Cucumber Diseases 141 



Anthracnose 



Csaisedhy Colletoirichum lagenan'um (Pass.) Ell. 

 and Hals. 



Symptoms. This disease is often serious on green- 

 house cucumbers and muskmelons. It is seldom so 

 in the fall and winter, but is most frequently met 

 with in the spring of the year. Affected plants 

 dry up and present a parched appearance. The dis- 

 ease also attacks the cucumber leaves, forming round 

 spots (fig. 21, b.), and on the fruit, deep cank- 

 ers, thus ruining its market value. It is claimed by 

 practical greenhouse men that the great difference 

 in temperature between day and night, which is un- 

 avoidable in the spring when the fires have gone 

 out, favors infection. 



The Organism. In structure, Colletotrichum la- 

 genarium resembles the organism of bean anthrac- 

 nose. The cucumber fungus has a peculiar ability to 

 remain dormant during the dry weather; but it is 

 easily revived by moisture. The fruits of the fun- 

 gus are borne in masses on the pustules which take 

 on a salmon color. The spores are typical of all 

 CoUetotrichums — that is, oval, one-celled, and hya- 

 line. The setae in C lagenarium are not very plenti- 

 ful. In pure culture it resembles C. lindemuthia' 

 num; however, pathologically it is distinct from the 

 latter, since numerous attempts by the writer and 

 by others have failed to infect growing bean plants 

 with the watermelon anthracnose or the watermelon 

 with that of the bean. 



