Use of Oospore Formulations of Pythium oligandrum for Biological Control of Pythium Damping‐off in Cress

Abstrac Oospore preparations of Pythium oligandrum produced by liquid and solid‐substrate fermentations were evaluated for biocontrol activity against Pythium damping‐off in cress in artificially infested sand and naturally infested soil. Oospore biomass preparations from liquid fermentation of six isolates of P. oligandrum were equally effective in reducing damping‐off in sand when tested as seed‐coatings, whereas this type of preparation of a single isolate formulated as a kaolin dust, on Perlite and as alginate pellets incorporated into sand gave little or no control. None of the formulations containing oospores produced by solid‐substrate fermentation incorporated into sand had any effect. In soil, a formulation containing oospores produced in a barley‐Perlite solid‐substrate fermentation and all oospore‐biomass formulations which were prepared increased seedling survival, but none of these were as effective as a propamocarb HCl drench.