Lilac bushes are fairly disease resistant and one of the hardiest plants around. Some grow into magnificent bushes and trees with hundreds of blooms even after years of neglect. I have seen old, abandoned farm houses where the building is collapsing from years of disuse and beside it, a plump, tall lilac bush cover in delicate purple blooms.
To survive so long without care is a testament to their disease resistance but it doesn’t mean they are disease-free. There are a few diseases that can affect your lilac bush. Recognizing the signs and knowing what to do gives you the arsenal you need to combat disease in your lilac bush.
Blight is a disease that affects many types of plants. Symptoms in lilacs are recognized by blackened buds and leaves which appear scorched. Symptoms typically appear following a winter injury, late frost or a particularly wet spring. The only treatment for lilac blight is to prune out damaged branches. Cut about six inches below the infection site. Clean pruning tools between cuts in a solution of water and 10% bleach to prevent spreading the disease. Destroy all infected branches.
The best way to control Lilac blight is through prevention. Bushes should be planted with plenty of space around them and pruned annually to allow plenty of air flow through the bush. Do not over fertilize or add fertilizer in the fall. A light coating of copper sulfate in the spring before buds appear can also help.
This fungus appears as a white or gray coating on leaves, flowers and branches. In some cases the leaves might start to curl before the fungus is visible. In severe cases, the leaves will begin to drop prematurely. Outbreaks generally occur when temperatures are between 60 an 80 degrees and conditions are damp. The only treatment is to remove and destroy infected branches. Prevention involves annual pruning to provide good air flow and removing fallen leaves that can harbor the disease.
Virus Ring Spot and Mosaic virus are the most common viruses to affect lilacs. Virus ring spot can be recognized by yellow spots on leaves which eventually turn completely yellow causing the leaf to fall off. Mosaic virus causes a yellow-green mottled appearance. Both viruses are fatal and plants should be destroyed to prevent the spread of disease. They attack plants that are already weakened or damaged. They are spread by insects like aphids and grasshoppers. Insecticides that control these pests may help.