384 Diseases of Greenhouse Crops 



used to give a nicotine content varying from 0.03 to 

 0.1 percent. 



Table 19 



Soap. Any good soap may effectively be used 

 as a contact insecticide. The best soap is that which 

 is made with caustic potash rather than with caustic 

 soda. Soda soap washes are apt to gelatinize when 

 cold and are made difficult or impossible to be used 

 as a spray. Fir tree oil soap may be used at the 

 rate of three ounces to each five gallons of water 

 without injury to plants. Whale oil soap should be 

 used at the rate of only one-fourth pound to each 

 gallon of water. A stronger solution may injure 

 tender plants. 



Sulphur. This is used not only as a fungicide, but 

 also as an insecticide as well. When used as a fumi- 

 gant, sulphur at the rate of one-third of a pound to 

 each 1,000 cubic feet of greenhouse space will be 

 effective. When ready to fumigate the house is 

 closed tightly, the required amount of sulphur 

 weighed out and divided into four equal parts on 



