34 



which also attacks it has failed to accomplish much. Thus far, 

 in this country, treatment by man has proved necessary, these 

 natural enemies failing to do more than merely hold the insect 

 slightly in check. 



Treatment. 

 Many methods of treatment for the scale have been tested and 

 a number have proved to be of more or less value. The great 

 difficulty in treating infested plants with sprays is that, as the in- 



CL 



Fig. 2. — San Jose scale on pear: a, natural size; 6, much enlarged. (Howard, Circ. 3, 

 2d. ser., Div. of Eat., Dept. of Agr.) 



sect obtains its food from the juices of the plant, no arsenical 

 poison is of the slightest use, and it must be killed by something 

 which touches it. This is extremely difficult, both because the 

 insect is so small, even when full grown, and because the scale 

 over it is very hard and resistant. The only time at which the 

 insect can be reached with mild sprays, such as kerosene emulsion, 

 is when it is crawling and before it has formed a scale. But new 

 young are constantly appearing from about the fifteenth of June 

 till late in the fall, so that if this method were adopted, spraying 

 "would have to be repeated every week during at least four months. 



