Slaked Lime, Baking Soda And Mineral Oil For Black Spot And Powdery Mildew Control In Apples

Five apple field trials investigated the effects of alternative fungicides on apple black spot (Venturia inaequalis), powdery mildew (Podosphaera leucotricha), European red mite (Panonychus ulmi) and the predatory mite (Typhlodromus pyri). Slaked lime (calcium hydroxide) controlled black spot but not powdery mildew and addition of mineral oil (Sunspray Ultrafine) had little effect, Baking soda (sodium bicarbonate) gave about the same degree of black spot control as slaked lime and also gave slight control of powdery mildew. Addition of mineral oil to baking soda appeared to improve powdery mildew control but not black spot control. A cupric hydroxide plus sulphur mixture gave better black spot control than slaked lime or baking soda and a programme of conventional synthetic fungicides gave better black spot and powdery mildew control than baking soda and oil. Slaked lime reduced predator mite numbers and might therefore disrupt integrated mite control. Neither baking soda nor oil (125 ml/100 litres water) affected mite numbers.