The Rhizoctonia Damping-Off of Conifers 9 



a little soil from the paths is sprinkled on. The beds are then covered with 

 a single thickness of burlap cloth, which is removed when emergence begins. 

 The burlap is held in place and the beds are protected by wooden lath- 

 covered frames placed flat upon the beds. These are provided with 

 hinged le^s, which can be used to elevate the frames some 8 or 10 inches 

 above the surface of the beds after the burlap has been removed and the 

 seedlings have begun to appear. The strips of lath covering the frames 

 are spaced 1 inch apart, so that partial shade is provided during the two 

 summers that the seedlings are left in the beds. 



PREVALENCE OF THE DISEASE 



The seedbeds at the Ithaca nursery were used for one season only. In 

 order to insure damping-off , the beds were artificially infested with a culture 

 of Rhizoctonia known to be pathogenic to red pine, the one species grown 

 here. The disease was therefore extremely severe at this nursery. An 

 almost complete loss of the seedlings resulted on the untreated plats. 



From the time when the Keene nursery was established in 1906, until 

 the spring of 1924, no serious damping-off was noted there by those in 

 charge. In 1924 the disease appeared rather generally but caused heavy 

 losses only in one corner of the nursery, where from 15 to 20 per cent of 

 damping-off occurred in beds of white pine and norway spruce. 



In 1925 the disease was very destructive in the red-pine and norway- 

 spruce beds, resulting in losses of approximately 50 per cent and 35 per 

 cent, respectively. These figures are rough estimates arrived at by the 

 writer from observations on the final stand as noted during the summer of 

 1926. A section of the red-pine beds as they appeared when the above 

 estimates were made is illustrated in Plate I, 1. The loss in the area 

 photographed was practically 70 per cent. These particular beds were 

 located near the area in which damping-off was severe in 1924. 



The major part of the spring sowing of 1926 was made on a section of 

 the nursery which had never before been used for seedbeds. Contrary 

 to expectations, damping-off was far more severe than at any previous time 

 in the history of the nursery. The seedlings on many beds were almost 

 completely destroyed. Such an area of norway spruce is illustrated in 

 Plate I, 2. The disease became evident with the initial appearance of 

 seedlings of the earliest sowing, and continued to occur throughout the 

 general period of emergence and for several weeks thereafter. It was 

 manifested by an extreme reduction in emergence (particularly in norway 

 spruce), and by the usual damping-off of seedlings after they had appeared 

 above ground. In the case of white pine many seedlings were evidently 

 destroyed by a rotting of the young roots when the stem tissues were 

 already beyond the succulent stage. 



The regular 1927 seeding was made for the most part during the preceding 

 autumn, in a section of the nursery several hundred yards distant from the 



