BLIGHT AND LEAF-SPOT OF CARROT IN 

 MASSACHUSETTS 



By W. L. Doran, Research Professor of Botany and E. F. Guba, Assistant 

 Research Professor of Botany* 



Blight and leaf-s})ot of carrots are not new in Massachusetts. In the very 

 rainy summer of 1920, these 'diseases were unusually conspicuous and conse- 

 quently there was a suddenly increased interest in them on the part of some 

 of the growers who wished to know whetlier or not it would be profitable to 

 attempt to protect carrots against them, and how. As a result, investigations 

 of their real economic importance, cause, and control were undertaken, ;ind 

 the results of these investigations are here presented. 



Economic Importance 



These diseases may cause loss by reducing the yield of carrots, or the pres- 

 ence of tlie fungi on the petioles of the leaves may so weaken them as to 

 make the pulling of the roots more difficult, with consequently increased cost 

 of harvesting. According to Clayton (1)^, the roots are more susceptible to 

 decay following an attack of carrot blight. 



The first crop of carrots is planted in Massachusetts as early as the soil 

 can be prepared, and is harvested when about half grown to be marketed 

 in bimches. Neither of these diseases has caused any appreciable loss on 

 early or bunch carrots in this state. However, according to Chupp (2), car- 

 rot blight in some sections of tlie country reduces the market \alue of carrots 

 sold in bunches by making tlie leaves unsightly. 



Tlie main crop oi carrots is planted later, that is, early in June, and \y. 

 liarvested about the last of October to be topped and stored for fall or winter 

 marketing. Blight and leaf-sjjot are generally present on late carrots and 

 it is usually on the late crop that they iia\e caused loss here. 



In Massachusetts, the economic importance of these diseases of carrots is 

 not great in the average season. In the rainy summer of 1922 wiien tiie dis- 

 eases were very conspicuous, the yield per acre at the Market Garden Field 

 Station in Lexington was only 11 per cent below the average. The diseases 

 are not important causes of lowered yields here except in summers of un- 

 usually heavy rainfall. 



Symptoms 



Leaf-spot and blight are often present together on the foliage, so tli.it from 

 the viewpoint of the market gardener they may constitute one disease. 



The leaf-spot disease nuiy occur at any point on the leaf although it is most 

 common on the margin. The spots are circular except when tiieir position on 

 the nuirgin of tlie leaves makes them .semicircular. The spots have a diameter 

 of 2 to 5 mm. (about iV to i\ inches), and they often coalesce to form larger 

 spots. The center of the spot is grayish brown and is usually surrounded by a 

 narrow yellow or straw-colored zone. On the lower surface of the spots a 



■' The investigation hei-f reported wass carried throush the lirst season by W. S. 

 Krout, formerly Assistant Research Professor of Botany. 



'.Numbers in parentheses refer to "Literature cited'', p. '278. 



