INJURIOUS TO CABBAGE AND RELATED CROPS 33 



cabbage plants in the field. It is (iiiite probable that farther 

 south a greater number of the flies hibernate. 



Control. 



The means employed for the control of the cabbage maggot 

 vary greatly with the character of the crop infested. 



For early cabbage and cauliflower. — When infesting these 

 crops, the injury may be in great measure prevented by the 

 use of carbolic acid emulsion. For this purpose the stock 

 emulsion is diluted with thirty parts of water. About half a 

 teacupful of the emulsion should be poured around each plant 

 a day or two after transplanting. The application should be 

 repeated every week for a month. Apparently the carbolic 

 acid emulsion does not to any great extent deter the flies from 

 laying their eggs, but is effective in killing the eggs and recently 

 hatched maggots with which it comes in contact. This method 

 has been used to a considerable extent by commercial growers, 

 but has not on the whole been found so satisfactory as the use 

 of tarred paper cards. 



The value of the use of tarred paper cards to prevent maggot 

 attack on early cabbage and cauliflower was demonstrated many 

 years ago, but has not come into general use by commercial 

 growers. This method of protection is more effective and at the 

 same time less expensive than carbolic acid emulsion, and there 

 is also no danger of injuring the plants. The cards are made of 

 one-ply tarred felt roofing paper, and are cut in the form of a 

 hexagon 4J inches in diameter. From one angle a slit extends 

 to the center of the card and radiating from the center there are 

 four to eight short slits whereby the card can be made to fit 

 snugly around the stem of the plant (Fig. 30). The cards 

 should be applied as soon as the plants are set out. To be most 

 effective, the plants should be set on a ridge rather than in a 

 depression because in the latter case the cards are likely to be- 

 come covered with dirt. They cannot be used on short-stemmed 



