From our perspective as Coreopsis plants, we are generally resilient and low-maintenance, but we are not invincible. Our vibrant blooms and lush foliage can be compromised by a variety of pests and diseases that find us as appealing as gardeners do. Understanding these threats from our point of view is key to ensuring we remain healthy and flourish in your gardens.
Several insects see our sap and foliage as a primary food source. Aphids are a frequent nuisance; these tiny, soft-bodied insects cluster on our tender new growth and undersides of leaves, sucking out our vital fluids. This weakens us, causing leaf distortion and a sticky residue known as honeydew, which can attract other problems. Another significant pest is the leafhopper. These small, wedge-shaped insects also feed on our sap, but their damage is twofold: they directly stress us and can act as vectors, transmitting harmful plant pathogens as they move from plant to plant.
Furthermore, during our blooming period, thrips can become a problem. These minute, slender insects feed within our flower buds, causing them to become distorted, streaked with discoloration, or fail to open entirely. This directly impacts our reproductive goal of producing beautiful, viable flowers. Lastly, while less common, infestations of foliar nematodes can be devastating. These microscopic roundworms live in the soil and swim up our stems in water, entering our leaves through pores. They feed on our internal cells, causing unsightly angular, yellow-to-brown lesions between the veins that can eventually lead to leaf drop and severe decline.
Fungal diseases are our most common adversaries, often encouraged by environmental conditions that are out of our control. Powdery mildew is a widespread issue, presenting as a white, powdery coating on our leaves and stems. It thrives in humid conditions with poor air circulation, blocking sunlight and interfering with our photosynthesis. Similarly, downy mildew can appear, causing light green or yellow angular spots on the upper leaf surfaces and a downy grayish-white growth on the undersides.
More serious are the root and crown rots, such as those caused by Sclerotinia or Rhizoctonia fungi. These pathogens thrive in waterlogged, poorly draining soil, a condition that is very stressful for our root systems. They attack our crown and roots, causing a rapid wilt and collapse of the entire plant, often turning our lower stems brown and mushy. Another foliar disease we contend with is Alternaria leaf spot, which causes small, dark brown to black spots with concentric rings on our leaves. These spots can coalesce, leading to significant leaf yellowing (chlorosis) and premature defoliation, which severely reduces our vigor.
Beyond fungal issues, we are susceptible to systemic viral infections like Aster Yellows. This phytoplasma disease is spread primarily by leafhoppers. Once infected, our entire system is compromised. We exhibit bizarre symptoms including yellowing (chlorosis), stunted growth, and strangely deformed flowers that may remain green and fail to develop proper petals (phyllody). This disease is particularly disheartening as it is incurable; it disrupts our very growth processes from the inside out.
