SUPPLEMENTS FOR COPPER FUNGICIDES 



By E. B. Holland, Research Professor of Chemistry, and C. O. Dunbar and 

 G. M. Gilligan, Research Assistants in Chemistry' 



Introduction 



Ever since copper fungicides were introduced, numerous supplementary 

 products have been recommended for incorporation in the spray with a 

 view to remedying some real or fancied defect. This a])plies particularly to 

 Bordeaux mixture but also to Burgundy and the acetates. In many cases the 

 reputed defects were due probably to faulty methods of preparation or 

 of application, although in some instances the claims were well founded 

 and deserve attention. Most of these shortcomings have been enumerated 

 by different investigators in some form or other and various treatments 

 suggested for their amelioration, of which the following are the most 

 important: 



1. To increase the activity of the fungicide by increasing the concen- 

 tration of the copper ions. 



2. To increase suspension by deflocculating the fungicide, by increas- 

 ing the viscosity of the dispersion medium, or both. 



3. To increase wetting power by reducing the interfacial tension at 

 the leaf-spray interface and thereby facilitate spreading and distribution. 



4.. To increase adhesiveness by foriinng more resistant deposits. 



5. To prevent or reduce crystallization or decomposition by the addi- 

 tion of protectors. 



6. To prevent or reduce interactions between fungicides and insecti- 

 cides in combined sprays. 



7. To increase visibility of the deposit. 



As a rule supplementary products are added for a specific purpose, but 

 their influence is manifested generally in more than one direction due to 

 the interdependence of the various attributes of a spray. Space does not 

 permit an adequate review of the literature on the subject but attention 

 is called to some of the earlier investigations. 



1. To increase the activity of the fungicide by increasing the concentration 



of the copper ions. 



The toxicity of a salt in solution is equal to the combined toxicity of its 

 base and acid or, according to Kahlenberg and True (47)" for the various 

 copper salts, to the combined action of its ions; but Coupin (18), Clark 

 (16, p. 37, 40) and Pickering (3, p. 127) have shown that in dilute solu- 

 tions the action of the acid radical is negligible, although Bain (1, p. 27, 

 28) noted some exceptions. Pfetfer (73, p. 273, 274) claims that the 

 physiological action of poisons increases with the degree of ionization 

 although undissociated portions may be active, and that non-electrolytes 

 are also poisonous and may imdergo chemical decomposition in a way 



^With the cooperation of Dr. E. P. Guba. Assistant Research Professor of Botany. 

 -Reference is made by number to Literature Cited p. 108. 



