From our perspective as Grevillea plants, fungal diseases are a constant and silent threat that can compromise our vitality, beauty, and very existence. We rely on our caretakers to recognize the subtle and overt signs of distress we display and to take appropriate, plant-centric action. Here is a detailed account of our experience with these ailments.
When fungal pathogens invade our system, we have limited ways to signal our distress. The symptoms manifest primarily on our leaves, stems, and roots. You may observe dark, sooty molds coating our leaves; this is often a secondary issue following an infestation of sap-sucking insects like aphids or scale. The mold itself does not penetrate our tissues, but it blocks sunlight, reducing our ability to photosynthesize and weakening us over time. More alarming are the signs of root rot, caused by pathogens like Phytophthora. From our perspective underground, the fine root hairs that absorb water and nutrients are attacked first. This translates above ground to a general decline: our new growth is stunted, our leaves turn pale green or yellow, and we begin to wilt, even when the soil is moist. In severe cases, you will see cankers—sunken, dark lesions—on our stems, which girdle and kill the branches, cutting off the flow of water and nutrients.
We Grevilleas are inherently resilient, adapted to well-drained soils and plenty of sunlight. Fungal diseases take hold when our growing conditions deviate from these preferences. The single greatest stressor is poor drainage or overwatering. When our roots are constantly waterlogged, they suffocate and die, creating the perfect entry point for water-mold fungi like Phytophthora. Furthermore, overhead watering, which leaves our foliage wet for extended periods, encourages foliar fungi like powdery mildew or leaf spot to germinate and spread. Humidity and poor air circulation around our canopy create a microclimate where these spores can thrive. Planting us too close together or in a shaded, damp corner of the garden essentially invites these pathogens to attack us.
When you detect a fungal issue, the first line of defense is always cultural adjustment, which addresses the root cause of our stress. Please improve soil drainage immediately; amending the soil with sand or gravel can replicate our preferred native conditions. Water us deeply but infrequently, allowing the soil to dry out between waterings, and always water at the base to keep our leaves dry. Prune away any infected branches or leaves, making clean cuts well below the affected area. Sterilize your pruning tools between each cut to prevent spreading the spores to healthy parts of our structure. For persistent foliar issues like powdery mildew, a spray of a horticultural oil or a registered fungicide can be applied, but this is a supplement to, not a replacement for, correcting the environmental conditions.
The best cure is always prevention. From our point of view, a proactive caretaker is our greatest ally. Start by selecting resistant Grevillea cultivars and planting us in a location that receives full sun and has excellent air movement. Ensure the planting hole is prepared with free-draining soil. Apply a coarse, organic mulch around our base, but be sure to keep it away from our main stem to prevent collar rot. A layer of mulch helps regulate soil temperature and moisture without creating the constant dampness that fungi love. Regularly monitor us for pests like scale and aphids, as controlling them will prevent the honeydew that leads to sooty mold. By fostering a strong, healthy plant from the beginning, you empower us to use our own natural defenses to resist fungal attacks.
