This work has been substantiated, 

 at least in part, and others have pursued it further.'*- ^•'^^ It is believed 

 that this is still a good policy. With new and improved techniques and 

 fresh concepts resulting from an intensive study of the "simple" slide- 

 gesmination method, this basic work could be carried much further. Espe- 

 cially inviting now from this angle are the new organic groups, such as the 

 dithiocarbamates and glyoxahdine derivatives. 



In the realm of new techniques of evaluation, it is probable that the out- 

 standing disease, apple scab, should receive first consideration, so that a 

 relatively simple and inexpensive greenhouse method would be available 

 for handling many hundreds of new chemicals. Further studies on the 

 improvement and standardization of techniques for the seed treatments of 

 the staple crops of corn and cotton also seem indicated. It should not be 

 forgotten that not all uses of fungicides are agricultural. Industrial applica- 

 tions, such as wood preservation and the textile and plastic fields, offer 

 many new and interesting problems, as has been brought to our attention in 

 the latter case by pressing war questions. 



There is still room for improvement in the heavy-metal fungicides, 

 especially by the use of metals other than copper and of molecular combina- 

 tions of different metals. The organic compounds have opened up an 

 immense field of study for fungicides with countless attractive possibilities. 

 As yet only a beginning has been made. 



