342 OHIO EXPERIMENT STATION: BULLETIN 214 
Under the diseases described for each plant, methods of avoid- 
ance and treatment are indicated and the diligent student will find 
other instances of similar character mentioned therein. 
SOIL TREATMENT IN THE FORCING HOUSE 
About our great centers of population have grown up conspicu- 
ous developments of the forcing house industry; large areas are 
covered with glass and these hothouses are maintained at the 
necessary temperatures for the production of the special green 
crops found profitable, At the same time the soil of the hothouse 
beds is very liberally manured and enriched further by applications 
of commercial fertilizers. Not only do these applications of manure 
tend to enrich the flora of the soil and to introduce particular root 
parasites, but the decay of the organic matter of the manure also 
tends to produce humus acids in considerable quantities. Along with 
these are brought parasitic eelworms which are peculiarly fatal to 
curcurbitaceous plants, to violets and to some other hothouse crops. 
_ Next to the eelworms the most conspicuous organism in our area is 
the sterile fungus Rhizoctonia, whose resting formsor sclerotia may 
be readily introduced in manure. To meet this indoor soil infection, 
special methods of soil sterilization had to be developed, since soil 
rotation is practically impossible in the forcing house. 
These methods of treatment are in brief, steaming oi the soil to 
render it practically sterile, so far as these parasites are concerned, 
and a method of formalin drenching. This method of steaming is 
ideal, or almost so, in its results upon sandy or loamy soils, but often 
entails unfavorable changes in heavy silty or clay soils. Essentially, 
it consists in burying a series of perforated pipes in the soil at inter- 
vals, covering the surface of the beds and passing live steam in suffic- 
ient volume into the pipes. These pipes are prepared insets with cross 
heads and boiler connections and are perforated at desired distances. 
The surface of the bed is covered with canvas and the steam passed 
into the system for such period as is required to heat the soil toa 
temperature from 180° to 212° Fahz., to be maintained for one hour 
or more. ‘This applies to high pressure boilers; for low pressure or 
hot water heating systems where the steam is applied in subdrains, 
four to five hours steaming will be required with a pressure of six 
to seven pounds. ‘This treatment is effective for destruction of the 
eelworms or nematodes of cucumbers, violets and | lettuce, the rot or 
drop fungus of lettuce, the rosette fungus, and in general of all soil 
infesting parasites. 
