TWIN-SCREW EXTRUSION OF PESTA-ENCAPSULATED BIOCONTROL AGENTS

`Pesta' granules in which fungal propagules are encapsulated in a whea t gluten matrix were prepared in multi-pound quantities by twin-screw extrusion and fluid bed drying. Dough formulations for extrusion conta ined wheat flour and kaolin, or wheat flour, kaolin and rice flour, pl us water and fungal inoculum. Conidial inoculum of truncatum, a pathog en of the weed hemp sesbania (Sesbania survived laboratory scale Colle totrichum exaltata), dough preparation [100% retention of colony-formi ng units (c.f.u.)] better than dough preparation for twin-screw extrus ion (8-10% c.f.u. retention). The loss in viability was linked to the lower water content of dough used in the twin-screw extruder. Fluid be d drying reduced viability further to 1%. Retention of viability after twin-screw extrusion and fluid bed drying at 35-50 degrees C was 35% with conjuncta/infectoria, a pathogen of swamp dodder (Cuscuta gronovi i). Retention was 86-100% with atoxigenic strains of Aspergillus flavu s and Aspergillus parasiticus used as biocompetitors to reduce aflatox in levels in peanuts. In the greenhouse, twin-screw-extruded granules containing C. (at about 5 x 10(4) c.f.u. g(-1)) caused high levels of infection and mortality in hemp sesbania seedlings.