1907.] The Cottony Maple Scale in Illinois. 



351 



work showed that a 15 per cent, emulsion was injurious to the tree, 

 taking nearly all the leaves from the box-elders and the lindens, and 

 half those from the soft maples. In this same year ( 1904) Mr. S. A. 

 Johnson, of the Col. Agricultural Experiment Station, made a num- 

 ber of laboratory experiments with the summer treatment of this 

 insect, reaching the conclusion that after the young are a week or 

 ten days old they are not easily killed by the kerosene emulsion, but 

 that before reaching this age they may be effectively treated by 

 sprays of as low a strength as 5 per cent. 



The following year (1905) Dr. J. W. Folsom, of the University 

 of Illinois, made for me a series of experiments, opportunity for 

 which was provided by the courtesy of Mr. O. C. Simonds, Super- 

 intendent of Graceland Cemetery. 



A 10 per cent, emulsion of kerosend was applied to several trees 

 of medium size with the use of a Bordeaux nozzle on an extension- 

 pole. A solid stream was first directed against the egg-masses in order 

 to loosen and soak them, after which a very fine spray was applied 

 as thoroughly as possible to both sides of the leaves. A solution of 

 whale-oil soap (one pound to six gallons of water) was applied to 

 an eighth tree by the same apparatus and with the same care. 



The effect of the spray was tested by counting both dead and 

 living scales on twenty-five leaves picked at random from different 

 parts of each tree, one series of counts being made just before the 

 spray was applied and another as soon as possible after it had dried 

 away and taken effect. Among the trees receiving the 10 per cent, 

 emulsion of kerosene were one tree sprayed July 3, at the beginning 

 of the hatching period of the scale, one treated July 11, at about 

 the middle of this period, three treated July 19 and 20, at the end 

 of the period, and one treated twice, once at the middle and once at 

 the end. The tree receiving the soap solution was sprayed July 19 — 

 that is, at the end of the hatching season. 



Four hundred and eighty-four thousand scales, borne by four 

 hundred and fifty leaves from these various trees, were critically 

 examined, and classified as either living or dead. The ratio of bene- 

 fit — the percentage, that is, of scales actually killed by the spray — 

 was determined in all cases by eliminating from the calculation the 

 scales dead at the beginning of the experiment, and figuring the per- 

 centages only on the number of scales alive when the spray was ap- 

 plied. The following table gives the essential data and results of 

 these experiments. 



