The Rhizoctonia Damping-Off of Conifers 57 



found effective in these experiments. Of the different materials tested, 

 aluminum sulfate was the most inexpensive. The cost given is for the 

 commercial grade, which was equally as effective as the more expensive 

 technical grade. The organic-mercury preparations, particularly the 

 dusts, were the most expensive of the materials used. In view of the 

 fact that most of these have but recently appeared on the market, it is 

 possible that the prices will be reduced with greater volume of production. 

 The factors of time and labor involved in applying treatments must also 

 be considered along with the cost of chemicals. From this point of view 

 the application of dry chemicals has much in its favor, since the incon- 

 venience and the expense of handling large quantities of water are avoided. 

 A further advantage of the use of dry chemicals is the ease with which the 

 materials can be worked into the soil during the regular operations of 

 preparing the seedbeds. The only added labor involved is that required 

 to sift the chemical on the surface of the beds prior to the final raking. 



GENERAL DISCUSSION AND CONCLUSIONS 



A number of widely varying factors are necessarily involved in any 

 discussion of damping-off. It is perhaps fortunate that in most of these 

 investigations the causal organism was fairly constant throughout. It 

 has been pointed out that while a number of different forms of Rhizoctonia 

 were isolated from diseased seedlings, the majority of strains from the 

 Keene nursery were strikingly similar. This fact is of advantage in 

 making different soil-treatment experiments comparable to one another. 

 One cannot, of course, draw too definite conclusions as to the results which 

 may be expected where fungi other than Rhizoctonia are involved. Some 

 information is available, however, from the Ithaca experiment, where 

 Pythium was present throughout the beds and caused at least a part 

 of the losses. 



During the course of the early field experiments, considerable attention 

 was given to the most desirable time for making soil treatments. It 

 was hoped that some of the mercury materials would be found effective for 

 use in checking epiphytotics of damping-off if applied after the disease 

 first became evident. It was soon realized, however, that losses resulting 

 from the killing of the germinating seeds and seedlings by the fungus 

 before they appeared above ground, made such treatments impracticable. 



One of the most outstanding features of these investigations has been 

 the rather uniformly successful control of damping-off obtained through a 

 single application at the time of seeding, with certain concentrations of 

 nearly all of the materials tested. This is particularly striking in view of 

 the heavy losses in the untreated plats. Thus, in many experiments the 

 increase in final stand with most treatments over that of the check was as 

 high as 200 to 300 per cent. 



The experiments of 1927 have demonstrated that successful control of 

 damping-off can be obtained by the use of dry applications of aluminum 



