What Is Wrong With The Yarrow In My Garden?

Do the leaves and flowers have dead gray blotches?

Are the leaves covered with white powder?

Do the leaves have moist or brown spots on them?

Are the leaves yellow and wilting, stems blackened at the base and the plant is toppling over?

Is there a sticky foam, resembling spit on the plants?

Are the leaves pale on their upper side and are there any dusty blisters on the undersides?

Dead blotches on leaves and flowers indicate a fungal disease - Botrytis blight. You can prevent Botrytis blight disease by planting flowers in areas with good air circulation. Water plants sparsely. Heavily infected plants should be removed. Spray weekly with a copper fungicide until the disease is under control.

White, powdery patches on the leaves are caused by a fungal disease Powdery mildew. Powdery mildew usually appears in damp places. Encourage good air circulation around the affected plants by thining them and any surrounding plants. Water plants from bellow to keep foliage dry. Any affected leaves should be cut off and removed. Any commercial fungicidal spray will protect your plant from further infections.

Your plants might be suffering from Anthracnose or some other fungal leaf spot. Spots may enlarge rapidly, especially in wet weather. Destroy infected leaves or plants. Spray plants with sulfur to prevent the disease from spreading, especially if the weather is wet. Prevent problems by thinning plants to provide good air circulation.

Stem rot causes these symptoms in yarrow. These problems are common when plants are kept overly wet or are grown in poorly drained soil. Remove and destroy infected plants and surrounding soil. Let the soil dry somewhat between waterings, and incorporate organic matter to improve soil drainage. Avoid overwatering and overcrowding.

Spittlebugs will sometimes attack yarrow. The insect produces a protective foam that looks like spit. The foam helps protect the insect from ultraviolet light, predators, and insecticides. Use a strong spray of water to wash the foam away. The resulting exposure to UV light will kill the insect and expose it to predators. A stronger spray of water may also remove the insect from the plant.

Likely cause for these symptoms is a fungal disease - Rust. Provide good air circulation around plants by thining them. Avoid making leaves wet when watering. All infected leaves should be removed. Spray leaves with sulfur early in the season to prevent rust or to treat mild infections.

If the leaves are distorted and curled the culprits are aphids. These tiny insects cluster under leaves and on growing tips where they feed on plant sap. Leaves, stems, and buds get distorted, and later leaves and flowers drop from the plant. You can control them by washing them off the plant with water spray. Insecticidal soap should be used with severe infestations.