13 



1. Complete or partial neutralization of the beneficial qualities of one 

 or more. 



2. Liberation of some harmful element. 



Such substances are said to be incompatible. It should not be under- 

 stood, however, that chemical combinations between fungicides and in- 

 secticides are always harmful or undesirable. Sometimes the reaction is 

 known to increase rather than decrease the fungicidal value; in other 

 combinations the substances have no effect on each other. 



The diagram opposite page 13 shows the mixtures which may be made 

 with safety as well as those which should be avoided. 



In recent years there have come into commerce a number of proprietary 

 articles combining an insecticide with a fungicide. Typically the fungi- 

 cide is represented by a copper compound, while the insecticide is arsenic 

 usually in the form of lead arsenate. The tendency of manufacturers has 

 been to recommend a dilution of their product to a copper content lower 

 than that of a 4-4-50 Bordeaux. Within recent years, however, they 

 have increased the amount of copper and recommended a more concen- 

 trated application. The percentage of arsenic has approached more 

 nearly to the amount recommended by economic entomologists. Even 

 to-day, however, when the purchaser has mixed in a spray tank enough 

 of a low copper preparation to conform to the standard, he will have the 

 arsenic in great excess of the amomit needed. 



As an aid to the purchaser in making dilutions and in estimating the 

 value of a preparation. Table II shows the guaranteed arsenic content 

 and the amount of material required to furnish arsenic equivalent to the 

 standard formula. 



