Plumeria rubra and Plumeria obtusa, also called frangipani, are small tropical flowering trees belonging in the Apocynaceae family. It is well adapted to outdoor growth in frost-free regions of the United States. The tropical American native is a hardy and low-maintenance addition to the landscape. Pest and disease infestation are rarely problematic, according to The Plumeria Society of America. If problems do occur, gardeners have a variety of treatment options.
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Plumeria tolerates a variety of soils that have good drainage, including sand, loam or clay. The plant tolerates growing in alkaline or acidic soils. It does not tolerate growing in soils that retain water or are consistently wet. When planted in saturated sites, the plant develops the fatal condition of root rot. When the roots grow constantly in wet environments, root rot develops. The disease usually starts showing its effects at the plant’s base. The trunk begins collapsing and slowly dies, enveloping the tree from the bottom up. Avoid root rot by planting plumeria in areas with good drainage and not overwatering. If the disease is severe, prune the unaffected portion of the plant from the infected trunk. Allow the cut end to heal over for approximately one week and replant in a well-drained location.
Even plumeria grown in optimal conditions may eventually develop rust (Coleosporium domingense). It is a common fungus found on plumeria leaves. The rust shows itself as tiny, brownish-red spots dotting foliage undersides. In most instances, gardeners can ignore the problem, as small infestations do not affect the plumeria’s health, according to the College of Tropical Agriculture and Human Resources. If the rust is severe, covering the majority of the plant’s foliage and causing leaf drop, treat the problem with a broad-spectrum fungicide. Apply according to the label instructions. Prune off severely infected foliage and discard in a plastic bag.
Proper planting is essential to prevent powdery mildew infestations. The tree sometimes grows over 25 feet tall and wide. Place the plant in a location where it is not crowded by other vegetation or structures. The fungus develops with improper air circulation. Powdery mildew shows up on the plumeria’s foliage as a white, hairy mold. Severe infestations sometimes cause the plant’s decline. Spray the plumeria with a broad-spectrum fungicide, following instructions. Create more air circulation around the tree, so the plant is less susceptible to infection.
Sooty mold is seldom deadly and usually just leaves the plumeria looking unattractive . The fungus appears on the foliage as a black mold. First, treat the pests creating the problem, as the mold attaches itself to secretions of insect honeydew. Aphids, thrips and whitefly insects are usually present when sooty mold occurs. Spray the plumeria with a strong spray of water to dislodge the pests from the plant. Kill the pests by using an insecticidal soap or Malathion, as recommended by The Plumeria Society of America. Use the insecticidal product following label instructions. Wash the plumeria foliage with a mild solution of dish soap and water, to remove the black fungus.