The effect of five common orchard fungicides, captan, dodine, dichlone, glyodin, and a mercuric acetate eradicant, on the activity of a wettable powder preparation of spores of Bacillus thuringiensis Berliner was studied in the laboratory, orchard, and field, using pests of apple and cabbage as test insects. Glyodin was the only one of the fungicides tested in the laboratory that significantly reduced the activity of the spores against larvae of the eastern tent caterpillar, Malacosoma americanum (Fabricius), and the winter moth, Operophthera brumata (Linnaeus). In the orchard and field tests the combining of glyodin or dodine with sprays of the spores reduced mortality of larvae of the winter moth, the imported cabbageworm, Pieris rapae (Linnaeus), and the diamondback moth, Plutella maculipennis (Curtis).
