49 

 amended soils late in the season may have been due to increases in 



populations of antagonists , which were greater in amended than in non- 

 amended soils. The increase in the pathogen population in nonamended 

 soils late in the season may have been due to sporulation on the above- 

 ground lesions or to saprophytic proliferation of the pathogen on fresh 

 plant debris. The lack of an increase in pathogen populations in 

 amended soils also may be important in reducing the amount of inoculum 

 available for infection in succeeding years. 



The high populations of T. harzianum in amended soils and the 

 failure to detect A. ochraceus in nonamended soils indicate that the 

 addition of antagonists led to the establishment of populations of the 

 organisms in amended soils; howeveri it was not possible to determine if 

 the populations of the specific isolates of the antagonists actually 

 originated from the added antagonists. 



The applicability of the antagonist amendments to production 

 systems is realized when one considers that three 15-cm petri plate 



cultures of each antagonist grown on potato dextrose agar produced 



in- 

 sufficient inoculum to infest approximately 10 tomato plants at the 



prescribed rate of 5 X 10-' conidia of each isolate per plant. The 

 application of the antagonists by a drench either before or after 

 planting could be effective in controlling the disease. It is impor- 

 tant, however, that antagonists recolonize the soil before reinfestation 

 by the pathogen occurs. 



The increase in disease severity that follows the application of a 

 broad spectrum biocide to soils has been reported (4,17126,38). The 

 usual explanation for this phenomenon is that the disturbance of the 

 microbial community increases the ability of a pathogen to proliferate 



