Diseases are always harmful. When lilacs or Syringa shrubs are affected by diseases, it may cause the plants to stop blooming or reduce their number of flowers. In many cases, diseases occurring in the previous year may result in the destruction of the flower buds. In some instances, growers may take preventive or even curative measures. It has often been seen that the lilacs in dry gardens in rural areas are perfectly healthy, while many of those in major cities are vulnerable to a condition known as leaf-roll necrosis. Usually, lilacs grown in places having dry summers and chilly winters are mostly free from diseases compared to those grown in places where the summers are humid and winters are mild. Like diseases, even problems caused by pests like scales and borers may cause the plants to bear fewer blooms. For instance, Syringa vulgaris or the common lilac as well as several of its cultivars are among the lilacs that are very vulnerable to pest invasions.