The use of microorganisms is an alternative for the control of plant diseases. However, one should verify its interaction with other methods of control used for a particular crop. The objective of this work was to evaluate the effect of herbicide fungitoxicity on the growth and development of Trichoderma spp. strains. A completely randomized design was used in a factorial scheme 6 x 6 x 4, with four replications. Factor A consisted of the herbicides pendimethalin, clomazone, carfentrazone-ethyl, oxadiazon, thiobencarb + propanyl and byspiribac-sodium; factor B consisted of the herbicides doses 0, 25, 50, 75, 100, and 200% of the recommended dose; and factor C consisted of the Trichoderma spp. strains AJAM 18, CE 66, TRI 01, and TRI 02. The assay was conducted under in vitro conditions, with radial mycelial growth (RMG) and strain sporulation being evaluated after application of the herbicides. A difference was observed in the sensitivity of the strains for the same product tested. Oxadiazon reduced the RMG of the isolates AJAM 18 and TRI 01 in 66% and 35%, respectively. However, it reduced only 16% of the RMG of the isolate TRI 02, and it did not affect the RMG of the isolate CE 66, even when at 200% of the recommended dose. Different effects of the products were verified on each isolate. The commercial mixture thiobencarb+propanyl was highly toxic to the isolates with reduction of the RMG and in the number of spores around 85%. On the other hand, byspiribac-sodium had a little effect on the strains with less than 10% reduction in the RMG and sporulation. Carfentrazone-ethyl and byspiribac-sodium were found to be compatible with the isolates of Trichoderma spp. evaluated.
antagonist; biological control; rice