Use of Soil Inoculants 



301 



fungi may prove to be most effieient in increasing the value of the 

 treatment. Whether the saprophytic fungus uses up the available 

 nutrients rendered sokible on steaming of soil or whether the favor- 



100 



80 



"5 60 



S 40 



20 



5.0 



9.0 



Fig. 120. Effect of pH upon occurrence of root rot and wilt (from Taubenhaus 



et al. ) . 



able effect is due to the production of a substance directly injurious 

 to the plant pathogen, remains to be determined. 



Use of Soil Inoculants 



The methods of biological control of disease-producing organisms 

 are still insufficiently studied. Here belong the introduction of 

 birds and other higher animals, as well as of certain insects feeding 

 upon specific injurious insects and worms, or the use of predaceous 

 nematodes against plant-pathogenic nematodes, or of entomogenous 

 fungi and bacteria parasitic upon insects. The phenomena of an- 

 tagonism may also be listed here. 



Numerous attempts have been made to inoculate the soil with 

 antagonistic organisms for the purpose of controlling plant diseases. 

 These efforts have proved to be, in most instances, complete failures, 

 as pointed out previously. This is largely because, unless the condi- 



