The steroid phytotoxin viridiol produced by Gliocladium virens is a major limiting factor in the amount of fungus/millet preparation that can be coated on cotton seed to control damping-off incited by Rhizoctonia solani and Pythium ultimum. Treatment of developing G. virens cultures with 0.5-1 ppm of the steroid production inhibitors propiconazole, flusilazol, or triadimenol will suppress viridiol production without adverse effects on fungal growth or biosynthesis of the nonsteroid antibiotics gliotoxin and gliovirin. Greater amounts of antibiotic producing biocontrol preparation can thus be used to treat seed without concomitant phytotoxic effects on the emerging seedling radicle. The efficacy of viridiol suppression by steroid inhibitors is dependent on culture conditions and on the strain of the fungus. At concentrations above 2 ppm, propiconazole and flusilazol are inhibitory to fungus growth. Triadimenol, however, may be used at 10 ppm without apparent effect on growth and with greater suppression of viridiol production.