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Plant NameTypeDescription 
Bacterial blightLilacDiseaseBacterial blight starts as brown spots on leaves and stems in the early spring. These spots become black with age and cause death of leaves and young shoots, which may bend over at the infection site. Infected older shoots show dying leaves as the infection enlarges along the stem. Flower clusters may also be affected. Infection often occurs on weakened or unhealthy plants and at injury sites such as those caused by wounds and frost damage. Pears, blueberries, cherry, maple, and many other woody plants can also be infected by this blight.
Powdery mildewLilacDiseasePowdery mildew is a fungal disease of the leaves. On lilac, it shows typical powdery gray-white growth on the upper leaf surface. Powdery mildew usually occurs fairly late in the season, and does relatively little damage to the plants. This disease is worse in summers with little rainfall and high amounts of fog or cloud cover.
Lilac borerLilacInsectThe lilac borer, also known as the ash borer, is a member of the clearwing moth family. The adults of many clearwing moths mimic yellowjackets or paper wasps. The larvae of this moth cause damage to lilac, ash, and privet. The larvae tunnel in the bark of stems (trunk) and branches causing a gradual weakening of the plant. Other than emergence holes, one can determine the pests' presence by the pupal skeletons attached to the bark at the emergence sites. There is usually only one generation per year. However, a two-year cycle can occur in the northern part of its range. Adult numbers usually peak in May or June and females lay their eggs singly in bark crevices where they soon hatch and burrow their way into the phloem tissue and continue feeding. Emerging full-grown larvae produce a round hole about 1/16 inch in diameter. Urban, open grown trees are highly susceptible to infestation.
Lilac leafminerLilacInsectLeafminers feed by removing green tissue from between the upper and lower surfaces of the leaves. Symptoms of feeding by the green larvae include large brown blotches which may distort the leaves. The adult lilac leafminer is a small brown moth. The lilac leafminer may also infest privet.
Oystershell scaleLilacInsectOystershell scale insects are usually found on trunks, branches, and twigs. They occur less frequently on the leaves and other plant parts. The mature scale is approximately 1/8" long, striped with grayish and brown bands, and elongated like an oyster or mussel shell. Infested plants may wilt or show off-color foliage. Scales can be spread from plant to plant by birds, people, wind, or insects.