Why Do My Cosmos Flowers Look Unhealthy?

Do the stems break off easily?

Are the leaves, stems, and buds distorted?

Are the flower buds dying, petals are distorted and growth stunted?

Are the leaves discolored and distorted?

Are the leaves greenish-yellow, and the growth is poor?

Does the plant wilts suddenly?

Are the leaves of your cosmos flower covered with white powder?

Does the plant wilts and, leaves and stems are discolored?

Stalk borers are long, thin, striped caterpillars that eat their way through cosmos stalk centers. Small, round stem holes may betray their presence. Once plants are visibly affected, there is no cure. If borers are a regular problem, spray plants with BTK early in the season as borers enter plants.

Distorted leaves, stems and buds are caused by aphids. These tiny insects can vary in color, green, pink, black, gray to completely white. They 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.

Dying flower buds, distorted petals, and stunted growth are caused by thrips. Thrips are tiny, yellow to black flying insects. They hide under leaves and inside flowers. Severely infested plant parts should be pruned off and destroyed. Control thrips by introducing lady beetles or lacewings, their natural predators. Insecticidal soap helps in severe infestations.

Discolored and distorted leaves are caused by leafhoppers. These small, green or brown insects feed by sucking juices from leaves undersides. Leafhoppers may be the carriers of Aster yellows disease, so it is important to keep them in control. Insecticidal soap helps with severe infestations.

Greenish yellow leaves followed by a poor growth is caused by Aster yellows disease. This disease is transferred by insects leafhoppers. There is no cure for Aster yellows, so the affected plants should be destroyed. Prevent the disease by controlling leafhoppers. Spray the plants with the insecticidal soap 3 times, once every 3 days.

Bacterial wilt causes a soft rot at the base of the stem, killing plants quickly. Remove and destroy infected plants. Do not replant the cosmos in that area.

White, powdery patches on the leaves are caused by a fungus Powdery mildew. Powdery mildew usually appears in damp places. Encourage good air circulation around the affected plants by thining 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.

These symptoms are most likely caused by Fusarium wilt. There is no cure for Fusarium wilt, so the infected plants should be destroyed. Do not plant new cosmos flowers or any susceptible plants to Fusarium wilt in the same spot for several years.

Some environmental issues or poor growing conditions may have caused your cosmos flowers to look unhealthy. These flowers prefer full sun and light, average soil kept slightly on the dry side. Avoid overwatering, and do not fertilize.