150 HATCH EXPERIMENT STATION. [Jan. 



be the relation between the drop fungus and Bofrytis, it is 

 certain that the disease is not spread by Botrytis spores in 

 the air, but by a mycelium or mould-like growth in the soil 

 itself. 



Our control experiments have so far been along three dif- 

 ferent lines ; namely, those in which chemical substances 

 were used on the soil, the application of various gases to 

 the greenhouse, and the effect of different layers of sand and 

 sterilized earth. The results obtained by the use of chemical 

 substances have been entirely negative, and the use of gases 

 does not at the present time give great encouragement. In 

 our last report we called attention to the use of sterilized 

 soil as a possible control method, and during the past winter 

 and also at the present time this method has been in use. 

 Our experiments have shown that the heating method is the 

 only absolute one, although some gain has been made by the 

 use of three-fourths of an inch of sand upon the beds. The 

 sand which was sterilized showed better results than the un- 

 sterilized. In both instances, however, cleaner and better 

 plants have been obtained by the use of three-fourths or one- 

 half of an inch placed upon the surface of the soil. Ex- 

 periments in which three or four inches of the top soil was 

 sterilized gave absolute results in the control of the drop, and 

 those in which two inches of the infected top soil was steril- 

 ized have not as yet shown any evidences of the drop. Where 

 one inch of sterilized soil was used and carefully distributed, 

 the loss from the drop has been about four per cent., while 

 in the adjacent beds which were not sterilized the loss was 

 about fifty per cent. These experiments have been carried 

 out in another badly infested house, managed by an experi- 

 enced lettuce grower, on a much larger scale, with quite sim- 

 ilar results. 



While this method gives promise of being a practical one, 

 we are not quite certain as yet whether it is the cheapest one 

 which can be utilized, and other control methods are being ex- 

 perimented with. Some growers clean their houses out every 

 year, and put in fresh subsoil mixed with horse manure ; 

 but such a method is expensive, probably more so than the 

 heating of an inch or two of the top soil previous to planting 



