1912'] The Gloomy Scale 89 



sprayed with the ordinary lime-sulphur, due perhaps to the 

 fungicidal action of the lime-sulphur killing out the winter form 

 of the red headed fungus, a rather common fungus disease of 

 this insect. 



The following winter we tried an extensive series of experi- 

 ments with all of the manufactured insecticides at our com- 

 mand. These insecticides may be divided roughly into two 

 classes, — the lime-sulphurs and the soluable oils. The lime- 

 sulphurs are highly concentrated mixtures of various compounds 

 of lime and sulphur, which are diluted with water to make 

 mixtures of various strengths for different plants and for differ- 

 ent seasons of the year. The soluable oils are essentially the 

 heavier oils of the petroleum series together with a vegetable 

 oil. When mixed with water they make a beautiful emulsion 

 that may be used for spraying with perfect safety. The very 

 day that the mixtures were applied it was evident that the 

 lime-sulphurs would not be as effective as the soluable oils. The 

 former dried on the bark in a very short time, while the latter 

 remained moist for several hours. Thus the soluable oils were 

 enabled to creep in around and under the thick closely-applied 

 dorsal scale and suffocate the insect. While the lime-sulphurs 

 were not able to penetrate the thick dorsal scale, and they dried 

 so quickly that they could not creep under, so that they killed 

 very few insects. 



Examinations of the sprayed trees every three or four months 

 until last fall showed that all of the soluable oils had been 

 effective, killing at least 95 per cent, of the scale, while none of 

 the lime-sulphurs had killed over 75 per cent. This represents 

 the difference between an effective and a non-effective spray 

 mixture. 



Another point that has been brought out in the course of our 

 investigations is the fact that the soft maples, red and silver, 

 are injured more by this insect than the hard maples like the 

 sugar and Norway. Careful inspection usually shows as high 

 as 90 per cent of the soft maples infested, whereas it is very 

 unusual to find as high as one per cent, of the hard maples in- 

 fested. In this connection the following host plant list shows 



