Hibiscus plants require cultivated loam and peat soil, direct sunlight and daily watering. While these flowers are already high maintenance, white leaf spots regularly complicate hibiscus growing. White hibiscus leaf spots are a common but serious concern for your plant's health.
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Mildew is typically responsible for white spots on hibiscus leaves. Spider mites can also cause white leaf spots. Spider mites sometimes attack hibiscus plants, so do not write off this possible cause, but mites prefer more arid plants, so mildew is the more likely culprit.
Mildew is a fungus that thrives in moist environments. It sucks nutrients out of the plant and gradually kills the hibiscus. Spider mites are microscopic bugs that also feed off the plant's nutrients, slowly killing it.
Mildew presents itself as powdery white spots that grow on the surface of the leaves. Spider mite damage removes pigment from the leaf, creating spots of white, gray or yellow discoloration ingrained in the leaf itself. Spider mites also weave small, whitish webs throughout the plant.
Mildew-damaged leaves should be snipped off at the point where they join the stalk. This usually restores plant health, but the book “Pests and Diseases” recommends applying fungicidal spray to the plant to prevent future mildew growth. Combat mite infestations with pesticides or predatory Phytoseiulus mites.