THE CARROT RUST FLY 23 



year of extremely severe and widespread damage by the carrot rust fly. Nat- 

 urally, the planting of the same crop or one of the other host crops on the same 

 land year after year would encourage the continuance of rust fly infestations 

 and should be avoided 



Carrot rust flies are comparatively strong fliers and apparently are able to locate 

 host plants at a considerable distance from their point of emergence. Under such 

 conditions, however, the infestation is seldom severe, especially on early host 

 crops. At Waltham in 1928 carrots planted approximately 300 yards from pre- 

 viously infested plantings showed 32 percent commercial injury, while those 

 grown on land having heavily infested carrots the previous season showed 74.8 

 percent commercial injury. 



Rotation of these crops is a commendable practice from the standpoint of 

 disease prevention and general cuFture; and if infestation by the carrot rust fly is 

 suspected, carrots, celer\', or parsnips should be planted as far from the planting 

 of the previous season as practical. 



Carrots and celery are frequently grown as both early and late crops. Two 

 crops in a season provide ideal conditions for both the first and second generations 

 of the rust fly, and less injury from this insect will result if these crops are grown 

 only in early plantings or only in late plantings. It is better to omit the early 

 plantings and thus prevent the first generation of the pest from finding suitable 

 breeding quarters in which to build up a strong second generation. In Mass- 

 achusetts, late crops can be grown from seed planted June 15, and this will 

 completely avoid the flies of the first generation. 



As noted in the "Date of Planting'* studies, little or no injury by first generation 

 rust fly occurs when the seed is sown June 1 or later, and by planting an early 

 maturing variety (65 to 70 days) satisfactory bunching carrots can usually be 

 grown between the periods of attack by the first and second generation of this 

 pest. 



Harvesting 



Infested carrots should be pulled completely and thoroughly, including all the 

 stunted and otherwise worthless roots. The value of this is well shown in Table 5, 

 where it is reported that the number of carrot rust fly pupae recovered in the 

 spring was from 26 to 80 times larger where infested carrots remained in the 

 ground over winter than where infested carrots were carefully pulled and taken 

 from the field. 



Although the maggots and pupae of the carrot rust fly are less afi^ected by culti- 

 vation than are many insects, the movement of the soil crushes, buries, and 

 exposes enough of them to make fall plowing a recommended practice for infested 

 plantings. 



Storage 



Carrots infested with the rust fly maggots should never be stored, because 

 these maggots are able to continue their feeding and growth at ordinary storage 

 temperature. Even after careful grading, it has been found that many carrots 

 which were apparently in good condition when placed in storage were worthless 

 when removed, because of feeding by the rust fl\' maggots which had not been 

 discovered during the grading. 



The writer has not considered the fumigation of carrots infested with rust 

 fly maggots to be practical under general conditions; but if it is advisable for any 

 reason, the use of carbon disulfide at the rate of 4 ounces for each 100 cubic feet 

 for 18 hours is recommended. 



