What Is A Good Insect Spray For Hibiscus Plants?

Tropical hibiscus (Hibiscus rosa-sinensis) puts on a show with big, bright flowers that make any gardener smile. Unfortunately, bugs love it too.

More on Hibiscus tree care.

Aphids, whiteflies and mealybugs suck the juices from leaves and buds, and nobody wants a Hibiscus with yellow leaves, cupped or malformed leaves. So which spray actually helps without hurting the plant, you, or the good bugs?

Here’s what university extension experts recommend, and the sprays to leave on the shelf.

What’s A Good Insect Spray for Hibiscus?

The short answer: start with plain water. The University of California Statewide IPM Program (UC IPM) says a strong spray of water knocks aphids off sturdy plants, that most dislodged aphids won’t be able to return, and that the spray washes off their sticky honeydew too. Do it early in the day so the plant dries off quickly in the sun and is less likely to get fungal diseases.

When water isn’t enough, reach for an insecticidal soap or an oil spray. Aphids, whiteflies and mealybugs on hibiscus, caught early, are easily controlled with insecticidal soaps or horticultural oils. Soaps and oils are the best choices for most aphid situations, and plant-derived oils such as neem count among them.

Not every product on the shelf is a good pick, though, and kitchen mixes are a different story (more on that below).

Which Pests Are You Spraying?

Hibiscus attracts soft-bodied, juice-sucking pests like aphids (plant lice), pink hibiscus mealybugs, spider mites, Hibiscus thrips and whiteflies.

• Aphids, whiteflies and mealybugs: These piercing-sucking insects are usually found in clusters on hibiscus leaves and flower buds. Scout by flipping the leaves, or watch for black sooty mold growing on the honeydew they leave behind.
• Pink hibiscus mealybug: This pest injects a toxic saliva that curls and contorts leaves. On hibiscus it usually infests young twigs, leaving deformed tips, shortened growth between leaves and thickened twigs. Buds may not flower, and very high numbers can kill plants.
• Whiteflies: Hibiscus is among the host plants of both the sweetpotato whitefly and the giant whitefly.
• Hardy hibiscus too: Aphids, whiteflies and Japanese beetles are insect pests of hardy species such as Hibiscus moscheutos as well as tropical hibiscus.

Insecticidal soaps and oils both help control these Hibiscus plant pests. Soaps and oils control a wide range of soft-bodied pests, including aphids, mealybugs, mites, scales, thrips and whiteflies.

How Do Soap and Oil Sprays Work?

Both are contact sprays: they only work on the bugs they actually hit.

• Insecticidal soaps: They kill by damaging an insect’s protective outer coating, causing it to dry out.
• Oils: Oils can block insects’ breathing holes and suffocate them, and the fatty acids in plant oils may disrupt cell membranes. Oils are most effective against small, soft-bodied insects and mites that sit still or move slowly, such as aphids, scales and whiteflies.
• No lasting effect: Soaps, neem oil and horticultural oil kill only the aphids present on the day you spray, so you may need to repeat. They leave no toxic residue, so they don’t kill natural enemies that move in after the spray.

That cuts both ways. These sprays can kill some natural enemies that are on the plant and hit by the spray, and even insecticidal soaps damage pest and beneficial insects alike. Look for lady beetles and other good guys before you spray.

What About Neem Oil?

Neem oil comes from the seeds of the neem tree. The National Pesticide Information Center (NPIC) calls it a naturally occurring pesticide, and says its most active component, azadirachtin, reduces insect feeding, acts as a repellent and interferes with insect hormones, making it harder for insects to grow and lay eggs.

Neem oil products are commonly used to control aphids, whiteflies, mites, scale crawlers, thrips and other soft-bodied insects. Neem is most effective against actively growing, immature insects.

Is it safe for bees? Neem oil is practically non-toxic to birds, mammals, bees and plants, and insects must eat the treated plant to be killed, so bees and other pollinators are not likely to be harmed. Even so, the EPA says neem product labels direct users not to apply when honeybees are actively visiting flowers in the area. Hibiscus is often in bloom, so spray when bees aren’t working the flowers and follow the label.

A few more cautions: neem oil can be slightly irritating to the eyes and skin, it is slightly toxic to fish, and cats treated with neem products for fleas in other countries have had adverse reactions. Azadirachtin also breaks down on plant leaves fast, with a half-life of 1 to 2.5 days. More on Neem pesticide oil.

Where Can You Buy Insecticidal Soap or Neem Oil Sprays?

Insecticidal soaps can be found where garden supplies are sold, either as a concentrate you dilute or as a ready-to-use spray bottle.

Read the label before you buy. Soaps made for use as pesticides are registered as insecticidal soaps, with labels that give directions for use, precautions and the plant species that are sensitive to the product. Registered insecticidal soaps are usually only 1 to 2% soap by volume. Mix any concentrate exactly as its label directs, and check that hibiscus or ornamentals are listed.

What About Homemade Sprays for Hibiscus?

Kitchen-sink recipes are everywhere online, but extension experts say skip them:

• Dish soap isn’t really soap. Dish “soaps” are detergents, and even watered down, detergents cut through the waxy layer that protects leaves, often leaving damaged, dry, crispy leaves.
• Homemade soap recipes injure plants more often. Homemade soap recipes are not recommended because they are more likely to injure plants, while commercial insecticidal soaps are tested on plants.
• They haven’t been tested. Kitchen mixes (dish soap, vinegar, garlic, cooking oils and the like) generally haven’t been studied in replicated research trials, and their effects on natural enemies, pollinators and people haven’t been proven safe; see this statement on homemade pesticides.
• Some ingredients burn leaves. Vinegar and alcohol are phytotoxic, causing leaf burn and other plant injury, and mixing different cleaning products can be toxic to people.

Like the idea of plant-based ingredients? Many commercial insecticides combine plant oils and herbal extracts such as rosemary, peppermint, thyme and clove. If you like that idea, buy one of those commercial products and follow its label rather than mixing a homemade brew.

Check Out These Other Hibiscus Articles:

• Fertilizer For Hibiscus
• Growing Hibiscus Moscheutos

What About Stronger Chemical Sprays?

NOTE: A spray may say it kills a pest; that doesn’t mean it’s good for your Hibiscus or the environment.

• Malathion: don’t. UF/IFAS says to read labels carefully because you should never use the pesticide malathion on hibiscus.
• Malathion, permethrin and acephate: These foliar sprays (acephate on nonfood plants only) may kill more aphids than soaps and oils, but their use should be limited because they also kill the natural enemies that provide long-term control and are associated with bee kills and environmental problems.
• Broad-spectrum sprays and whiteflies: For whiteflies, avoid broad-spectrum pesticides such as pyrethroids, organophosphates and neonicotinoids, and choose products least harmful to natural enemies, such as insecticidal soaps and oils.
• Systemic insecticides: Systemics such as imidacloprid can harm predators, parasitoids and pollinators, and should not be applied to plants in bloom or prior to bloom. Hibiscus blooms over a long season, nearly year-round in South Florida.

Got kids or pets? Oils and soaps are also safer to use when children and pets may be present. Keep everyone out of the spray, and follow the label.

How Should You Apply Oil Or Soap Sprays?

Timing matters as much as the product. Clemson Extension says soaps and oils can damage plants when they’re applied under the wrong conditions.

When To Spray

• Early morning or late evening. This slows drying and improves effectiveness.
• Not in heat or direct sun. Don’t apply when temperatures are above 90°F or in direct sunlight; plants in heat above 90°F should never be treated with soaps.
• Not on a thirsty plant. Don’t spray plants under water or drought stress.
• Watch the humidity. High humidity, which slows drying, is among the conditions that can lead to plant damage, and plants in excessive humidity should never be treated with soaps.

How To Spray

• Test first. Spray a small area and wait 24 hours to see if any damage shows up.
• Check your water. Hard water makes insecticidal soap less effective. Mix the soap at its label rate in a glass jar, shake it and let it stand 15 minutes: a uniform, milky mix is fine, but scum on top means you should use distilled or bottled water.
• Cover everything. The spray must cover the pests directly, so wet the upper and lower leaf surfaces and the stems. Many pests are found on the undersides of the leaves.
• Repeat as the label directs. Repeat applications may be needed because soaps and oils don’t give long-lasting control, but avoid excessive applications, since leaf damage can build up with repeated exposure.
• Rinse if it wilts. Rinse plants with clean water if they wilt or the leaf edges turn brown within a few hours of treatment.

Which pest gives your hibiscus the most trouble? Tell us what’s worked for you!