My Coneflowers Are Dying

Bacterial Infections

• The incidence of coneflowers contracting a bacterial disease is slim, but it does happen and it can kill the plant. Most bacterial diseases manifest themselves with spots on the flowers and leaves. These spots grow larger with time. Septoria starts at the leaves near the bottom of the plant and works its way up. Cercospara appears when weather is very hot and humid. Xanthomonas campestris causes blotches that have a yellow, translucent ring around the edge of the spot.

Fungal Infections

• Fungus is rare on coneflowers, yet the plant can be killed by an extensive infection. A fungal infection causes spots on leaves and usually prevents blooms from looking their best. Botrytis cinerea creates a gray moldy substance that appears all over the flowers, usually during humid periods. Bacterial and fungal infections stay in the leaves and stems of the flower over winter and come back the next year if the plant survives. Control them by removing the dead material after the growth period has ended and destroy it. Avoid overhead watering during the summer that can cause excess water to stay on leaves and stems, inviting fungus to attach. Space plants several feet apart to ensure good air circulation and the infections probably will not become a problem.

Other Diseases

• Aster yellow is a disease carried by the aster leafhopper. The insects are greenish-yellow and have a small wedge-shaped body. They carry a microorganism that invades the tissue of the plant and stunts flower growth, turning the petals green. There is no cure for the disease and the plants must be pulled and destroyed. Control the insect and the disease will not affect the plant.

Pests

• Several pests can cause coneflowers to weaken and die. Aphids feed on the juices of the plant and weaken it so that it invites bacterial and fungal infections to strike. Aphids have small pear-shaped green or brown bodies. They reproduce very fast and can soon cover the stems and flowers. The flower discolors, wilts and dies if infestations are large. Treat plants with insecticidal soap or horticultural oils. Fleahoppers are small yellow to green insects, and they have both wings and large legs with which to jump. They, like aphids, feed on the juices of the plants. They cause dark spots and distorted leaves. Keeping a clean garden usually discourages an infestation. Eriophyid mites affect flowers by distorting them and causing them to wither and fall. Plants must be destroyed.