24 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



seedlings (82) as well as for pines, to prevent by soil disinfection 

 losses before the seedlings appear above the ground. Heat disinfec- 

 tion of seed beds has been frequently mentioned. Burning wood 

 or litter on the surface of the beds before sowing, said by Gilbert (47, 

 p. 36) to be a common procedure in preparing tobacco seed beds both 

 in Italy and in parts of this country, has been recommended for 

 coniferous seed beds by Biittner (25). The disadvantageous results 

 sometimes noticed following the application of wood ashes to pine 

 seed beds may prove an objection to this type of treatment in some 

 of the nurseries. At a Nebraska nursery (67) moist heat proved only 

 partly satisfactory, unavoidable reinfection having serious results. 

 Steam disinfection, using the inverted-pan method commonly advo- 

 cated for tobacco seedlings (10, 47, 81), has been reported by Scott 

 (123) as successful at a nursery in Kansas. Gifford (46) found 

 steaming with the inverted pan only partly satisfactory. It is not 

 believed that it is likely to pay to install the necessary apparatus for 

 steam disinfection at nurseries in nonagricultural districts where 

 steam tractors are not available for temporary use. The hot-water 

 soil treatment as used by Byars and Gilbert (27) is probably worth 

 a trial at any nursery where damping-off is serious and fuel cheap. 

 It ma}' be that in some localities where steam or hot-water treatment 

 of the soil is not sufficiently effective, its efficiency can be increased 

 by reinoculating the soil immediately after treatment with sapro- 

 phytic molds and bacteria to provide maximum competition for 

 parasites which come in from the outside. Tests of this procedure 

 will be described later in the present bulletin. The value of char- 

 coal has been emphasized by Retan (109, 110). 



Chemical disinfection of the soil has also been employed. Sulphur 

 has long been in use as a soil treatment against the damping-off of 

 various plants (45, 111) in addition to its use in combating potato 

 scab and onion smut. It was tested on conifers by Spaulding (136, 

 137) in the form of light surface applications to the beds after ger- 

 mination, but without decisive result. In later cooperative tests pow- 

 dered sulphur raked into the soil before the sowing of the seed failed 

 to indicate any large measure of value. Very finely divided forms 

 of sulphur in various amounts and times of application are prob- 

 ably worth some further test. 



Moller (90) and Sherbakoff (128) have reported the successful use 

 of copper sulphate in combating attacks of Corticium on dicotyle- 

 dons. In Johnson's experiments on tobacco seedlings (82, table 

 3) copper salts and Bordeaux mixture were the only chemicals for 

 which any value was indicated. Sherbakoff apparently used copper 

 sulphate and other strong disinfectants chiefly to stop the extension 

 of vigorously spreading damping-off foci by local treatment rather 

 than as a general treatment for use over the beds. Such treatment 



