34 MASS. EXPERIMENT STATION BULLETIN 352 



to each 100 feet of row were required to give a good protective covering. .Scotch 

 soot costs about $7 per 100 pounds, largely because it is imported, and at that 

 price it cannot be used economically on carrots. However, there is no apparent 

 reason why local soot would not be just as effective if it were available. In addi- 

 tion to repelling the carrot rust fly, the soot apparently caused a healthier growth 

 of the foliage and roots of the treated carrots. 



Miscellaneous. — Among the miscellaneous repellents, talc and wood ashes 

 gave good protection from very light infestations, but it was apparent that their 

 action was entirely mechanical and that they would not be effective on large 

 plantings against a severe infestation. In home gardens where they can be applied 

 very carefully, they offer a cheap material which will give considerable protection 

 against light infestations. Limestone was inconsistent, and kainit applied to the 

 seedbed just before planting injured the germination of the seed severely. 



SUMMARY 



The carrot rust Ay,Psila rosae Fab., which is considered the most destructive 

 member of the family Psilidae, was originally described from Bessarabia, Rumania, 

 in 1794. It was first found in North America in 1885 at Ottawa, Canada, and in 

 1893 it was identified at Pittsfield, Maine. It has now been reported from fifteen 

 states, principally in the northeastern and northwestern parts of this country, 

 and has not been found south of Adams and Fulton Counties, Pennsylvania, 

 which is approximately 40' north latitude. This insect was especially abundant 

 in 1928 and 1929 in the eastern United States and in 1936 and 1937 in Wash- 

 ington. 



Carrots, parsnips, celery, and parsley are most commonly damaged by this 

 insect, but it has attacked several other plants of the botanical family Umbellijerae 

 in Massachusetts. Long varieties of carrots are preferred to short, thick varieties, 

 and at Waltham the white varieties of stock carrots suffered more injury than the 

 long orange varieties. 



Damage is caused entirely by the feeding of the larvae on the fleshy roots. 

 In large carrots the larvae may be well distributed between the second and 

 eighth inch, but in short carrots 70 percent of the larvae are found in the second 

 and third inches. When carrot roots are about one fourth inch in diameter they 

 may be attacked by the larvae of the carrot rust fly, and normal, well-grown 

 carrots are more likely to be damaged than stunted, mature carrots. 



In 1929, 79 pupae per square foot of soil were found where infested carrots were 

 left over winter, and only 3.3 pupae per square foot where carrots were pulled in 

 the fall. In 1931 and 1932 the natural abundance had decreased to approximately 

 one tenth this number. 



The life stages of the insect are illustrated and described briefly. 



The carrot rust fly hibernates as a pupa in the soil. The majority of them are 

 within 6 inches of the surface but they may be 10 inches deep. Flies appear about 

 May 25 and more of them emerged on days when the temperature was 60° F. 

 or less than when it was higher. In laboratory studies a temperature of 65° F. and 

 a soil moisture of 25 percent saturation were most favorable for emergence. 

 Female flies are slightly more abundant than males^ although there may be a 

 greater proportion of males early in the emergence period. The flies are short- 

 lived, and in confinement lived 9 to 1 1 days at cool temperatures and 2.6 to 3.8 

 days at 85° F. 



Eggs are laid singly in or on the soil near the plant, and the number per female 

 has varied from a maximum of 35 to an average of 6 to 18 The greatest number 

 of eggs was laid at 55° to 65° F., and the principal oviposition period of flies of 

 the overwintering generation extended in three seasons from May 27 to June 3. 



