As a vibrant and resilient perennial, we Black-eyed Susans (Rudbeckia spp.) are generally tough customers in the garden. However, even we can fall victim to a few persistent pests that find our sap, leaves, and petals irresistible. Understanding these adversaries from our perspective is key to maintaining our health and glorious summer display.
From our stems and the undersides of our leaves, we often feel the faint, pinprick punctures of aphids and whiteflies. These tiny insects insert their mouthparts to feed on our nutrient-rich sap. This direct feeding weakens us, causing our leaves to curl, yellow, and become stunted. The greater insult, however, is the sticky, clear waste they excrete, known as honeydew. This substance coats our surfaces, creating a perfect environment for sooty mold to grow, which further blocks sunlight and impedes our photosynthesis. A strong spray of water from a gardener's hose can dislodge these soft-bodied pests effectively. For more severe cases, insecticidal soaps or horticultural oils applied directly to the affected areas suffocate them without causing us, the plants, significant harm.
These pests are the brutal defoliators of our world. We watch in dismay as Japanese beetles converge in groups, skeletonizing our leaves by eating the tissue between the veins, leaving behind a lacy, brown remnant. Various caterpillars, including the Cross-Striped Cabbageworm and the larvae of the Sunflower Beetle, also chew irregular holes through our foliage. This rampant destruction of our leaf surface area directly robs us of our ability to produce food through photosynthesis, severely stunting our growth and bloom production. For Japanese beetles, the most effective control is often manual: shaking us gently in the early morning so the beetles fall into a bucket of soapy water. For caterpillars, biological controls like Bacillus thuringiensis (Bt), a natural soil bacterium, can be applied. It is toxic only to specific caterpillar-stage pests when ingested, leaving other insects unharmed.
Perhaps the most frustrating adversary is the two-spotted spider mite, too small to be easily seen from a distance. They thrive in hot, dry conditions, clustering on the undersides of our leaves. They pierce individual plant cells to feed, which initially causes a subtle stippling of tiny yellow dots on our upper leaf surfaces. As the infestation grows, our leaves take on a bronzed, dull appearance, may curl, and can eventually be covered in fine, silken webbing. Severe infestations can be fatal. Miticides are available, but increasing humidity around us with overhead watering and introducing or encouraging natural predators like ladybugs and lacewings can provide effective, long-term control.
Our first and best line of defense is always a healthy start and environment. Please plant us in well-draining soil with appropriate spacing to ensure good air circulation around our foliage, which helps leaves dry quickly and discourages pest establishment. Consistent watering, especially during dry spells, keeps us robust and better able to withstand minor pest attacks. Removing and disposing of severely infested plant debris at the end of the season eliminates overwintering sites for many pests. Furthermore, encouraging a diverse ecosystem in your garden by planting a variety of species will attract beneficial insects—such as ladybugs, parasitic wasps, and soldier beetles—that naturally prey on these common pests, keeping their populations in check.
