24 MASS. EXPERIMENT STATION BULLETIN 352 



A small experiment with fumigants, which is summarized in Table 23, was 

 made in October 1930, using 25 carrots having an approximate equal infestation 

 in each of the treatments. The carrots were fumigated in iron barrels having a 

 capacity of 3J^ cubic feet. No injury to the carrots was observed and the odor 

 of the chemicals disappeared quickly with airing. 



Table 23. Effect of fumigation on carrots infested with carrot rust 



FLY larvae 



Waltham, Mass. October, 1930. 



Exposure Number of Living 



Material Rate Hours Maggots Found 



Calcium cyanide 1 lb.-l,000 cu. ft. 18 1 



Paradichlorobenzene 12 oz.-lOO cu. ft. 42 



Carbon disulfide 4 oz.-lOO cu. ft. 18 



None 21 



Infested carrots which have been brought in from the field should be treated 

 so that the maggots are killed. This can be done by putting them into silage, 

 feeding to stock immediately, or storing for later disposal in an absolutely tight 

 container which can be washed out later with boiling water or strong disinfectant. 



INSECTICIDES 



Preliminary experiments in the laboratory showed that the eggs and adults 

 of the carrot rust fly were killed by several of the common insecticides, and the 

 practical use of these materials is primarily a matter of expense and thorough 

 application. With low yields and moderate prices, the use of insecticides to combat 

 the carrot rust fly might be questionable; but where yields of 500 bushels per 

 acre are obtained and in seasons when the infestation is so severe as to place a 

 price premium on uninfested carrots, the application of insecticides should be 

 worth while. In general, however, the writer agrees with Doran and Cuba (6) 

 that spraying is seldom practical because "a horse-drawn sprayer naturally cannot 

 be used in such a closely planted crop as carrots," and "a small compressed-air 

 sprayer lacks in both capacity and pressure." 



Laboratory Experiments 



Eggs 



In 1929 carrot rust fly eggs were placed on moist blotting paper in petri dishes 

 and carefully but thoroughly sprayed or dusted. The materials used were corrosive 

 sublimate solution 1-1,000, Derrisol spray 1-250, Bordeaux-oil emulsion 1 percent 

 oil, 4 percent calomel-lime dust, and undiluted ground derris root (5 percent rote- 

 none). No larvae hatched from eggs e.xposed to any of these treatments, while 

 about 20 percent hatched from the untreated eggs. 



Flics 



During 1928, 1929, and 1930, about 300 newly emerged carrot rust flies were 

 confined in groups of 10 in lantern globe cages over potted carrots which had been 

 sprayed or dusted with various insecticides. Where dusts were used, the flies 

 were confined with the treated plants immediately (Fig. 3) after application, except 

 in special experiments; but the liquid sprays were allowed to dry on the plants 

 before the flies were caged with them. 



