152 Report of State Board of Horticulture. 



calities where our insecticide work was in progress, and tiad, indeed, been 

 noticed and reported as early as 1898 by another assistant of the office, 

 Mr. E. B. Forbes, engaged in distributing to infested trees in southern 

 Illinois the spores of a fungus parasite of the San Jose scale. 



This spontaneous death of many of the scales which might have been 

 expected to pass the winter alive, was apparently due in great measure 

 and in both instances to a severe drouth of the preceding year. Con- 

 sistently with this explanation the dead scales were most abundant on 

 trees worst affected by the drouth, and on parts of trees to which the 

 flow of sap would naturally be least. 



Another observation of importance to the investigator was made with 

 reference to the action of the insecticide in loosening the scales of the 

 insects killed by it. In most cases where the application took fatal effect 

 the scales were so far loosened from the bark that they were easily rubbed 

 off, and might be washed away in large numbers by an ordinary rain. 

 As a consequence, if counts were made of dead and living scales upon a 

 tree before treatment, and again after a treatment and after a heavy 

 rain had fallen, the ratio of living to dead might be as great in the latter 

 case as in the former. It will be seen that by overlooking this circum- 

 stance an investigator might easily be led to very erroneous conclusions 

 as to the effects of moisture on the insecticide. 



GENERAL FEATURES OF THE EXPERIMENTS. 



The actual effect of rains was experimentally ascertained by heavily 

 spraying the trees with water at selected intervals after treatment with 

 the wash, and by making careful counts of dead and living scales in 

 each case and comparing the ratios so arrived at with those found in the 

 beginning. The trees sprayed with each mixture were treated exactly 

 alike except as to the subsequent application of water, and in this latter 

 respect the different trees received very different treatment. Some, for 

 example, were watered but once, and that the next day after the applica- 

 tion of the insecticide wash; and others were watered daily for the 

 seven days next following it. In order to avoid interference with the 

 experiments by rains, which fell three times during the fortnight covered 

 by the greater part of the experiments, some of the trees were covered 

 by canvas tents at night and whenever rain threatened. 



GENERAL STATEMENT OF RESULTS. 



Details of all forms and variations of the experiments will be given fur- 

 ther on, but it is sufficient for this general statement to say that the 

 general average result of a single spraying of twenty trees with lime, sul- 

 phur, and salt was the destruction of ninety and six-tenths per cent of the 

 scales when no water was applied within five days and of eighty-six per 

 cent when water was used. The corresponding result of the application 

 of lime, sulphur, and blue vitriol to fifteen trees was the destruction of 

 ninety-three per cent of the scales without water, and ninety-two and 

 two-tenths per cent when water was applied within the first five days. 



