430 BOARD OF AGRICULTURE. [Pub. Doc. 



The results of this experiment cannot now be determined, as 

 sufficient time has not yet elapsed. 



Several parasites are also known, but they have not thus 

 far shown their ability to control the scale ; and a fungous 

 disease Avhich also attacks it has failed to accom})Hsh nuich. 

 Thus far, in this countr}^ 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 insect 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 extremel}^ difficult, 

 both because the insect is so small even Avhen 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 younof are con- 

 stantly 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 ever>^ week during at least four 

 months. It is therefore prefemble to use stronger insecti- 

 cides while the trees are dormant in winter, and the best 

 results are obtained by spraying in February and March, 

 and even later, till the buds begin to open. 



Fumigatioi} . 



For small trees, which it is possible to cover with an air- 

 tight tent, fumigation is the most reliable treatment which 

 can be used, as the gas will reach all the insects when a spray 

 would probably fiiil to do this ; but the cost of a tent increases 

 so rapidly with its size that only small trees can profitably 

 be treated in this way. In the case of nursery stock, how- 

 ever, this is the best treatment to make use of. Certain 

 cases have been reported in Avhich destruction of the scale by 

 fumigation has apparently not been a success. In every 



