Hema Kasinathan Thesis May 1 2012.pdf - Atrium - University of ...

Biofungicides have been included as a component of IPM programs to managevarious pathogens when effective products are available, especially in organic productionor where other options are limited. However, the results of the current study indicate thatthe use of biofungicides to manage P. brassicae under field conditions will bechallenging. The biofungicides Prestop and Serenade reduced clubroot up to 50% ingrowth room trials where the inoculum pressure was maintained at a low to moderatelevel (5 x 10 5 spores mL -1 ), but were not effective under field conditions where the sporeconcentrations were up to 3 x 10 7 spores g -1 of soil. Besides inoculum pressure, one factorthat might be important in the efficacy of the biofungicides is the rate and volume of thebiofungicide products. There may have been insufficient biocontrol agent to colonizeand protect the roots of treated plants in the field study. Even though the products wereapplied at 5 times the label rate in both cases, the final volume that each plant receiveddiffered between the growth room and the field trials. In the growth room trials, eachseedling received 50 mL of biofungicide solution (for example, 2.5 mL of Serenade in 50mL solution), but each plant in the field trials received only 1–5 mL of biofungicidesolution (0.08 mL of Serenade in 1.8 mL solution). It is to be noted that in napa cabbagefield trials, 100 mL of biofungicides solution was applied in 2010 to each transplant, butin 2011, 25 mL was applied to each 2-wk-old transplant to colonize the roots prior to theexposure of pathogen. High levels of clubroot were observed in both trials. In this case,the host and cultivar susceptibility played a more important role than biofungicide rate orvolume.In addition to biofungicide concentration, other factors such as the amount andtiming of rainfall, host susceptibility, pathotype, and soil properties were also shown to109