From my perspective as an oleander (*Nerium oleander*), my leaves are my life. They are my solar panels, my respiratory system, and my primary defense against the environment. When brown spots appear, it is a clear sign of distress—a symptom of an internal imbalance or an external attack. These spots disrupt my ability to photosynthesize, weakening me and making me vulnerable. Understanding the cause is not just about aesthetics; it is about my survival and ability to thrive.
The appearance, location, and pattern of the brown spots are critical diagnostic clues. I cannot speak, so my leaves must communicate for me.
This is a severe, systemic bacterial infection that fills my xylem vessels, the tubes I use to transport water from my roots. The blockage prevents water from reaching my leaves. The symptoms begin with a marginal scorch: the edges and tips of my leaves turn yellow, then brown and crispy, while the leaf vein often remains green. This browning progresses inward, eventually causing the leaf to die and fall. If you see this pattern, especially if it starts on one branch and spreads, it is a grave concern. There is no cure, and I will eventually succumb.
Fungal pathogens are common invaders, especially in warm, humid, or wet conditions. They attack my leaf tissue directly. The spots they cause are typically circular or angular and can be brown, black, or even have a yellow halo. You might see tiny black dots within the spots—these are the fungal fruiting bodies. Unlike the marginal pattern of leaf scorch, fungal spots are scattered randomly across the leaf surface. They thrive when my foliage remains damp for extended periods, often due to overhead watering or poor air circulation.
Bacterial spots are often water-soaked initially, appearing as dark, greasy-looking patches on my leaves. As they develop, they turn brown or black and may be surrounded by a yellow ring. These spots can cause the leaf to become distorted or ragged if the dead tissue falls out. Bacteria enter through natural openings or wounds, spreading rapidly in splashing water from rain or irrigation.
Sometimes, the cause is not biological but environmental. If my roots are waterlogged, they cannot breathe, leading to root rot. This prevents water uptake, causing drought-like symptoms, including brown spots and leaf drop. Conversely, chemical burn from fertilizer salts or pesticides can also manifest as brown, scorched spots, particularly if applied in high concentration or during the heat of the day. Physical damage can also create localized brown areas.
The treatment depends entirely on an accurate diagnosis of the cause.
Immediately isolate me to prevent potential spread to other plants via insect vectors like leafhoppers. There is no cure. The only action is to remove and destroy severely infected branches to slow the progression, but ultimately, I will need to be removed entirely to protect other oleanders.
First, improve my growing conditions. Water me at the base, not from overhead, to keep my leaves dry. Ensure I have plenty of space for air to circulate around my foliage. Prune away the most severely affected leaves and branches, disinfecting your pruning tools between cuts to avoid spreading pathogens. For persistent fungal problems, a fungicide containing chlorothalonil or copper may be applied according to label instructions. For bacterial spots, copper-based sprays can offer some suppression, but cultural controls are most effective.
Correct the underlying issue. Ensure I am planted in well-draining soil and adjust your watering schedule so my roots are moist but never saturated. If chemical burn is suspected, leach the soil with deep, slow watering to flush out excess salts. Protect me from physical damage from lawn equipment or harsh weather where possible.
