6 BULLETIN 89, U. S. DEPARTMENT OF AGRICULTURE. 



NUMBER AND SIZE OF POPLAR TREES KILLED BY ARMILLARIA MELLEA. 



Ill addition to the dead chestnuts and oaks, the writer counted 29 

 poplar trees which had been killed by this root-rot out of a total 

 of 45 examined. Many of these were small and much suppressed, 

 although there were 12 that ranged from 6 to 9 inches in diameter. 

 These larger poplars were not suppressed and under normal condi- 

 tions ought not to have died. 



GENERAL DISCUSSION OF THE DISEASED CHESTNUTS AND OAKS. 



Why a larger percentage of small white oaks should be killed than 

 of small chestnut trees is difficult to explain from the data at hand. 

 However, it seems to be evident, judging from the location of the 

 smaller white oaks which were killed, that the majority of the trees 

 under 1 1 inches in diameter were much suppressed and for this reason 

 would perhaps succumb more quickly to disease than trees growing 

 under more favorable conditions. Nothing was found to indicate that 

 the larger white oaks which had been killed were in poor health 

 before they were attacked by this disease. It would seem that the 

 disease, having gained a foothold in the soil, simply spread to the 

 large white oaks and finally killed them. As far as could be deter- 

 mined, the fungus Armillaria mellea was the primary cause of their 

 death. No white oaks in this region were seen which had been 

 struck by lightning; this was in marked contrast to the number of 

 chestnut trees in the same territory which had been struck. 



The only explanation which can be offered for the small percentage 

 of young chestnut trees which had been killed by the root-rot is that 

 the present stand of chestnuts originated mainly from sprouts, and 

 the young trees therefore had the large root system of the parent 

 stump from which to draw nourishment. As a result, their growth 

 would be very vigorous during the first 10 or 15 years of life. Under 

 such conditions one would not expect a hemiparasite like Armillaria 

 mellea to attack them as readily as it did the suppressed young oaks. 

 This, however, does not explain why the disease has killed so many 

 of the older and larger chestnut trees, unless the old stumps acted' 

 as a breeding ground for the mycelium until it obtained a foothold 

 in the living trees. The chestnuts undoubtedly were growing under 

 unfavorable conditions, a fact proved by the very small annual incre- 

 ment. This would make them more subject to diseases of this type. 

 The weather conditions in the past may have been such as to weaken 

 the trees and thus make them more susceptible to this rot. For 

 instance, in the year 1913 the chestnut trees had lost two sets of leaves 

 from late frosts, and at the time this investigation was made (June 

 19, 1913) the third set of leaves was not fully developed, and many 

 of the trees were so badly injured that they apparently were not 

 going to leaf out at all. 



