76 PAPERS ON INSECTS AFFECTING VEGETABLES. 



EXPERIMENTS WITH INSECTICIDES. 



During the spring of 1912 the following experiments were conducted 

 at Rocky Ford, Colo. 



On April 8 several infested horse-radish plants were sprayed with 

 the folio whig mixture: 



Paris green pounds . . 2 



Whale-oil soap do 8 



Water gallons . . 100 



These plants were kept under close observation for several days, 

 but no dead larvae were found. 



On April 29 several infested horse-radish plants were sprayed with 

 the following mixture: 



Arsenate of lead pounds . . 10 



Whale-oil soap do 10 



Water gallons. . 100 



This experiment was likewise a failure and no larvae were killed. 



In these experiments the poisons were carefully and thoroughly 

 applied. The surface and underside of the leaves, and in fact all 

 portions of the plants above ground, were coated. This treatment, 

 however, failed to kill the ] arvae. This was due to the habit the 

 larvae have of resting and feeding under compact webs, where they 

 are completely protected from stomach poisons. 



RECOMMENDATIONS FOR CONTROL. 



The experiments indicate that this insect can not be controlled 

 with arsenicals. If artificial control measures should become neces- 

 sary, much could doubtless be accomplished by burning the dead 

 horse-radish leaves and petioles during the winter. After the dead 

 leaves are removed the surface of the soil about the roots of the plants 

 should be thoroughly stirred with a rake. This cultivation would 

 crush or bury the hibernating larvae which were resting in cracks in 



the soil. 



CONCLUSION. 



The investigation of this insect indicates that infestation is limited 

 to a few horse-radish plants in one garden at Rocky Ford, Colo. In 

 this garden the larvae have evidently been prevented from causing 

 much damage by a hymenopterous parasite, and at present no arti- 

 ficial control measures are necessary. 



ADDITIONAL COPIES of this publication 

 -^i- may be procured from the Superintend- 

 ent of Documents, Government Printing 

 Office, Washington, D. C, at 5 cents per copy 



