Use of Trichoderma harzianum and Gliocladium vitens for the Biological Control of Post‐emergence Damping‐off and Root Rot of Cucumbers Caused by Pythium ultimum

Abstract The antagonist strains Gliocladium virens G2 and Trichoderma harzianum T3 originally isolated from Pythium suppressive peat, and two benomyl‐resistant strains of T. harzianum, T12B and T95, were evaluated as biological control agents of damping‐off and root rot of cucumbers in sphagnum peat caused by Pythium ultimum. All strains were equally effective when applied as 1 % peat‐bran preparations, whereas the effectiveness of disease control was reduced at higher concentrations of the antagonists. The two wild‐type strains were also found to be effective when applied as conidial suspensions, and in this case no reduction in disease control was seen at higher concentrations. G. virens G2 and T. harzianum T12B showed antibiotic activity against P. ultimum in in vitro tests; however there were no signs of mycoparasitism of P. ultimum by any of the antagonist strains.