COMPARISON OF THE FUNGICIDAL ACTIVITIES OF (E)-4-HYDROXYLATED STILBENES AND RELATED BIBENZYLS

The fungicidal activities of (E)-4-hydroxylated stilbenes and related bibenzyls were measured by the agar plate procedure and selected active compounds by the soil block method. In the agar plate test, stilbenes with 3'-substituents were all active against two brown-rot (G. trabeum and P. placenta) fungi, with the activity having a parabolic hydrophobic relationship. A highly fungitoxic monomer was used to synthesize a dehydrogenative dimer which showed no brown-rot activity. No stilbene was active against the white-rot fungi C. versicolor while three bibenzyls had white-rot activity. Most bibenzyls had moderate brown-rot fungicidal activity. No structural requirement was apparent for bibenzyl brown-rot activity in contrast to the stilbenes. No synergism was observed when various combinations of stilbenes and bibenzyls were tested by the agar plate procedure. Similarities were observed between the agar plate activity and soil block results, although the soil block required higher levels of the stilbene/bibenzyl. No synergism was observed in the soil block results for stilbene and/or bibenzyl combinations. Stilbenes and/or bibenzyls in combination with didecyldimethylammonium chloride, however, showed some synergism.