Sensitivity of a bio-fungicide component, <i>Bacillus subtilis</i> strain Y1336 to chemical pesticides on cucumber leaves

Sensitivity of Bacillus subtilis strain Y1336 in wettable powder formulation of a biological fungicide to 96 chemical pesticides was investigated on cucumber leaves. Mixtures of the biological fungicide and each of the chemical pesticides as concentrations registered in Japan were dropped onto the leaves. After a week incubation, rise and fall of colony forming units (cfu) of the strain was measured on agar medium. Without chemicals, cfu of the strain slightly decreased to 0.50–0.80 of cfu just after dropping the bio-fungicide without chemicals. Although 32 chemicals at concentrations registered inhibited colony growth of the strain on agar medium, only a fungicide, cyazofamid, and an insecticide, flonicamid, decreased the cfu to <0.10 on the leaves, and 5 fungicides fluazinam, mancozeb, propineb, captan and chinometionat and an insecticide hexiazox decreased the cfu to 0.10–0.20. Cyazofamid, flonicamid and hexiazox did not inhibited growth of the strain on agar medium. These 8 chemicals may interfere the fungicidal effect by the strain.