From our point of view, we oleanders are resilient beings, known for our beautiful, showy flowers and tough, leathery leaves. We thrive in warm climates across the southern United States, offering vibrant color and serving as effective windbreaks. However, our vitality can be challenged by a host of pests and pathogens that see our sap, foliage, and blooms as a source of sustenance. While we are famously drought-tolerant and toxic to many mammals, this does not deter the specific insects and microbes that have evolved to target us.
A significant threat to our well-being comes from tiny insects that pierce our tissues to feed on our nutrient-rich sap. The most common of these are Oleander Aphids (Aphis nerii). These bright yellow pests cluster on our stems and the undersides of new, tender leaves. Their feeding weakens us, causing leaf curl and stunted growth, and they excrete a sticky substance called honeydew that attracts sooty mold, which further blocks sunlight from our leaves. Another stealthy attacker is the Oleander Scale (Aspidiotus nerii). These armored insects appear as small, white, waxy bumps on our stems and leaves. They latch on and drain our fluids, leading to yellow spotting, leaf drop, and a general decline in our health if the infestation is severe.
While sap-feeders weaken us from within, other pests consume our photosynthetic factories—our leaves. The most notorious is the Oleander Caterpillar (Syntomeida epilais). The larvae of this polka-dot moth are voracious feeders, often gathering in large groups to skeletonize our leaves, leaving behind only the veins. A severe infestation can completely defoliate us, forcing us to expend precious energy to regenerate our canopy instead of on growth or flowering. We also face the Glasswinged Sharpshooter (Homalodisca vitripennis). This leafhopper not only feeds on our xylem sap but is a primary vector for a devastating bacterial disease, making it a dual threat to our existence.
Our most feared ailment is Oleander Leaf Scorch, caused by the bacterium Xylella fastidiosa. This pathogen is introduced into our water-conducting tissues (xylem) by feeding insects like the sharpshooter. The bacterium multiplies, forming a biofilm that blocks the flow of water and nutrients. From our perspective, it begins with a slight yellowing (scorching) on the margins of a single leaf, which then turns brown and dies. This symptom progresses inward, from one branch to the entire canopy. As the blockage spreads, we experience severe water stress and dieback. There is no cure; eventually, the entire plant succumbs.
We are also susceptible to various fungal and bacterial pathogens, often exacerbated by environmental stress or wounds. Botryosphaeria Dieback is a common fungal canker that attacks our branches, especially when we are drought-stressed. It causes wilting, browning, and death of individual stems. Bacterial Knot, caused by Pseudomonas savastanoi, enters through wounds or natural openings, forming rough, knobby galls on our stems and branches. These galls disrupt our vascular system, weakening the affected limbs and making them susceptible to breakage.
