Jasmine is a warm season plant with small, star-shaped white flowers that emit a powerful sweet fragrance. The plant has glossy, green leaves and may be a shrub or vine. Fungal and bacterial leaf spots can affect the plant and arise from a variety of pests and diseases. However, proper cultivation can resolve most foliar issues.
Sucking insects can cause leaf speckling. If there are tiny spots on the leaves, they are most likely mites. Aphids are slightly larger pests that can be seen on the surface of the leaves. Other insects such as white flies will lay eggs under the plant's leaves, which look like spots. Jasmine isn't prone to insect pests, but it isn't immune to them either. A good shower will usually knock the insects off the plant.
Cercospora Leaf Spot
If the spots are circular, reddish brown and less than half an inch across, the flower may have Cercospora leaf spot. The cause is a fungus that appears when conditions are warm and wet. As the disease progresses, the spots get larger and more irregular. Control the fungus by spraying the flower with a copper fungicide or using the chemicals mancozeb or carbendazim. Remove the infected plant tissue to minimise the spread of the disease. It is not possible to cure the disease, but the spots can be managed.
Alternaria Leaf Blight
Alternaria leaf blight is also a fungal disease that produces brown spots that may eat away at the edges of the leaves. In humid conditions, the fungus reproduces rapidly and will cause blight in a short period. Overhead watering also seems to encourage the spread of the fungus. Basal watering will prevent some of the spread, but water the flower slowly to keep the fungus from splashing up from the soil. Mancozeb or copper oxychloride are also effective controls, but will not cure the fungus.
Jasmine shows stress in a variety of ways. Sometimes its growth is stunted, it wilts or fails to produce new foliage. The leaves can also become discoloured. Fertiliser burns may be the cause of this or it may be too much or too little of something. Jasmine requires full to part sun and regular watering. Drying out may cause the leaves to exhibit discolourations. Jasmine plants do not do well in shade and exposure to cold temperatures for even a short period may cause leaf spotting and burns.