As a resilient and sun-loving plant, African Daisies (Osteospermum spp.) generally thrive in the warm, well-drained conditions of many US gardens. However, our physiology and growth habits make us susceptible to specific environmental stresses and pathogens. The following details the primary adversaries we face from a plant's perspective.
From our viewpoint, the most common assault comes from tiny, sap-sucking insects. Aphids congregate on our succulent new growth and the undersides of our leaves, piercing our tissues to drain our vital fluids. This not only weakens us, causing our leaves to curl and distort, but their sticky excrement, known as honeydew, fosters the growth of sooty mold, which blocks sunlight from our leaves. Similarly, spider mites, which thrive in hot, dry weather, weave fine silken webs on our foliage as they feed, leaving us with a stippled, yellow, and overall dehydrated appearance, severely compromising our photosynthetic capabilities.
Our broad, green leaves are prime targets for fungal diseases, especially when our foliage remains damp for extended periods. Powdery mildew appears as a white, powdery coating on our surfaces, hindering our ability to breathe and photosynthesize efficiently. It is often a sign that our planting is too dense or that overhead watering is keeping our leaves wet. More dangerously, pathogens like Pythium and Phytophthora lie in wait in waterlogged, poorly draining soil. When our roots are suffocated and constantly wet, these fungi attack, causing a fatal root rot. From our perspective, this is a silent killer; the first sign you see above ground—wilting and collapse—occurs only after our root system has been destroyed beyond recovery.
It is crucial to understand that many of our problems are secondary to environmental conditions that are not ideal for our native South African origins. We are fundamentally drought-tolerant plants that demand excellent drainage and full sun. When planted in heavy, clay-rich soil or shaded areas, we become stressed. This stress weakens our natural defenses, making us far more inviting to the pests and diseases mentioned above. Furthermore, excessive nitrogen fertilization promotes an overabundance of soft, succulent growth, which is particularly attractive to aphids and more susceptible to powdery mildew infection.
