Pests can damage colorful, fragrant plumeria flowers.Goodshoot/Goodshoot/Getty Images
Frangipani trees (Plumeria spp.) produce the fragrant blooms found in Hawaiian leis. Hardy in U.S. Department of Agriculture plant hardiness zones 9 through 11, they grow up to 25 feet high and 25 feet wide. The oval green leaves measure up to 20 inches long, and the five-petaled flowers are 2 to 4 inches wide. The narrow seed pods grow up to 12 inches long. Species include white-flowered Plumeria alba, and red-blossomed Plumeria rubra. Frangipani prefer well-drained soil and full sun or partial shade, and are susceptible to some pests and diseases .
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Some insects, such as scales and six-spotted spider mites, suck juices from frangipani leaves and stems. Scales measure 1/8- to 1/4-inch long and have a waxy shell, while six-spotted spider mites are barely visible. Damage from these insects includes curled, mottled leaves and premature leaf drop. Spider mites may leave webbing in affected frangipani plants. Remove light infestations with a forceful spray of water or by dabbing the insects with a cotton swab dipped in alcohol. For heavy infestations, spray all plant surfaces with insecticidal soap or a dilution of 2 1/2 tablespoons of horticultural oil in water. Do not apply horticultural oil to drought-stressed frangipani trees.
Caterpillars including cutworms and the Tetrio Sphinx moth caterpillar feed on frangipani plant parts. Cutworms are grayish or yellowish moth larvae that eat and sever leaves, flowers and new stems. A cardboard barrier will protect young plants from cutworms. The Tetrio sphinx moth caterpillar measures up to 6 inches long and has black and yellowish white stripes and a red head and feet. A single caterpillar can eat three frangipani leaves in one day, according to the University of Florida Department of Entomology. Remove Tetrio sphinx caterpillars by hand or spray upper and lower leaf surfaces with 4 teaspoons of Bacillus thuringiensis diluted in 1 gallon of water.
Fungus diseases that affect Frangipani trees include rust and black tip rot. Frangipani rust symptoms include reddish orange or yellow powdery spots on the undersides of frangipani leaves. To prevent new leaves from becoming infected, you must remove, rake up and destroy infected leaves. Spray all plant surfaces with ready-to-use copper fungicide spray when new growth appears in the spring, and repeat the application every seven to 10 days. Black tip fungus occurs in the spring and prevents new growth as it causes branch tips to turn black. In the winter or spring, prune the branch tips back to clean wood to control black tip fungus.
Examples of other frangipani problems include cold temperatures and poor growing conditions. Frangipani trees do not tolerate frost and may lose leaves when the temperature drops below 50 degrees. Drape cloth over the trees during cold weather or plant them in an area protected from north winds. You can bring container-grown frangipani indoors in the winter. The container should hold one gallon for each foot of trunk length, states The Plumeria Society. Poorly drained or waterlogged soil can cause frangipani plants to develop root rot, which interferes with water and nutrient absorption. Symptoms include mushy roots and dull, curled or wilted leaves. Plant in well-drained soil to prevent root rot.