138 



INSECTS INJURIOUS TO VEGETABLES 



fore they have burrowed far into the heads. Other appHcations 

 should follow frequently, as required, and can be made with 

 safety until the heads are about half formed, and even later, as 

 the poison, under ordinary circumstances, disappears from the 

 plants two or three weeks after being applied. 



Bran mash is, according to the testimony of some, successful 

 against cabbage worms. It is prepared in the same manner as 

 for cutworms and grasshoppers. See page 55. 



Kerosene emulsion is not as efficient as arsenicals, because 



Fig. i,9.—Pteromalus puparum. Female. 

 Highly magnified. (Author's illustra- 

 tion, U. S. Dept. Agr.) 



Fig. 90-— Parasitized cabbage worm {Pontia 

 rapas). showing cocoon mass of Apanfeles 

 glomeratus below. (Author, U. S. Dept- 

 Agr.) 



it is necessary for this spray to come into direct contact with 



the "worms." 



Pyrethrum has the advantage of not being poisonous to 

 humans, but is said by some cabbage growers to discolor the 

 leaves, and if its use is not continued at frequent intervals the 

 "worms" recover. It is more expensive than remedies that have 

 been mentioned. 



Hot water at a temperature of about 130° F. does practically 

 no harm to plants and destroys all insects with which it comes 

 in contact. 



Clean cultivation and trap crops. — If united effort in clean 

 farming could be secured, together with the use of arsenicals, 

 the losses due to the ravages of this and other leaf-feeding 

 cabbage pests might be largely averted. The practice of leaving 



