THE CHESTNUT BLIGHT. 



Mr. Keller E. Rockey, in charge of Demonstration Work, Penn- 

 sylvania Chestnut Tree Blight Commission. 



In 1904 the diseased condition of the chestnut trees around 

 New York City was noted, and an examination of them showed that 

 they were being attacked by a fungus disease which was unknown at 

 that time. It has since been found that the disease had been present 

 there and elsewhere for some years before that time, but is impos- 

 sible to determine when it first appeared. The disease was studied 

 and classified during the winter of that year. It was placed in the 

 genus Diaporthe and nam.ed Diaporthe Parasitica, making it a new 

 species of a genus which contained only harmless fungi. The dis- 

 ease is commonly called the ''chestnut blight" or the "chestnut 

 canker disease." It is a fungus or a low order of plant life which 

 grows upon the cells of the bark and to some extent the wood of the 

 chestnut tree. The disease advances in each direction, the tissues of 

 the cells are broken down, the flow of sap is cut oflf, and the tree 

 killed by girdling. The disease is spread to other parts of the tree 

 and to other trees by means of spores. These spores are of two 

 kinds, called for convenience the summer and winter spores, al- 

 though both types are produced to some extent at nearly all seasons 

 of the year. The summer spores may be seen coming out from the 

 pustules in small threads after the manner of paste squeezed from 

 a tube. These threads are yellow, about one-quarter of an inch 

 long, and are forced out shortly after a rain. These spores are 

 readily dissolved in water and wash down the trees, infecting them in 

 other places. They are sticky and carried, to some extent, by in- 

 sects. The winter spores are shot out into the air when the bark is 

 soaked after a rain and are disseminated chiefly by the wind. 



On display here are specimens and photographs showing the 

 appearance of the blight so that I will not go into that part of the 

 subject in detail. I hope, however, that you will notice: ist. The 

 small, red pustules which bear the spores and appear only in the 

 crevices of rough barked trees. 2d. The peculiar mottled appear- 

 ance of the inner bark of the canker with the fan-shaped mycelium. 

 By either of these characteristics, the disease may be identified. 



In scouting for the chestnut blight there are danger signals 

 which make the work easier and more accurate. A canker, espe- 

 cially on smooth bark, will very shortly discolor the outer bark, 

 turning it from green to reddish brown tint. On young growth the 

 cankers cause a hypertrophy or swelling which is very evident as 

 you will see by the specimens. The bark over the cankers usually 

 cracks open and a closer examination will reveal the pustules grow- 



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