CABBAGE MAGGOT 233 



three weeks' duration. The larval skin hardens at the end of that 

 period, and the insect pupates either close to the stalk or two inches 

 away. This stage lasts about two weeks. The fly has two or more 

 broods (Figs. 240 and 241). 



It attacks the cabbage and cauliflower, also turnips and 

 radishes, but cauliflower is its preferred food. The maggot tun- 

 nels in the roots of the plants, causing those attacked (Fig. 242) 

 to wilt and usually to die. 



Control. Clean cultivation is helpful. Crop rotation is desir- 

 able. Cabbages and cauliflower in a breezy location are not so 



FIG. 242. A cabbage plant wilted down, as result of attacks of cabbage maggot. 



liable to suffer as those sheltered from the breeze. Plants hi sandy 

 soil appear to suffer most. Seed beds in cold frames invite attacks 

 of the fly, and young plants are often affected when transplanted; 

 cold frames containing the cabbage or cauliflower plants should 

 therefore be covered with screens in order to prevent the entrance 

 of the fly. Old cabbage or cauliflower stalks should not be per- 

 mitted to remain in the field over winter. Tarred paper disks are 

 in some localities placed around the crown of the plant when it is 

 set out, but these are not always practicable or effective (Fig. 

 243). Since the adult flies are, like the house-fly, attracted to 

 sweet substances, recent experiments indicate that plants may be 

 sprayed with a sweetened poisoned liquid, thus destroying them 



