Ligustrum is also known as privet and is common as a hedge in the home landscape. The plant has stiff, glossy leaves and an attractive, tight growth habit. Ligustrum are easy to grow and respond well to heavy pruning. There are several types of privet native to Europe, North Africa and Asia. Ligustrum has few pest problems and only a couple of fungal and bacterial disease challenges. It is fast growing and forms a dense and compact border.
Many fungal diseases affect plants. Fungi need moisture to thrive and they reproduce by spores. The spores can be transported anywhere in the air or in water; once they find a hospitable area, they bloom. The leaf spots on the Ligustrum are from a very common fungal pest that is often found on this shrub. It causes necrotic areas in the leaves. The spots begin as yellowing areas and progress to brown. The disfigurement is found on the edges of the leaves and then migrates to the centre.
Cercospora leaf spot is the pathogen responsible for the plant's distress. It is an equal-opportunity pest found on vegetable plants, grasses, ornamentals and almost any other type of plant. In other species it can affect not only the leaves but also the fruit, flower, stem, pods and seeds. The fungus is most prevalent when temperatures are warm but there is adequate moisture. Poor drainage, crowded plants and diseased material left on the ground contribute to the spread of the disease.
Cercospora leaf spot will cause the leaves that are affected to fall off. In years with the ideal weather conditions and where no control is attempted, the disease can nearly defoliate the Ligustrum. Plants rely upon their leaves to perform photosynthesis, which turns the sun's energy into usable plant sugars. Without an adequate number of leaves, the plant essentially starves and loses vigour. The fungal disease will not kill the plant outright, but the loss of vigour makes the Ligustrum less able to withstand any other stresses. The combination of problems could kill the privet.
There is no control for Cercospora. The first step in management is to rake. The spores are on the dropped leaves and will overwinter and spread the following spring. All debris under and around the tree needs to be removed. A biannual application of an appropriate fungicide can minimise the disease. The fungicide needs to go on before there is evidence of a problem, preferably in earliest spring for the first application. Myclobutanil and Azoxystrobin are two active ingredients that are recommended by Clemson University.