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



ton (14) finds the summer heat of Louisiana inhibiting bean anthrac- 

 nose, and a similar situation may have existed in the case under 

 consideration. 



Very heavy rainfall on August 3,4, and 5 was followed by a marked 

 spread of the disease in fields 1 and 2. A rather careful inspection 

 of field 1 on August 15 disclosed about 26 more or less distinct addi- 

 tional centers of infection, accompanied by rather widely scattered 

 secondary infection in many cases. A similar situation obtained in 

 field 2, and careful inspections on August 11 and 14 yielded a total 

 of about 30 centers of infection, around most of which there was 

 extensive secondary infection. This tended to extend farthest in 

 the direction of the slope of the land and will be referred to later 

 in connection with the consideration of water dissemination. On 

 August 17 the disease was generally distributed in field 3 among the 

 plants which had not been removed, especially at the lower corner 

 of the field. A small private patch adjacent to this corner and hith- 

 erto undiseased, which received much of the drainage from field 3, 

 also showed much infection of uniform age about this time. In field 

 4, occupying a very gentle slope, the disease did not become preva- 

 lent. By August 18 there were 10 centers in field 5 from which con- 

 siderable spread had occurred, notably in the direction of the slope. 

 Since an incubation period of a week or more is quite normal in the 

 field, this first general spread of the disease seems to be closely asso- 

 ciated with the period of abundant rainfall above mentioned. 



During the week after August 18 the destructive effect of the 

 disease became very apparent; the centers of infection were character- 

 ized by the death of the older diseased leaves and the rapid blighting of 

 those near by. New centers of infection were found among the plant- 

 ings of cucurbit varieties. Some new infection, due perhaps to the light 

 rain of August 10, also appeared, but nowhere in such abundance as 

 the infection which followed the heavy showers of the first of the 

 month. Here it should be noted that, following this rain, the daily 

 mean temperatures were quite low for five days. Occasional incipient 

 lesions appearing within the infected areas previous to the rain of 

 August 26 indicate that rain is not essential to infection. An hypoth- 

 esis to account for the latter phenomenon is that, while rain is essen- 

 tial to the actual dissemination of the spores, germination and infec- 

 tion may occur later in the heavy dew which is formed during clear 

 nights in August. 



No anthracnose appeared in field 19, occupying level muck soil, 

 until August 24, and it then remained confined to two small centers. 

 In fields 9 and 10, belonging to private growers, no anthracnose 

 appeared during this season. 



Observations of August 21 to 31 made upon fields 1 and 2 showed 

 that, as a rule, no marked extension of the areas of infection had 



