Horticultural oil Posted on November 8, 2022November 8, 2022 by Tex Norwood A light refined horticultural oil used during the growing season to control insect pests and diseases. Related Articles: Plumeria Care RegimenMealybug – PestAphids – PestAlternative Meanings: Horticultural oilAn oil made from petroleum products, vegetable oil, or fish oil used to control insect pests and diseases. Oils work by smothering insects and their eggs and by protectively coating buds against pathogen entry.