256 THE MONTHLY BULLETIN. 



INFECTION. 



The trouble, as before indicated, occurs on the branches, leaves and 

 nuts, and will now be considered more in detail on these parts. 



Nuts of all sizes may be infected at any point on their surface. The 

 spots first appear as small water-soaked areas about the size of a pinhead. 

 This appearance of the disease in its early development is different 

 from its later stage. At this time the infected area is discolored and 

 slightly raised above the healthy tissue. At length the central portion 

 becomes black, but is surrounded by the same water-soaked appearing 

 margin or fermentation zone. With age the entire spot becomes black 

 and no further increase of the diseased tissue takes place. 



The more common infection is at the blossom end or stigma of 

 the small nuts which usually fall from the tree. The stigma is the 

 weakest point of the nut, since it is not protected, as are other parts, 

 by the epidermis, and the infection readily develops and extends 

 within the tissue initil the kernel is l)lackened and destroyed. 



Lateral infection of the nut is that which occurs at other points 

 than the blossom end, and is more common on the larger nuts, while 

 blossom end infection is more abundant on the smaller ones. 



It often happens that favorable conditions occur for natural infec- 

 tion of nuts during the summer months, June and July. At this 

 time the outer tissue is beginning to harden and is not in a condition 

 for the deep development of the disease. In these late infections the 

 development is shallow and does not penetrate much more than 

 through the epidermis. Late blight infections appear as small dark 

 colored areas scattered over the surface of the nut. 



On the branches the disease is confined to small areas, but gradually 

 increases until a lesion or diseased area may extend for two or three 

 inches in length on the green shoot. The disease always begins on the 

 green, succulent growth and often near the growing end. The twig, 

 however, never is killed back for any great distance. In the worst 

 cases the infection may extend downward into the pith, while in less 

 severe ones only the bark and wood become diseased. This diseased 

 area at first develops the same water-soaked appearance as the nuts 

 and then becomes black in color. As the branch becomes more 

 woody, active development of the disease is checked and no more 

 tissue becomes involved. The disease after the first year, even in 

 well defined infected areas, dies out and the tissue again heals up. 

 These diseased portions in many cases have a shrunken, dried-out, 

 deformed, cracked appearance, because of the cracking and drying 

 out of the tissue. 



The leaves are also diseased, especially the petioles and veins, which 

 become a black or brown color. The soft tissue of the leaf is attacked, 

 causing brownish colored spots. Very often the disease appears first 

 on the leaves, from which it spreads to other parts of the tree. No 

 defoliation of the tree results and the disease should not be confused 

 with the falling of the leaves that sometimes occurs during the 

 summer months. 



The catkins are probably never diseased, although after a time, 

 when their work is finished, they become dark colored and dry up. 



Nursery stock is sometimes diseased, large lesions appearing in the 

 rapidly growing stems, and lesser black diseased areas on the smaller 



