They are susceptible to powdery mildew, and a pesky insect, the lilac-ash borer, finds the plant as appealing as the pollinators do. If you live in regions that are often too warm for lilacs ...

Monitor lilac bushes regularly for pests like aphids, scales, and borers. Neem oil or insecticidal soap can be effective treatments. Keeping the area around the bushes clean can prevent infestations.