6 



immune to the blight. This applies, however, only to trees grown 

 from imported nuts or nursery stock. These trees hybridize very 

 readily with the native trees, and trees grown from seed produced in 

 this country appear to lose their power of immunity. 



RECOGNIZING THE DISEASE 



Owners of valuable chestnut trees in Pennsylvania should learn 

 at once to recognize all the symptoms of the blight, so that it may be 

 speedily detected as soon as it appears. 



Briefly stated, the disease may be located and recognized by some 

 or all of the following characteristics: 



1. Dead branches, usually with withered leaves clinging to them. 

 In the spring, prior to death, the leaves on the infected branches 

 remain small and sickly looking, and gradually take on a yellowish 

 tinge. When these leaves finally die, they have a peculiar wilted 

 appearance. The burrs also remain small and undeveloped. On 

 branches attacked after the leaves have fully developed, the leaves 

 assume their yellowish or reddish-brown fall colors. On trees killed 

 by blight during the growing season prior to September, both leaves 

 and burrs usually remain clinging to the branches through the fol- 

 lowing winter and are of great value in helping to locate infected 

 trees. All dead branches should be closely examined for further in- 

 dications of the disease, particularly at the base of the dead parts. 



2. Cankers on diseased branches or the trunk, where the bark 

 is not thick and rough. These cankers are areas of dead, discolored, 

 sunken bark, often more or less broken by cracks or checks into the 

 inner bark. Old, thick bark does not change in outward appearance 

 until a year or so after it is diseased, when it begins to peel from the 

 tree in shreds. Prior to shredding, thick bark which is affected 

 gives forth a peculiar hollow sound when struck with a hammer, 

 due to a space between the wood and bark caused by the decay of 

 the inner bark. 



3. Small reddish blisters appear on cankers on smooth bark. 

 Later the tops of these blisters burst, forming small, wartlike erup- 

 tions or pustules of a sulphur-yellow, orange, or brown color. In 

 the deep cracks of old bark, the pustules form reddish or orange- 

 colored lines. These pustules are the fruiting bodies which produce 

 the spores. During damp weather bright yellow, twisted threads of 

 the microscopic spores are sent out from the pustules. These threads 

 are jelly-like at first but on drying become firm and brittle. They vary 

 from one-sixteenth to half an inch in length, and are dissolved by the 

 rain, which distributes the spores down the surface of the bark. 



