When to Apply Copper Sulfate to Lilac Trees?

Lilac Blight

• Lilac blight is a fungal disease that affects many lilac shrubs, particularly in the early spring. If your lilac is not a blight-resistant variety, it can contract this disease when fluctuations in spring temperatures are paired with cold rains. The disease appears as blotches on the leaves that turn brown and wilt, and as brown spots on the stems and leaves of young shoots. In addition, when infection is present, lilac buds may not open or may turn black and die. Lilac blight symptoms are similar to those of overwinter damage; they appear on the plant as brown or black spots, dead leaves and problematic blooms.

How Copper Sulfate Works

• You can use copper sulfate as a fungicide for disease treatment or as a disease preventative. It functions as a fungicide by binding to fungal proteins present on the plant and damaging the fungal cells. The cell damage causes the fungus to leak and then die. Copper sulfate does not move into the plant tissues when you apply it to the plant, but rather provides an exterior barrier that prevents the fungus from entering the plant. This exterior barrier gives copper sulfate its disease preventative properties.

Applying Copper Sulfate

• Apply copper sulfate to lilac bushes twice a year: once prior to the fall rains, and again in the spring before the bush buds. Lilac blight can overwinter; therefore, applying copper sulfate in the fall and the spring helps to prevent blight infections. Do not apply copper sulfate when temperatures are above 80 degrees Fahrenheit, or when the bush is blooming. Copper sensitivity can damage young foliage, therefore do not use copper sulfate as a season-long fungicide. Treatment only in the fall and spring prevents and treats lilac blight without damaging tender growth.

Special Considerations

• Copper sulfate can cause phototoxicity in lilac bushes, which renders them susceptible to sun damage and can ultimately kill the plant. Never apply copper sulfate to a plant that is already in bloom or with young, tender new growth as damage to the plant can occur. In addition, make sure you properly diagnose the plant problem or disease before using copper sulfate for treatment.