MARKET DISEASES OF FRUITS AND VEGETABLES 15 



of the topped bulbs or through wounds made elsewhere on the bulbs. 

 These lesions are semiwatery at first, becoming papery as they dry. 

 The color of the lesion is the most characteristic symptom. The fungus 

 appears to secrete a pigment that diffuses through the tissues in 

 advance of the hyphae. These tissues are yellow at first, later becoming 

 red, then brown, and finally almost black as the dark-colored hyphae 

 fill the older parts of the lesions (pi. 5, Z>, E). Sometimes only one 

 or two outer scales are affected whereas at other times the entire bulb 

 may be destroyed, especially in the case of winter bottom sets. 



CAUSAL FACTORS 



The causal organism develops most rapidly between 72° and 86° F. 

 7ery little growth takes place above 93° or below 50°. At tempera- 

 tures of 70° to 72°, bulbs may be completely rotted in about 2 weeks. 



CONTROL MEASURES 



In regions where this disease is likely to become important, con- 

 trol may be effected by thorough and rapid curing and drying of the 

 bulbs after harvest. Onions should be stored in a dry, well-ventilated 

 house at temperatures between 33° and 36° F. 



(See 3, 9, 38, U.) 



SMUDGE (ANTHRACNOSE) OF ONIONS 



(Colletotrichum circinans (Berk.) Vogl.) 



OCCURRENCE, SYMPTOMS, AND EFFECTS 



Smudge attacks the onion, garlic, and shallot. Although it occurs 

 in the field it does not reduce the yield. Its importance lies in the 

 fact that it attacks onions at harvesttime and blemishes the scales, thus 

 decreasing the quantity of marketable bulbs. The injuries caused 

 in the field increase in transit and storage, with this addition, that 

 under very moist conditions the fungus not only causes blemishes 

 but also leads to destruction of the scales with consequent shrinkage. 

 The disease also causes sprouting of sets in storage. 



Smudge is characterized by black blotches or aggregations of minute 

 black or dark-green dots on the outer scales (pi. 4, D, E % F) . Each 

 of these dots is a fruiting body (acervulus) in which are borne innu- 

 merable spores of the fungus. These dots often are in concentric 

 rings, though they may be grouped in other ways. In severe cases, 

 the smudgy spots are so extensive that the side of the onion appears 

 smoked. Usually the lesions are on the outer scales, but they may 

 appear on the inner ones as well. On fleshy scales the fungus pro- 

 duces sunken, yellowish spots that enlarge slowly. The disease rarely 

 occurs on yellow and red varieties and then only on the uncolored 

 portions of the outer scales at the neck of the bulb. The disease occurs 

 widely, but only white varieties are seriously affected. 



CAUSAL FACTORS 



The pathogen is the fungus Colletotrichwn circinans. It occurs 

 on onion scales in the soil or on bulbs and sets in storage, which carry 



