44 MISC. PUBLICATION 440, U. S. DEPARTMENT OF AGRICULTURE 



the velvety grayish-brown appearance of the abundant fruiting stalks 

 and spore masses. Infection normally occurs through wounds. 



Temperature studies have shown that the gray mold pathogen can 

 infect carrots throughout a range extending from 32° F. to approxi- 

 mately 76°. Decay was greatest at 72.5°. The percentage of infec- 

 tion and the rate of decay were considerablv reduced bv storage at 

 temperatures of 32° to 35.6°. (See also Peas. Gray Mold Rot, p. 37). 



MACROSPORIUM LEAF BLIGHT 

 (Macrosporium carotae Ell. and A. B. Langlois) 



Macrosporium leaf blight is rather generally distributed through- 

 out the commercial carrot-growing sections of the country. Frequently 

 it is of considerable economic importance in the field. On the market 

 it is occasionally found as a leaf blemish of bunched carrots. The 

 disease is confined to the leaves and is more severe on the older ones. 

 The symptoms are a yellowing and browning of the tissues in areas 

 of irregular size and shape at the margins of the leaf. Entire leaves 

 may turn yellow, brown, and finally black, without the formation of 

 individual scattered spots. Where the disease is widespread in the 

 field the blighted foliage is very conspicuous. During seasons when 

 blight is of importance, increased yields may be obtained by spraying 

 with bordeaux mixture. 



(See 163, 169.) 



RHIZOCTONIA CROWN ROT 



(RMzocionia solani Kiihn ; Corticium vagum Berk, and Curt.) 



Rhizoctonia crown rot is occasionally found on carrots both in 

 the field and in storage. As indicated by the name, the decay occurs 

 at the crown of the plant. There the leaf petioles (particularly of 

 the central leaves) are rotted off at the base and the leaves are killed. 

 The decay may then advance into the root. The affected tissues of 

 the root are brown and soft. The brown mycelium and chocolate- 

 brown irregular sclerotia of the fungus may be present on the surface 

 of decaying roots. 



An unusual set of symptoms was once observed on New York 

 carrots 10 held in cold storage throughout the winter. In addition 

 to the usual symptoms of decay at the crown there were numerous 

 small slightly depressed spots over the surface of the roots. These 

 resembled, in a general way, the lesions of fusarium rot (p. 43). 

 Infection had apparently taken place first in the secondary roots, from 

 which the decay had advanced to the taproot and had continued to 

 develop during storage. 



This disease is ordinarily not sufficiently important to require 

 special control measures. Carrots from fields in which the disease 

 was serious may be expected to show decay later on in storage, so 

 they should be marketed as soon as practicable. 



(See 168,221.) 



"Ramsey, G. B. mabkbt pathology notes prom Chicago. U. s. Bur. Plant Indus., 

 Plant Dis. Rptr. 18: 40-41. 1934. [Mimeographed.] 



