My fuchsias have gall mites. Will a horticultural oil control them? I would prefer not to use a more toxic pesticide.
Several resources I consulted confirm what you thought about using horticultural oil to control the gall mite problem. The Organic Gardener’s Handbook of Natural Insect and Disease Control (ed. by Ellis and Bradley, 1996) says to spray dormant oil or lime-sulfur on dormant plants.
University of California, Davis’s Integrated Pest Management site has a page about this gall mite, recommending that gardeners “plant only resistant fuchsias and consider replacing susceptible plants. Prune or pinch off and destroy infested terminals. If damage cannot be tolerated, pruning may be followed with two applications of a miticide, applied 2 to 3 weeks apart. Soap or oil sprays provide some control, but cannot kill fuchsia gall mites enclosed in distorted plant tissue.”
According to a May 2004 article from the American Fuchsia Society, “to be effective, [horticultural oil] must come in contact with every live gall mite and smother every gall mite egg. The only way oil products can be effective in killing gall mites is for you to remove the leaves.” Link to this article.