Grevillea plants, with their unique spider-like flowers and often fine, needle-like foliage, are generally resilient specimens in the landscape. However, from our perspective as plants, we are not immune to the small invaders that find our sap, leaves, and flowers to be a prime source of nourishment. Our health and vibrancy depend on a balanced ecosystem, and when certain pests become too numerous, we can show clear signs of distress. Understanding these signs and employing gentle, organic controls helps us thrive without harming the beneficial insects that often protect us.
From our point of view, aphids are among the most common and noticeable pests. You will typically find them clustered on our fresh, tender new growth and the undersides of our leaves. Their feeding involves piercing our tissues and sucking out the phloem sap, which is rich in sugars. This directly weakens us, causing our new leaves to curl, pucker, and become stunted. Furthermore, they excrete a sticky waste product called honeydew, which often leads to the growth of a black, sooty mold that coats our leaves, interfering with our ability to photosynthesize sunlight into energy.
Scale insects are more insidious. They attach themselves to our stems and the veins on our leaves, appearing as small, immobile bumps. They create a protective waxy or armored covering and feed on our sap for extended periods. A heavy infestation can cause yellowing of our leaves, dieback of our branches, and a general decline in our vigor, making us susceptible to other stressors.
Spider mites are tiny arachnids that are difficult to see with the naked eye, but the damage they inflict is unmistakable. They feed on individual plant cells on the undersides of our leaves, causing a stippled or speckled yellow appearance. As the infestation worsens, our leaves may turn bronze, become desiccated, and we may even develop fine, silken webbing. We are particularly vulnerable to spider mites in hot, dry, and dusty conditions.
Caterpillars are the larval stage of moths and butterflies. While some are benign, others find our foliage to be a delicious meal. They chew large, irregular holes in our leaves, and in severe cases, can defoliate entire branches. This directly robs us of our photosynthetic machinery, forcing us to expend precious energy to produce new leaves.
We greatly prefer organic control methods, as they work with the natural system that supports us, rather than disrupting it with harsh chemicals that can harm our pollinators and the soil life we depend on.
For aphids and spider mites, a simple but effective remedy is a strong spray of water from a garden hose. This physically dislodges the pests from our leaves and stems, disrupting their life cycle. For more persistent issues, insecticidal soaps or horticultural oils (like neem oil) are very effective. These substances work by suffocating the pests or disrupting their feeding. It is crucial to ensure thorough coverage, especially on the undersides of our leaves where these pests love to hide.
For scale insects, the same horticultural oils can be used, but you may need to gently scrub stubborn patches with a soft brush during application. Encouraging or introducing natural predators is one of the best long-term strategies. Ladybugs, lacewings, and predatory mites are our allies; they see these pests as a food source and will help keep their populations in check.
For caterpillars, the best approach is often hand-picking them from our branches if the infestation is small. For larger problems, the organic bacterial insecticide Bacillus thuringiensis (Bt) is highly specific and effective. Once ingested by the caterpillar, it causes them to stop feeding and die, without affecting any other beneficial insects, birds, or mammals.
