Why Does an Orange Jasmine Lose Its Leaves?

Murraya paniculata, the scientific name for orange jessamine, or orange jasmine, is an evergreen shrub that grows between 8 and 12 feet tall. It has glossy, dark-green leaves and produces clusters of fragrant, star-shaped white flowers that smell like orange blossoms; this shrub is also known as mock orange. Orange jessamine isn't prone to any serious diseases or insect pests, but there are a few problems that can cause leaf drop.

Bacterial blight causes water-soaked spots to appear on the leaves. The spots may be surrounded by a yellow halo and will later turn dark brown or black. As the disease progresses, the spots may merge, causing the entire leaf to look blighted; the stems may develop black lesions. In addition, the buds may turn black while flowers turn limp and brown. Leaves become distorted and drop from the shrub, and shoots may die. Control bacterial blight by pruning infected shoots and leaves and destroying them. This bacteria thrives in cool, wet conditions. Avoid overhead watering and don't crowd plants. Bacterial blight can also be controlled chemically with fixed copper, a type of fungicide that is less harmful to plant tissue than another common copper fungicide called Bordeaux mixture.

Septoria is a fungal disease that causes reddish-brown spots to appear on plant leaves. The spots are surrounded by a yellow halo and may merge with other spots to form large blotches. Shrubs may suffer premature leaf drop. Copper fungicides, which are available from garden supply stores, can be used in the spring, after leaf-out, as a protectant. Avoid watering shrubs from overhead, to reduce problems with Septoria. Remove infected leaves and twigs. Avoid overfertilization because it encourages new growth, which is more susceptible to disease.

Coniothyrium is a fungal disease that causes irregular brown or grayish-brown spots to form on leaves. Spots may have a dark border and small black specks, which are fungal-fruiting bodies and form inside older spots. In severe cases, the leaves may yellow and drop. Leaf spots are usually a cosmetic problem, but when shrubs are attacked several years in a row, they can become weakened and prone to other diseases. Control Coniothyrium by removing diseased leaves. Don't water shrubs from overhead. Apply copper fungicides to help keep this disease from spreading.

Citrus leafminer larvae are minute greenish-yellow caterpillars that are only about 1/10 inch long. They're found inside the leaves of host plants, including the orange jessamine bush. As the caterpillars feed inside the leaves, they form serpentine tunnels or "mines" that are filled with tiny black specks of frass, or excrement. The frass appears as a thin, dark line. Other symptoms of leafminer infestation include crumpled and curled leaves and defoliation of young trees. Many insecticides aren't effective against leafminers since they're protected inside the leaves. Natural insecticides that contain azadirachtin or spinosad may help, and they won't hurt beneficial insects. However, they have to be reapplied every week or so. Parasitical wasps and other natural enemies are very effective in reducing leafminer populations. In addition, leafminer populations drop when summer temperatures become hot.