l68 MINNESOTA STATE HORTICULTURAL SOCIETY. 



SPRAYING MATERIALS. 



PROF. HARRY SNYDER, ST. ANTHONY PARK. 



It is a frequent experience that the use of the same kind and 

 amount of a spraying material does not always give the same re- 

 sults, and sometimes, too, there is injury attending the application 

 of an insecticide or a fungicide as great as would have been the 

 damage from the ravages of the insects which the sprayer has sought 

 to destroy. If one seeks the cause of the difficulty, he will find 

 that there is a difiference in the chemical composition and purity of 

 the different spraying materials, as Paris green, London purple and 

 hellebore, and also that there is a difference in the action of these 

 fungicides even when they are apparently of the same degree of 

 purity. In the case of Paris green, most of that on the market con- 

 tains less than fifty percent of arsenic and twenty-five percent of 

 copper. A good green should contain fifty-six to fifty-eight percent 

 of arsenic and twenty-nine to thirty percent of copper. 



The difficulty with many Paris greens that causes burning of the 

 foliage is not adulteration as much as poor methods of manufacture, 

 resulting in the leaving of a large amount of soluble arsenic in 

 the green. When Paris green is properly made, practically all of 

 the arsenic is chemically united with the copper, so as to be in- 

 soluble and to remain on the surface of the leaf. It is the soluble 

 arsenic that is absorbed by the tissues of the plant which causes 

 the destruction of the foliage. In some Paris greens as high as 

 ten percent of soluble arsenic is present. If a green contains much 

 over four percent of soluble arsenic, it will cause the scorching of 

 foliage. Some greens are so poorly made that after they have 

 been applied and come in contact with the plant leaves the arsenic 

 is changed to a soluble condition. 



The only remedy that can be suggested is inspection by the 

 state of all insecticides and fungicides offered for sale. This is 

 done in a number of states, notably California and New York, and 

 the quality of the greens offered for sale in these states has gradu- 

 ally improved. 



Loss from scorching of the foliage caused by soluble arsenic 

 can in part be prevented by the use of an equal amount of slaked 

 lime with the green. In many cases the presence of the lime will 

 prevent the arsenic from going into solution and causing injury. 



The joint use of Bordeaux mixture and Paris green is meeting 

 with favor by many horticulturists. The Bordeaux mixture is pre- 

 pared in the usual way, by dissolving six pounds of copper sul- 



