2 BULLETIjST 818^ U. S. DEPARTMENT OF AGRICULTURE. 



successfully. It is not thought that the hot-water method will 

 take the place of steam for soil-disinfecting purposes where steam 

 can be advantageously used. On the other hand, it is intended for 

 use where steam is not available or where its use is for any reason im- 

 practicable. Many greenhouses are so constructed that the use of 

 inverted pans for steaming the soil is not feasible. In some green- 

 houses the capacity of the boilers is not sufficient to furnish the high 

 pressure steam required for disinfecting purposes. For disinfecting 

 small quantities of soil in pots or flats, to be used in growing seedling 

 plants for home gardens or in greenhouses, steam is rarely available, 

 and its use is often impracticable. 



So far as the writers have been able to ascertain, the only investi- 

 gations that have been carried out with hot water for soil disinfec- 

 tion are those of Stone and Smith in ''The Rotting of Greenhouse 

 Lettuce," Bulletin 69 of the Massachusetts (Hatch) Agricultural 

 Experiment Station, published in 1900. Working with deep ground 

 beds of greenhouse soil, they found that by the liberal application of 

 water at 210° F. as it came from the hose the temperature of the 

 upper 4 inches of soil was raised to 176° to 186° F. The treatment 

 completely killed the Rhizoctonia and reduced the amount of 

 lettuce drop caused by Sclerotinia lihertiana 76 per cent. 



In carrying out the investigations here reported, two series of 

 experiments were performed, tiie second being in a large measure a 

 repetition of the first, but with certain changes and, additions 

 suggested as a result of the first tests, 



EXPERIMENT SERIES I. 



METHOD OF PROCEDURE. 



SOIL. 



The soil used in the experiments was a light, loose, sandy mixture 

 made of about one-third standard greenhouse soil and two-thu-ds sand. 

 Such a mixture is very favorable for the growth of nematodes. 

 For some time previous to the initiation of the experiments, the soU 

 had been in a bench section in the greenhouse which had been used 

 for growing tomatoes for maintaining a large stock culture of nema- 

 todes. It was, therefore, well infested with the root-knot nematode 

 and with damping-off fungi, as was shown by previous results on 

 tomatoes grown thereui as well by the subsequent observations with 

 untreated checks. To msure uniform physical condition and uniform 

 distribution of the pathogenes throughout the entire mass of soil, it 

 was thoroughly mixed by shoveling over several times, and was then 

 sifted through a coarse screen. To obtain more abundant infection, in 

 in some cases, as noted in detail below, tomato roots severely diseased 

 with root-knot were cut up into small pieces and mixed with the soil. 



