Bean Anthracnose 163 



A rainy period of several days accompanied by cool weather is the most 

 favorable condition for infection and for the development of the fungus. 

 Night dew or even humid air, however, is sufficient to allow infection to 

 take place. Conditions permitting the plant to retain moisture beneath 

 the vines are particularly favorable for the infection of the pods. Such 

 conditions are afforded by poor soil drainage, or especially by poor air 

 drainage such as may come about from a bushy growth of vines and from 

 plants growing close together; and similar conditions may exist in a low 

 area or pocket in the field. 



Beans grown at the time of the year when the prevailing weather 

 conditions are the least likely to be favorable for infection, will of course 

 be the freest from anthracnose. Plants inoculated artificially during a 

 rainy day will become badly diseased, while plants in neighboring hills 

 in the same row will be but slightly affected and hills farther on not at 

 all. This is because the weather has remained comparatively dry from 

 the time of inoculation until the pods were maturing, and thus spore 

 dissemination was prevented. The disease does not spread as readily 

 through a field planted in check rows as through one planted in drills. 

 Corbett (1907) says that growers of field beans find the disease worse on 

 crops planted early. In New York State late-maturing beans are the 

 most liable to damage from anthracnose, as weather conditions favorable 

 for infection commonly occur during September. For this reason an early- 

 maturing variety planted early would have a better chance of escaping 

 infection, other things being equal, than a late-maturing one. 



These facts explain why the disease materially decreased during the 

 dry seasons of the four years from 1907 to 1910, and why it has been so 

 severe during years of abundant rainfall. The seed produced in dry seasons 

 is practically free from the disease, and when such seed is used the plants 

 resulting therefrom are remarkably free from anthracnose, even though 

 the season may be wet, because the source of infection is not present. 

 After a season or so of rainy weather, however, the disease, at first 

 inconspicuous, may become general throughout the field and a large amount 

 of spotted seed may result. It has been claimed by seedsmen that in 

 certain irrigated sections of the West where there is but little rainfall 

 during the growing season, plants free from the disease can be grown 

 from spotted seed; but it is questional )le whether the moist conditions 

 beneath the vines resulting from irrigation would not be sufficiently 



