244 INSECTS, DISEASES AND OTHER PESTS 



more important than the regulating of the temperature in 

 the houses. 



We come now to the question of: "How does the 

 fungus Rhizoctonia get into the house ? " Sometimes the 

 plants in the field will show no signs of disease at all and 

 still when the plants are brought into the house a large 

 number will be lost. There is no question that the fungus 

 Rhizoctonia is brought in with the soil and manure from 

 the field or compost bed. Even so-called " virgin soil " 

 will harbor the fungus. The fungus Rhizoctonia has a 

 large range of hosts among field crops, vegetables, flori- 

 cultural plants and weeds. Experiment? have shown that 

 the Rhizoctonia attacking one plant is the same form that 

 attacks another. 



The fungus Rhizoctonia has been found attacking 

 weeds like the Thistle, Lamb's-quarters, Pigweed, Rag- 

 weed, yellow Mustard, Dock and many others which are 

 generally found growing in fields and pastures. The 

 same fungus also attacks Clover, which is usually sown 

 in sod. It is clearly seen then that the soil used for com- 

 post is, as a rule, infected with the fungus Rhizoctonia, 

 which causes the stem rot of Carnations. When the sod 

 is composted with manure, the fungus is able to live for 

 several years, so that it is still present when the soil is 

 brought into the house. 



The use of limestone in the compost will help ma- 

 terially in the suppression of the fungus, while if the 

 Carnation field and houses become badly infected the 

 grower must resort to sterilization of the soil. A number 

 of experiments are in progress and the results to date 

 tend to show that steam sterilization is the best means 

 of killing the fungus in the soil that is brought into the 

 house. 



