Symptoms: The sudden death of flowers, buds, leaves, young fruits and succulent shoots characterizes a blight disease. The blighted leaves, fruits and flowers are black and shriveled and look as though they were scorched with fire. They remain clinging to the shoots. Shoots often have a bent, drooped tip resembling a shepherd's crook.
Cause: Bacteria generally cause blights during wet weather in early spring when buds are breaking. Cool spring temperatures favor some blights and warm temperatures favor others. Fire blight of crabapples, for example, is favored by warm springs, and bacterial blight of lilac is favored by cool springs. In wet spring weather, cankers formed during previous infections ooze droplets of bacteria. The bacteria are splashed by rain and blown about as mists, or insects may visit the attractive ooze and carry it about. Infection usually begins either through nectaries of flowers or through the microscopic breathing holes (stomates) in leaves. In lilac bacterial blight, typical blight symptoms may occur on new growth. When infection occurs later in spring when leaves are more mature, the bacteria cause a leaf spotting disease.
Control: Avoid using high nitrogen fertilizers on susceptible cultivars. Only fungicides containing copper may be effective against bacterial blights and bacterial disease, but copper may burn foliage on some cultivars.