ANTHRACNOSE OF CUCURBITS. 33 



occurred since that resulting from the heavy rains of the first week 

 in the month. The light showers of August 26 seemed to result in 

 very little new infection, due possibly to the low temperatures follow- 

 ing this rain. 



Infection was sufficiently distributed and abundant, however, to 

 serve as ample source for a general spread of the disease in fields 1 and 

 2 following the heavy rains of September 4 to 7. A general epiphy- 

 totic became evident on September 12 and 13, the lesions being more or 

 less of a uniform age. In field 1 the disease was not only prevalent in 

 practically all of the plats, but the cucurbit varieties and a series of 

 interplanted cucumber seedlings, all at the foot of the general slope of 

 the field, became generally diseased, quite evidently as a result of 

 surface-drainage infection. . While the frost of September 15 killed 

 the vines, anthracnose was prevalent on the remaining cucumber fruits 

 of all sizes, as well as upon the fruits of the susceptible cucurbit 

 varieties, and on these fruits the disease persisted and even spread 

 consistently during the remainder of the month. 



It is to be noted that the disease first appeared, as in 1915, near the 

 middle of July and that there were two periods of extensive spread 

 following the two periods of heavy rainfall. There also seems to be a 

 rather noticeable temperature correlation, since marked spread of the 

 disease did not result from the rains followed by excessively high or 

 rather low temperatures. Owing to the lateness of a killing frost, 

 the latter of the two periods of spread above mentioned developed 

 into a genuine epiphytotic, thus demonstrating the potential de- 

 structiveness of this disease. 



DEVELOPMENT IN 1917. 



Observations made during June, 1917, in the watermelon regions of 

 the South indicate that here again the weather plays an important 

 role and that in general anthracnose becomes widespread only late in 

 the growing season of the crop. Original centers were found in the 

 fields where fruits were only one-third grown, and in some fields infec- 

 tion was still limited to original centers when the fruits were mature. 

 In Georgia, where drought had prevailed, anthracnose was not yet 

 prevalent in the fields, but later, in Florida, after the rainy season 

 had begun, anthracnose was found quite prevalent in the commercial 

 fields, from which shipping had almost ceased, and especially in the 

 immature seed crop. 



At Norfolk, Va., the first week in July, the disease was found in the 

 " original-center " stage in field cucumbers, while it had become 

 widespread and destructive in some of the coldframe beds. 



In 1917 at Madison, Wis., six cucumber fields were under constant 

 observation. This summer was characterized by frequent rains and, 

 except for the last half of July, rather low temperatures. Light rains 



69806°— 18— Bull. 727 5 



