According to the British Columbia Department of Agriculture, Food and Fisheries, purple coneflower, also known as Echinacea purpurea, is prized for its medicinal properties and is believed to be helpful in fighting against colds, sore throats, toothaches, burns, poison ivy and snakebites. This wildflower grows well in the moist conditions along the banks of rivers and creeks or in a well-tended backyard garden. Although a fairly hardy plant, purple coneflowers are susceptible to a few pests and diseases.
Brown ambrosia, melon and green peach aphids attack purple coneflowers. These tiny pear-shaped insects feed on sap and fluid from the plant’s stems and leaves and then secrete a sugary substance that attracts sooty mold fungus. Aphids multiply quickly and can do extensive damage. Ladybugs are natural aphid predators, but insecticidal soaps are also effective against aphids.
Garden fleahoppers also suck sap from the stems and foliage of the purple coneflower causing bleached or dark-colored coarse spots measuring up to 1/16 inch in diameter. Leaves become distorted, flowers drop, and the plant may die if heavily infested. Garden fleahoppers can produce up to five generations in a single season. However, a single application of pesticide should be adequate for control.
The greenish-yellow aster leafhopper is long, slender and wedge-shaped, measuring about 1/8 inch long and sporting six black spots on its head. Aster leafhoppers spread the viral-like disease aster yellows to purple coneflowers as they suck the sap from the plant during feeding. Leaves will yellow and flowers will be deformed on plants with aster yellows. The disease is not fatal, but the infected plant will never grow and produce as intended. Verbena, salvia and geranium are companion plants to grow with purple coneflowers to prevent aster leafhoppers from infecting the plants.
Sweet potato or silverleaf whiteflies may also infest purple coneflowers. These tiny white flies can be found on the underside of the leaves and will fly up when the leaves are disturbed. Whiteflies suck sap and nutrients from the plant, weakening the plant and stunting its growth. Like aphids, whiteflies excrete a sweet sticky substance that attracts sooty mold fungus. Neem oil, insecticidal soaps, horticultural oils and whitefly traps are effective means of controlling whiteflies.
In northern gardens, Japanese beetles will eat the foliage of purple coneflowers and disfigure the plants. These metallic green and coppery brown oval insects have a voracious appetite for foliage. Synthetic or chemical pesticides labeled for use against Japanese beetles provide control of these hungry pests.