Privet hedges are extremely hardy and can thrive in almost any soil condition or location. However, that doesn't mean privet hedges are immune to disease.
The two most common privet hedge diseases are wilt and honey fungus.
Wilt, which is a form of fungus, causes privet hedge leaves to curl, turn yellow or reddish, and die. Honey fungus can cause root rot and various other problems, resulting in leaves failing to appear in spring, or full leafy branches dying off.
Peeling away bark to reveal wood discoloration and striping will confirm wilt. Honey fungus produces strands that look like black boot laces, as well as yellow mushrooms and cream-colored fungi along the plant's base.
To treat wilt, use fertilizer low in nitrogen and high in potassium. Be sure to sterilize all pruning tools. If the plant cannot be saved, remove it with the root ball intact and never replant privet in the same hole. Privet hedges infected with honey fungus should be dug up and removed.
Using a clean wood mulch and well-drained soil will help prevent honey fungus. The best way to prevent wilt is to only plant varieties of privet resistant to the fungus.
Spider mites may also infest and kill privet hedges. Applying pesticides or introducing some of their natural predators, such as ladybugs, can control spider mites.