- Healthy hibiscus plants have a greater chance of warding off and overcoming pests than stressed plants. In general, grow your hibiscus tree in areas of the garden that allow for full sunlight for best growth, blossoming and flower color. Most hibiscus plants thrive in moist, well-drained soil. Maintain a soil pH of 5.5 to 6.5 and avoid the alkaline soil conditions that lead to health problems. However, determine which hibiscus species and variety you are growing, as requirements vary between them. Irrigate hibiscus trees to keep soil moist without creating waterlogged conditions. Apply approximately 12 to 18 inches of water weekly when natural rainfall is not sufficient.
- Sucking and chewing pests attack hibiscus plants. Whiteflies, for example, are pests that suck tissue fluid from tender plant growth. Look for whiteflies underneath leaves, where they commonly gather en masse. Hibiscus is particularly susceptible to giant whiteflies -- Aleurodicus dugesii -- pests that are approximately 0.2 inches in length. Whiteflies have yellow bodies and white wings.
Check your plants for chewing pests, such as Fuller rose beetles, which target hibiscus plants among other plants, such as azaleas and citrus plants. Look for beetles displaying bodies measuring approximately 1/3 inch in length with brown-grey bodies, curved snouts and bulging eyes. - Whiteflies on hibiscus trees typically cause the most damage during warmer weather. As they feed on tissue fluid, they cause a secondary problem when they release honeydew, a sticky substance that drips onto other hibiscus plant parts. This substance promotes the development of sooty mold, a dark, near-black fungal growth that covers plant parts. This mold cover blocks out sunlight necessary for the plant's function and growth. In addition, ants often show up to feed on this sweet substance. Feeding alone results in the yellowing of leaves, which often drop to the ground.
Fuller rose beetles chew on leaves and flowers. Look for foliage with a "notched or ragged" appearance, notes UC IPM Online. Beetles can eat entire leaves, leading to a bare plant and diminished plant health. In their immature larval form, these pests chew on hibiscus roots, but do not cause damage as severe as adults. - To control whitefly problems on hibiscus trees, remove and destroy affected plant parts to decrease pest population and spread. Release natural enemies like minute pirate bugs onto your plants, as they will kill whiteflies without hurting your plants. Buy natural enemies in garden supply stores. While insecticides typically provide only minimal control and will also kill natural enemies, for severe problems, apply insecticidal soap.
To control Fuller rose beetles on hibiscus plants, trim back any plant parts that droop and touch other plants or the ground. Release natural enemies like parasitic wasps. Contact your local county extension agent for appropriate pesticides if the infestation is severe, as hibiscus plants are sensitive to chemicals.
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