16 MASS. EXPERIMENT STATION BULLETIN 412 



dust in four weekly applications in 1932 gave good protection to cabbage but 

 poor protection to cauliflower. In 1933 the derris dust was moderately effective 

 in protecting against a light infestation (57 percent) when applied from two sides 

 (Table 9), while the cube dust was unsatisfactory in three applications applied 

 either from one side or from two sides. Although the newer derris and cube 

 dusts containing .75 to 1.0 percent rotenone will undoubtedly give better pro- 

 tection than was obtained in the 1932 and 1933 experiments, it is not believed 

 that rotenone will be as efi"ective as mercury compounds for controlling the cab- 

 bage maggot. 



In 1938 a derris dust containing .6 percent rotenone was applied weekly to six 

 different plantings of radishes and no protection resulted from the treatment. 

 In fact, the commercial injury was 1.67 percent greater on the treated than on 

 the untreated radishes. 



Calomel 



Calomel dusts ha\e been recommended and used for combating the cabbage 

 maggot since about 1930, but growers have generally obtained variable results 

 because of the difficulty in applying sufficient material around the stem of the 

 plant under practical field conditions. In the experiments at Waltham, calomel 

 dusts have given satisfactory control when applied by the duster method if 

 accurately timed, and excellent control when applied by the mound method. 

 Only powdered calomel is suitable for making calomel dust, and granulated 

 calomel should not be used. 



Dust containing 4 percent calomel is standard for cabbage maggot control. 

 When used by the duster method, the 4 percent dust was definitely superior, but 

 when applied by the mound method, a 2 percent calomel dust was also satis- 

 factory. 



Duster Method of Application. — Preliminary trials indicated that a plunger 

 type hand duster was more desirable than a rotary fan type hand duster for use 

 on cabbage, and this type was, therefore, used in most of the experiments at 

 Waltham (Table 9). The dust discharged by one full stroke of the plunger was 

 applied to the soil around the stem of each plant. In several of the tests the dust 

 was applied from two sides of the plant; but, although the double application 

 was slightly more effective than the single application, the difference was so 

 small that the additional cost for labor and material was not warranted. 



All applications were made at weekly intervals beginning when the first eggs 

 were found. As shown in Table 10, one or more applications at this time were 

 effective when a light infestation developed on untreated plants. In seasons 

 when a heavy infestation developed, an application one week after the first 

 eggs were found was the most effective of the single applications, but one applica- 

 tion alone at any of the periods did not give satisfactory protection. Applica- 

 tions at both the first and second periods were the most effective, although this 

 is not borne out by the figures in Table 10. The writer recommends from experi- 

 ence three applications during the first three periods. It is obvious from Table 

 10 that applications beginning in the third or fourth period, that is, two or three 

 weeks after the first eggs are laid, do not give satisfactory protection. 



