Blighting of new shoots is black in color, starting as spots on leaves and branches which rapidly involve the entire shoot. Bacteria may be found in abundance in diseased tissues, including the wood. Many newer varieties are resistant to infection. Leaves show what looks like a nutritional trouble. Areas between veins become light green or yellow, and margins turn brown or are flecked with necrotic spots.
Leaves are smaller, and growth is slower.
This blight occurs when lilac scions are grafted onto privet stock. After a time an incompatibility between stock and scion shows up. If the lilac can make some of its own roots, the trouble may be overcome in time. Insect Problems Lilac borer, Podosesia syringae . The larva bores into the stems of lilac and privet.