Pittosporums (Pittosporum spp.), hardy in U.S. Department of Agriculture plant hardiness zones 7 through 10, are evergreen shrubs used as accent shrubs, hedges, or for greenery in floral arrangements. They can reach 8 to 12 feet in height and 4 to 8 feet wide. The foliage is lustrous and dark green, and their white flowers are often fragrant. The most common pittosporum in nurseries is the Pittosporum tobira, also known as Japanese pittosporum or Japanese mockorange, and its cultivars.
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Leaf diseases are usually caused by fungi and result in leaves becoming unsightly. Most can be avoided with preventative applications of fungicide labeled for pittosporum. Angular leaf spot produces light yellow to tan spots on the upper leaf surface. Alternaria leaf spot looks similar in the early stages, then lesions develop necrotic centers and may appear crinkled. Rhizoctonia aerial blight creates small, tan, irregular spots that are sometimes surrounded by a purple halo. Leaves may curl up into a cylinder, and may become matted with a threadlike fungus. Most fungal diseases enter in through an injury on the plant.
Rough bark disease is caused by a virus. It creates roughened bark on both trunks and stems. The infected area may be elevated above the normal bark level, and this infected bark may girdle stems and trunks, limiting movement of nutrients past the infected section. Other symptoms include death or distortion above the infected areas and general stunting of the plant. There is no cure for the disease, and the pittosporum may eventually need to be removed.
Stem or Branch Diseases
Fungal diseases affecting stems and branches usually attack shrubs through an injury and may be prevented through regular fungicide applications. However, once these diseases have begun there is little that can be done aside from trimming off infected areas as they appear. Corticum limb blight symptoms include a pinkish-orange stain around the infected area. Wilting may result, and if the infection becomes severe the pittosporum may die. Southern blight produces rotting stems that inhibit fluid movement, and foliage may wilt and die. A white substance may appear near the soil line. The fungus may remain in the soil after the plant has died.
Root diseases may not be recognized until it's too late. Little can be done once the pittosporum is infected. Mushroom root rot infects the roots and the trunks at the soil level, girdling the plant and stopping the flow of fluids. Roots may display a white coating, and mushrooms may appear late in the disease cycle. The fungus remains in the soil after the plant has died. Cotton root rot produces bare roots with their outer bark decayed, so the roots cannot take in fluids. Pythium root rot produces black and soggy roots with no feeder roots. Leaves may fall suddenly or over a period of time.