Common Disease Problems

Alternaria Leaf Spot: Small, round reddish brown spots with white to gray centers form on the upper surface of the leaves and along the midrib. The lesions may encircle the stems and cause wilt. This disease is worse in warm, wet or very humid weather. GardenerStar Recommends: Avoid getting water on the foliage. Remove infected plant parts and do not work around wet plants. Provide plenty of air circulation. Contact your Cooperative Extension Service for fungicide recommendations.

Aster Yellows: Plants are stunted, develop witch’s brooms (excessive growth), petals turn green and become deformed. This virus-like condition is caused is spread by leaf hoppers. GardenerStar Recommends: Remove infected plants and control leaf hoppers. Remove weeds in the area.

Botrytis: This fungus causes a grey mold on flowers, leaves, stems and buds. It thrives in cool wet weather conditions. GardenerStar Recommends: Remove affected plant parts, avoid watering at night and getting water on the plant when watering, make sure plants have good air circulation. Contact your Cooperative Extension Service for fungicide recommendations.

Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. GardenerStar Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.

Sclerotinia Crown Rot: Dark spots appear on lower stems and roots, plants wilt and rot. A white fungus with dark structures appear on the dead plant tissue. GardenerStar Recommends: Remove affected plants. Make sure there is good drainage.

Common Pest and Cultural Problems

Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. GardenerStar Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.

Eriophyld Mites: Mites live in the flower buds and cause distortion in the flowers. GardenerStar Recommends: Cut back the plants in fall and remove all plant debris where the mites overwinter.

Leafhoppers: Leafhoppers cause injury to leaves and stunt growth. They also spread disease. GardenerStar Recommends: Remove plant debris. Use insecticidal soaps. Consult your Cooperative Extension Service for other insecticide recommendations.

Japanese Beetles: GardenerStar Recommends: Hand pick early in the morning into a bucket of soapy water.

Plants die over the winter in recommended zones: Wet soils with poor drainage in winter can kill plants. GardenerStar Recommends: Make sure plants are in a well-drained soil. For container grown plants, add one zone colder than your zone when selecting varieties, and keep containers in a protected area outside, mulch heavily.