Common Disease Problems
Bacterial Blight: This usually only occurs on young plants in warm weather. Small oozing cankers appear on the branches and buds. Cankers may continue to completely encircle infected branches, eventually killing them. Burpee Recommends: Practice good garden hygiene at the end of the season and discard, do not compost, possibly diseased plants and plant parts. Space plants to allow for adequate air circulation. Prune all infected branches below cankers. Contact your Cooperative Extension Service for recommendations.
Bacterial Leaf Spot: First signs are small translucent spots with a broad yellowish edge that slowly enlarge and become angular or irregularly circular with a reddish center. It thrives in cooler temperatures. The disease may also affect and disfigure flower heads. Burpee Recommends: Remove infected plants. Avoid overhead watering. Do not work around plants when they are wet.
Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations. Some lilac varieties are resistant.
Common Pest and Cultural Problems
Lilac Leafminers: These insects bore just under the leaf surface causing irregular serpentine lines. The larvae are yellow cylindrical maggots and the adults are small black and yellow flies. They do not usually kill plants, but disfigure the foliage. Burpee Recommends: Remove affected foliage. Sanitation is important so be sure to remove all debris at the end of the season.
Scale: Small bugs look like brown, black, gray to white bumps on the stems of plants. Scale may not have any apparent legs and may not move. Scales have a sucking mouth part. Scale may produce honeydew so leaves and stems may be sticky. Scale can weaken the plant causing it to grow very slowly and it may wilt at the middle of the day. Burpee Recommends: Completely spray the stems with insecticidal soap. For a severe infestation contact your local County Extension Service for recommendations for your area.
Spider Mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.
Do I need to prune my lilac? If so, when? Pruning is only needed if the plant is getting too large or if some of the branches are not producing freely. Prune right after it has finished flowering.
Are lilacs good for cut flowers? Yes, they make great cut flowers and are very fragrant.
Do lilacs do well in an acid soil? No, lilac needs a neutral soil. If your soil is acidic add lime to raise the pH.
Can I grow any lilacs in a container? Smaller varieties are now available and may be planted in larger containers. Be sure to use a commercial potting mix.