60 EXPERIMEiNT STATION. [Jan. 



a resistant covering. If applied strong and in sufficient quan- 

 tities it might destroy many of the free-moving forms. When 

 the female has become encysted in the roots of the violet plants 

 it is difficult to conceive how she can become affected without 

 causing injury to the plant. 



Formalin as a remedy for soil organisms has been recently 

 recommended by Prof. A. D. Selby^ of the Ohio Agricultural 

 Experiment Station. The strength recommended is 1 to 200, 

 or 2 pounds (2 pints) of formalin to 50 gallons of water. It 

 is recommended that 1 gallon be applied to each square foot 

 of soil surface. This may be applied by any sprinkling device. 

 Repeated applications of the formalin are made when the crop 

 is removed and at a time when the soil is more or less moist. 

 It is necessary that the soil should not be used for at least 

 two weeks after the application of the formalin. Professor 

 Selby recommends applying the formalin at intervals of a few 

 hours, and the soil should be stirred for a few days after the 

 applications. 



While this treatment is recommended by Professor Selby for 

 such organisms as Rhizoctonia and Sclerotinia, which cause 

 lettuce rots, it is believed not to be applicable for eel worms, 

 since it apparently does not succeed in destroying the more 

 resistant eggs. 



The methods of destroying eel worms in greenhouse soil, with 

 which the writer has experimented for many years, are as 

 follows : — 



Sterilization. — This is one of the cheapest and best methods 

 of destroying eel worms in greenhouse soil. It is necessary that 

 the soil be heated to at least 180° F. and a higher temperature 

 is better. This is accomplished by driving steam through the 

 soil by a system of perforated pipes. 



Freezing. — If the soil is frozen for any length of time the 

 eel worms are destroyed, and some use has been made of this 

 method by practical growers. As a rule, the soil is removed 

 from the house and frozen in bulk out of doors. 



Desiccation. — Drying the soil is destructive to eel worms, 

 but it is difficult to dry soils sufficiently in deep benches to make 



I Circular No. 57, Ohio Agricultural Experiment Station. 



