Lilac Blight

• Also commonly known as bacterial blight, lilac blight is a condition most often associated with the lilac tree. This fungus is among the most serious diseases that can affect your tree and can produce wilting of the flowers and foliage, as well as discoloration. You can treat this type of fungus by pruning out the affected stems and burning all infected parts to prevent the fungi from spreading.
  
  

Verticillium Wilt

• Though not nearly as common in lilacs as bacterial blight, verticillium wilt can nonetheless be devastating for your tree. This fungus will cause the flowers to lose their deep purple shade. After losing their color, the flowers will start to wilt. Because there are no known treatments for this type of fungus, you will simply have to remove all infected parts.
  
  

Phytophthora

• Also similar to the lilac blight, the phytophthora blight spreads from the soil and is most common during the cold and wet months of the spring. This fungus forms when hot conditions during the day are followed by cooler and wetter weather at night. This blight will cause brown striping on your leaves in the early stages, and this will lead to fading flower color or wilting. This can commonly occur when your lilac trees are too close to elderberries or to rhododendrons.
  
  

Lilac Mildew

• Though you might associate mildew with your shower tiles, it can also form on your lilac trees. This type of fungus manifests itself on the surface of your lilac leaves and can be especially harmful to the blooms that give the tree its beauty. The fungus will appear as a white and powdery mildew, but can be killed by a simple solution of water and sulfur, as well as other fungicides.