278 MASS. EXPERIMENT STATION BULLETIN 245 



Summary 



Blight of carrots, caused by Mucruxporium corotae, and leaf-spot of car- 

 rots, caused by Cercospora npii carottte, usually occur together in Massa- 

 cliusetts. Blight is the more inijiortant here. 



These diseases usually cause no measurable loss on carrots pulled young 

 to be nuirketed in bunches. On late carrots, they cause no appreciable loss 

 in yield in dry summers and niodcrale to heavy loss in yield ni rainy summers. 



Factors aifecting spore germination and infection are considered. In Mass- 

 achusetts, summer temperature is a less important factor influencing develop- 

 •>ient of these diseases than moisture. 



The oldest leaves of carrot have been found to he most susceptible to blight. 



It has been foimd that l)oth fimgi jiass the winter on dead leaves of carrots 

 in or on the soil. No evidence has l)een found tliat either of these fungi is 

 carried on the seeds of carrots. 



Both fxmgi are verj' susceptible to the fungicidal action of co])])er. Lab- 

 oratory and field experiments with fungicides are described. It is not rec- 

 onunended that carrots b*- generally sprajed in Massachusetts, but in rainy 

 summers when blight was severe increases in yield resulted from spraying 

 with Bordeaux mixture. 



The latest sowings of carrots are least affected l)y i)light l)ecause of the 

 relative resistance to infection of younger leaves, and unfavorable tempera- 

 tures prevailing late in the growth of the crop. 



Literature Cited 



1. Clayton, E. E. Carrot rot information. Market Growers' Jour. ;38: J"). 



1926. 



2. Chupp, Charles. Macros])orium leaf-blight of carrot, in Manual of vege- 



table-garden di.seases. New York. 192.5. 

 .'3. Pas.serini, Giovanni. Cercotiporu <ipii var. carotae Atti, R. Accademi dei 



Lincei. Anno 286. Memorie delhi Classe di Scienze Fisiche, Matemiche 



e Naturali. Serie -1, vol. 6, p. 169. 1889. 

 4. Ellis, J. B. and A. B. Langlois. Macros poriuin raroloe, in New .species 



of Louisiana fungi. Jour. Mycology 6: 3.5-37. 1890. 

 .5. Klotz, L. J. Studies on Michigan celery diseases, 2. A study of the early 



blight fungus, Cerospora apii Fres. Mich. Agr. Expt. Sta. Tech. Bui. 



63. 1923. 



6. Reddick, Donald and Errett Wallace. On a lal)oratory method of deter- 



mining the fungicidal value of a spray mixture or solution. Science 31. 

 798. 1910. 



7. Doran, William L. Laboratory studies of the toxicity of some sul])lnir 



fungicides. N. H. Agr. Expt. Sta. Tech. Bui. 19. 1.922. 



Publication of this document approved by the 

 Commission on Administration and Finance. 



4 M-10-28. No. 3638 



