SUPPLEMENTS FOR COPPER FUNGICIDES 107 



5. To prevent or reduce crystallization or decomposition by the 

 addition of protectors. 



Bordeaux mixture on standing loses its gelatinous character, settles, 

 gradually acquires a purplish color, and the final, dense aggregates are 

 said to be sphaero crystals of undetermined composition. Burgundy nux- 

 ture undergoes a somewhat sinular change and is converted into malachite. 

 The incorijoration of properly prepared protective substances may serve to 

 prevent or, at least, retard crystallization and to preserve the highly dis- 

 l)ersed character of the precipitate with its high power of suspension, excel- 

 lent wetting and spreading properties and adhesiveness. The use of protec- 

 tors with coarser suspensions probably act in a like manner but to a lower 

 degree. Kelhofer (49) advised the addition of sugar to Bordeaux mixture 

 to prevent crystallization, Butler (7, 8, 9) found 0.03 per cent of sugar 

 effective, and Lutman (61) reported both sucrose and glucose efficient. The 

 practice has become fairly well recognized for Bordeaux mixtures that have 

 to be kept for several hours. Data on the subject are rather meager, as 

 most copper fungicides are applied immediately after preparation. 



6. To prevent or reduce interactions between fungicides and insecticides 



in combined sprays. 



Generalizations on interactions involving so diversified products as arc 

 employed in disease and insect control are of questionable value. Most 

 of the copper fungicides and of the stomach poison arsenicals in current use 

 are relatively insoluble and fairly stable, but more or less subject to 

 hydrolysis and readily decomposed by soluble compounds such as nicotine 

 sulfate, soluble sulfides, soaps, etc. As a rule the arsenicals require more 

 consideration than Bordeaux, Burgundy and other copper fungicides, as 

 soluble compounds of arsenous and arsenic acids are extremely toxic to. 

 foliage. Lime-sulfur should never be combined with copper fungicides; 

 but in the case of arsenicals, milk of lime, calcium caseinate and protec- 

 tive colloids in general may serve to retard objectionable reactions. The 

 order of mixing has been emphasized by Robinson (81) and others. Some 

 writers treat the subject as merely a matter of compatibles and non- 

 compatibles. 



7. To increase visibility of the deposit. 



Bordeaux mixtures containing an excess of lime (whitewash) probably 

 yield the most conspicuous deposits on the leaf surface covered of any 

 of the copper fungicides. Several of the supplementary products serve 

 to increase substantially the visibility of basic sulfate and similar fungi- 

 cides, of which Wilkinite and wheat flour proved excellent. 



Summary. 



L The efficiency of insoluble copper fungicides is dependent largely 

 on the degree of dispersion and other physical characteristics, as deter- 

 mined by suspension, which is undoubtedly the simplest and most practical 

 method of evaluation. Wetting, spreading and adhesiveness are so closely 

 correlated and interdependent that complete differentiation is impossible. 



