Attempts were made to control black root rot of apple with the fungicides, benomyl, captan, thiabendazole and triarimol, and to determine their fungitoxic effects on the causal pathogen Xylaria mali. The pathogen responded differently in various bioassay methods, but all fungicides were inhibitory to its vegetative growth.

Disease control was evaluated by applying the fungicides as amendments or as drenches to the soil in which the roots were artificially inoculated. The best therapy was obtained with a captan drench (4,000 ppm), followed by captan (1,000 ppm) and benomyl (300 ppm) drenches, Root growth was suppressed at all higher concentrations except with captan; root development was directly correlated with chemotherapy.

Fungitoxicants were recovered from leaves of seedlings treated with all fungicides except triarimol. Higher bioassay activity was observed in plants treated by the soil amendment method. Leaves from benomyl-treated plants exhibited the greatest bioassay activity.