The purple coneflower was formerly known as the Rudbeckia purpurea and is a member of the Compositae family. Producing large colorful blooms, the purple coneflower stands between 2 and 4 feet in height. While this plant is relatively free of pests, it is susceptible to infestation by the Japanese beetle which can affect the health and vigor of the plant.
Japanese beetles are potentially damaging pests that commonly attack the purple coneflower. Native to Japan, this pest was first found in 1919 in the state of New Jersey. Japanese beetles develop in the soil as white grubs. Adult Japanese beetles emerge from the soil and are approximately 7/16 inches in length, with a metallic green body with brown wings. Both the grub and the adult beetle feeds on the purple coneflower causing extensive damage. Large populations of Japanese beetles can cause severe injury to host plants.
Japanese beetles feed on over 300 species of plants. The purple coneflower feeds on leaves, chewing out the tissues in the upper leaf surfaces. This results in skeletonized leaves and leaf scorching. Beetles may completely consume flower petals, with most beetles starting at the top of the flower and working their way down the plant. Heavy infestations of Japanese beetles may kill host plants.
Hand-picking beetles from your purple coneflowers is one way to control light infestations of Japanese beetles. Remove beetles from small plants by shaking them from the plant. This works best in the early morning hours, as Japanese beetles are sluggish in the morning. Shake them into a bucket of soapy water. Covering your purple coneflowers with netting may also help discourage Japanese beetle feeding.
There are a wide variety of insecticides labeled for Japanese beetle control available at your local garden center. With any chemical control product, it is important to thoroughly cover the foliage and flowers with insecticides for optimal results. Reapply insecticides to your coneflowers periodically to avoid re-infestation. Follow all instructions indicated on the label of the insecticide for best results.