286 



Bulletin 239. 



If, after having carefully studied this key and tlie photographs, you 

 are not satisfied which disease you have on your beans, send some of the 

 affected plants to the Plant Pathologist, Cornell University Experiment 

 Station, Ithaca, N. Y. He will be glad to make an examination and 

 report to you. Having determined which disease is giving you trouble, 

 turn to the page indicated and carefully read the description and treatment 

 for that disease. You will frequently find both the anthracnose and the 

 blight on the same plant, and sometimes even the rust also. 



I\ 



I. BEAN ANTHRACNOSE 



The anthracnose is at present the most common and 

 destructive disease of beans in this State. It is very 

 probably the disease that is destroying your crop. Its 

 most apparent injury is on the pods, wdiere it forms 

 large dark rusty brown or black spots (See cover). 

 It is on this account frequently known as " pod-spot." 

 The disease may and usually does occur, however, on 

 all parts of the plant except the roots (Fig. loi). 

 It is caused by a fungus known to botanists as (Col- 

 Ictotrichuin Undcmuthianum) which lives as a parasite 

 in the tissues of the bean. This fungus is a plant, as 

 much a plant as the bean on which it lives. It has a 

 thread-like mycelium that grows into the tissue of the 

 bean to obtain food for its growth and development 

 and it produces spores that serve the purpose of seeds 

 by which it spreads to healthy beans and so reproduces 

 itself. In fighting the anthracnose fungus, we are 

 fighting a parasitic weed, in its habits not greatly unlike 

 the dodder which often destroys alfalfa. 



The fungus itself is too minute to be seen by the un- 

 aided eye. This makes an understanding of its nature 

 and ways of life rather difficult, but the picture of the 

 parasite as shown in hig. 105 will help to make clear 

 the discussion of the disease. Study the picture care- 

 fully before reading the following account. 

 TJic disease on seedlini::;s. — The disease makes its first appearance on 

 the bean seedlings, as they come up. It may then be detected, on at least 

 some of the yovmg plants, as brown discolored sunken spots or cankers 

 on the seed-leaves or the stem (Fig. 103). This early appearance of the 

 disease is due to the fact that the fungus is usually carried over winter 

 in the seed and so is already in the bean when it is planted. This is fully 

 explained later ( Page 289) . In severe cases the spots or cankers may be 



Fig. 103. — Bean 

 seedling showing 

 the anthracnose 

 spots ons tern and 

 seed-leaves 

 {After Ilalstcd). 



i 



