20 



MASS. EXPERIMENT STATION BULLETIN 352 



Injury by the second generation has never been so definitely connected with 

 the date of planting as that by the first generation, but there is considerable 

 evidence to indicate that the later the carrot seed is planted the more likely 

 there is to be injury by the second generation larvae. This was especially noticeable 

 in the 1928 plantings when over 80 percent of the carrots planted in June were 

 commercially damaged (Figure 2). Records of second generation injury have 

 been taken from the middle of September to the first of October. At that time 

 early-planted carrots are old and hard, and it is apparent that the more tender 

 growth of late-planted carrots is more attractive to the flies. 



Table 18 summarizes the records of planting dates at Waltham from 1928 

 to 1932. Because of variable degrees of infestation during these years, the results 

 are not so consistent as in Figure 2 but the general trend is quite evident. 



Table 18. Effect of date of planting on infestation of carrots by 

 carrot rust fly 



Waltham, Mass. 1928-1932. 



Variety 



Date 

 Sown 



FIRST GENERATION INFESTATION 



SECOND GENERATION INFESTATION 



Number Number of Percentage Number Number of Percentage 



of Years Carrots of Carrots of Years Carrots of Carrots 



Observed Examined Commercially Observed Examined Commercially 

 Damaged Damaged 



Soil Moisture 



Infestations have been noticeably greater in cool, moist locations than in 

 warm, drv e.xposures. .Since 1930, when the infestations have been light, the ma- 

 jority of the infested carrots have been found only in the lowest parts of the field 

 where the soil has been moist and cool. 



Table 19. Effect of irrigation on the carrot rust fly 



Waltham, Mass. 1931-1932. 



PERCENTAGE OF CARROTS INFESTED 



Irrigated 



Not Irrigated 



None 

 None 



4.00 

 19.00 



