10 BULLETIN 727, U. S. DEPARTMENT OF AGRICULTURE. 



$500. At Live Oak, Fla., there was a report of a total loss of the 

 crop on one 15-acre field in 1916 due to this disease. 



To summarize, it is evident that this disease under certain con- 

 ditions becomes epiphytotic and causes serious losses, especially 

 among watermelons and coldframe cucumbers. On the pickle crop 

 it is of less importance. Anthracnose seems to be primarily a dis- 

 ease of large fields rather than small gardens, a disease which, as a 

 rule, becomes a serious factor only where its hosts are grown in exten- 

 sive ' ' pure culture. ' 



DESCRIPTION. 



The symptoms of this disease vary somewhat with the different 

 hosts. All parts of the host plant are subject to attack. Lesions 

 tend to increase continuously in size. Acervuli are formed in 

 abundance. 



On cucumber leaves the lesions usually first appear on a vein and 

 become angular or amoeboid in shape, owing to the more rapid 

 development and consequent rhizoid extension along the veins. The 

 lesion consists of reddish brown, dry, dead tissue, often surrounded in 

 its earlier stages by a narrow, yellowish, translucent or water-soaked 

 border (PI. I, A). Inconspicuous acervuli are produced along the 

 veins on the upper epidermis of the brown center. Larger lesions 

 become more circular and blotchlike (PI. II, B). The dead centers 

 crack transversely and may be beaten out by rain. Leaves being 

 killed by the coalescence of a few large lesions become ragged in 

 appearance (PI. II, B). Very numerous incipient lesions may cause 

 the sudden blighting of leaves. On young rapidly growing leaves 

 small lesions may cause crinkling and extreme distortion. 



Cucumber petiole and stem lesions are linear to narrowly oval, 

 first slightly sunken and water-soaked or yellowish. Numerous 

 acervuli are formed. The surface of such lesions later becomes quite 

 dry and chalky in appearance (PI. I, B). Cucumber stem lesions 

 tend to remain shallow and superficial, and the collapse of mature 

 stems at diseased points is uncommon. 



Cucumber fruit lesions appear first as more or less circular, sunken, 

 water-soaked areas. Sporulation is abundant. The surface of such 

 lesions becomes buff or pinkish in color, later turning to black. On 

 mature fruits the black lesions may show white central areas bear- 

 ing the old acervuli as conspicuous black dots. A dry rot is usually 

 produced in the underlying tissue and the sunken epidermis may 

 crack, exposing a cavity underneath. 



In the field, anthracnose of cucumbers is characterized by the 

 parched or scorched appearance and spotting of the leaves. The 

 chief damage is due to the destruction of the leaf laminae. Stem 

 and petiole attack is not very evident and fruit injury is conspicu- 

 ous only in the seed crop. 



