270 THE MONTHLY BULLETIN. 



Arsenical-Contact Insecticide Combinations. 



Tobacco. So far as known, the various forms of tobacco prepara- 

 tions are compatible with the arsenicals, Paris green being a possible 

 exception. (See tobacco-Bordeaux.) 



Soaps. As previously noted in the discussion of arsenicals-lime- 

 sulfur, the arsenites and the acid lead arsenate are all unstable in the 

 presence of alkalies. The alkalies of soaps, therefore, prohibit their use 

 with the arsenicals, except with the neutral lead arsenate, which is not 

 affected by the alkali of the soap. 



Emulsions. The above remarks applying to soaps obviously may 

 also be applied to the soap emulsions, with the added danger that the 

 emulsion may be broken and injury result both from the soluble 

 arsenic and the separated oil. 



Contact Insecticide-Fungicide Combinations. 



Lime-sulfur-Bordeaux. This combination has been used with 

 some success for the control of apple scab, but with more or less injury 

 to the fruit. Definite classification must be deferred until more infor- 

 mation is available. 



This subject brings to mind a "hard nut to crack" that was sent 

 in to the Insecticide Laboratory in the form of a question by one of 

 the County Horticultural Commissioners. The lower limbs of certain 

 trees had been sprayed with Bordeaux mixture as a check asrainst the 

 brown rot, either just before, or just after spraying with lime-sulfur 

 for red spider. It was noted that if the two sprays were applied 

 within a week or so of each other, a brown deposit was formed on the 

 leaves and twigs where the two sprays came together. It was assumed 

 that the deposit was copper sulfid. Now the question was, whether 

 this reaction would lessen the efficiency, either of the fungicide or of 

 the insecticide. 



Questions of this sort are interesting from a chemical standpoint 

 and are of considerable practical moment. Accordingly, the literature 

 was looked over and a few experiments were made and the reply given 

 substantially as follows: "So far as known to the writer, this reaction 

 has not been studied from a chemical standpoint. To predict the 

 products of the combination with certainty seems out of the question 

 for mixtures of such complexity. It seems very probable, however, 

 that a sulfid of copper is one of the products. Under certain con- 

 ditions, free sulfur, thiosulfates and sulfates of both copper and cal- 

 cium would also be among the products. A few rough experiments 

 made in the laboratory indicate that variations in the preparations of 

 the two constituents made a great difference in the appearance of the 

 final product. No very definite statement is, therefore, ventured. 

 Various mixtures, loosely spoken of as "copper sulfids" have been made 

 and experimented with by different workers, and they all are said to 

 possess marked fungicidal value. 



"It would seem that the two sprayings under consideration would 

 lessen the value of the lime-sulfur by removing some of the sulfur to 

 form new compounds with copper, but that the new copper compounds 

 would be efficient fungicides." 



