THE CABBAGE MAGGOT 27 



In the last fourteen years at Waltham, 78.7 percent of the untreated cabbage 

 plants have been commercially injured, and the natural infestation has been 

 less than 75 percent in only three of these years. 



The recommended seedbed treatments to prevent loss from this pest are to 

 cover the bed with cheesecloth, or to apply corrosive sublimate solution 1-1920 

 at the rate of 1 gallon to 40 feet of row three or four times at weekly intervals 

 while the flies are laying eggs. 



Pre-transplanting treatments applied by coating the lower stem and roots with 

 calomel-talc equal parts, or calomel 1 part and talc 3 parts, have been effective 

 and are recommended on plants which are transplanted with bare roots. Dipping 

 these plants in a calomel-water suspension containing various adhesives was un- 

 satisfactory. 



Field treatments for cabbage maggot control are divided into repellents, toxic 

 dusts, and toxic liquid drenches. 



Among the repellents, tar paper discs gave excellent control when carefully 

 applied, and are recommended for use in home gardens especially. Mulch paper 

 increased plant growth 17 to 32 percent but provided poor protection and is not 

 considered practical for cabbage maggot control. 



Among the insecticidal dusts, naphthalene flakes were effective if the applica- 

 tion was repeated frequently, but they are not advised for large-scale treatments. 

 Rotenone dusts were not satisfactory as used. Calomel-talc dust, 4 percent 

 calomel, applied by the duster method was moderately effective and satisfactory 

 if the infestation was light. When this dust was applied by the mound method, 

 it was one of the best treatments used. 



Liquid drenches of calomel-gum suspension and Semesan gave satisfactory 

 control but are expensive and the former is difficult to prepare. Corrosive sub- 

 limate solution, prepared by dissolving corrosive sublimate powder, crystals, 

 or tablets in w^ater, is the standard material for combating the cabbage maggot. 

 The most effective solution contains 1 ounce of the chemical in 10 gallons of 

 water, a dilution of 1-1280, but experiments have shown that a 1-1920 dilution 

 is satisfactory if carefully applied. Two applications, at the rate of one-half 

 cupful per plant, at weekly intervals, are advisable if the infestation is heavy; 

 but one application is often sufficient to control a light infestation. The first 

 application should be made within a week after the first eggs are laid, and more 

 than two timely applications are unnecessary. The solution is applied with a 

 bucket and dipper, a watering pot, and various mechanical devices. An especially 

 designed applicator was used successfully at Waltham. 



Experiments in 1942 and 1943, with reduced dosages which would conserve 

 material during the war emergency, indicate that corrosive sublimate solution 

 1-1920 and calomel-talc dust, 2 percent calomel, applied by the mound method 

 are effective if the application is made carefully. Calomel-talc dust, 2 percent 

 calomel, applied by the duster method was not effective, and corrosive sublimate 

 solution 1-2560 permitted a large increase in the number of slightly injured 

 plants. 



The cost and practical value of the recommended treatments are discussed 

 and summarized in Table 13. 



An effective control of the cabbage maggot in radishes was not discovered, but 

 relatively small losses occurred if the seed was planted between May 25 and 

 June 5, or after July 10. 



