Answer: Horticultural oil is typically sprayed on dormant plants, not plants with green leaves. The oil residue effectively suffocated the leaves of your plants. Some leaves are less susceptible to the effects of horticultural oil and others are extremely sensitive. The best course of action I can recommend is to use products according to label directions and to make sure that both the pest and the plant you're using it on are listed on the label. As you've discovered, not all products are safe to use on all plants against all pests. At this point, all you can do is continue to prune any leaves that die and keep the oil spray away from these plants in the future. Best wishes with your plants!
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