If your lilacs are looking rough this summer, you’re not alone. The likely culprit? Lilac leaf spot, a relatively new fungal disease in Minnesota.

Thought to be caused by Pseudocercospora or Septoria fungi, lilac leaf spot has been quietly spreading across the Midwest. It mainly affects common lilacs ( Syringa vulgaris ), though Japanese tree lilacs ( S. reticulata ) can also be infected.

While not usually fatal, the disease can cause heavy leaf loss and stress, even in mature plants that have never had issues before.

Spotting the symptoms

Symptoms typically appear from July to September. Leaves turn yellow, then develop brown, blocky spots that grow and merge. Affected leaves often twist, curl, and drop early.

The fungus thrives in warm, humid weather, especially when tem

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