59 
COMPARATIVE EXPERIMENTS WITH VARIOUS INSEC- 
TICIDES FOR THE SAN JOSE SCALE. 
In my Eleventh Report as State Entomologist, published in 
1903, 1 gave the results of experiments and extensive practical opera- 
tions with several of the more prominent insecticides used against the 
San Jose scale,* including whale-oil soap solution, hydrocyanic acid 
gas, kerosene emulsion, mechanical mixtures of kerosene, and lime 
and sulphur compounds known as the "California wash" when made 
with the addition of salt, and the "Oregon wash" when made 
with blue vitriol. All these substances have been found effective 
against the San Jose scale, but the kerosene mixtures and emulsions 
were abandoned by me in December, 1901, because of serious dam- 
age done to trees with these insecticides in 1900 by one of my spray- 
ing parties, working under the immediate personal charge of my 
most experienced operator.f Crude petroleum, much used in some 
other states, has been little used at any time in Illinois, and observa- 
tions made by one of my assistants in 1902 in the Catawba Island 
district in northern Ohio, where it had been extensively applied by 
orchardists, were so discouraging that I have made but a single ex- 
periment with it.:|: I i 
After the passage of the Illinois inspection law in 1899 ^^ ^^~ 
came my duty to treat, free of expense to the owner, all orchards in- 
fested by the San Jose scale which there was good reason to believe 
had become so infested before the passage of that act. As it has 
now become virtually impossible to trace existing infestations to so 
remote a beginning, this feature of our law has become practically 
inoperative, and the owner is required to treat infested trees on his 
own account. This fact has made it important that every effort 
should be made to distinguish, among the various available insecti- 
cides, those which are at the same time effective, cheap, and conve- 
nient of preparation and application, especially as several commercial 
compounds of lime and sulphur, and others with a kerosene basis, 
are being extensively advertised and offered in condition for immedi- 
*Twenty-second Rep. State Ent. 111., pp. 56-57. 89-90; Bull. 80, 111. Agr. Exper. Sta- 
tion, pp. 492-493. 
tTwenty-second Rep. State Ent. pp. 48-50. 
ilbid., pp. 93-95. 
243 
