THE CARROT RUST FLY 



19 



Date of Planting 



The most important of these cultural practices is to grow the carrots at a time 

 when they will be least subject to attack by the carrot rust fly. Nearly every 

 reference states that damage from this pest can be avoided or decreased by 

 planting the seed after the period of attack of the first generation, and harvesting 

 the crop before the period of attack of the second generation. Carrots generally 

 develop to marketable size in 68 to 80 days from seed, depending upon the variety; 

 but plantings at Waltham required a somewhat longer growing period. 



Figure 2 



RELATION OF DATE OF PLANTING TO 

 INFESTATION OF CARROTS BY THE CARROT 



RUST FLY. 



WALTHAM, MASS. 19 2a. 



MAY I 



MAY IS 



JUNE I JUNE IS 



DATE SEED SOWN 



1ST GENERATION INFESTATION 

 eND GENERATION INFESTATION 



In Figure 2, which summarizes the results in 1928 during a heavy infestation, 

 the effect of planting at different dates is brought out very clearly. In this plant- 

 ing every carrot examined from the May 1 planting was infested by larvae of the 

 first generation, while none of the carrots planted June 15 had been infested when 

 examined on July 28. In this year, the growing season was late and the first 

 planting was not possible until May 1. In 1929 and 1930, however, the season 

 permitted plantings on April 1 and 15, and although the infestation was lighter 

 'in these years, the April plantings were more heavily infested than the later 

 plantings. It is, therefore, apparent that the earlier the carrots are planted the 

 more likely they are to be infested by the first generation of the carrot rust fly. 

 This is explained by the fact that the larger seedlings during the oviposition period 

 of the flies are more attractive for egg laying, and that cool, damp weather, which 

 is favorable for development, is more likely to occur. 



