Greetings from the garden. We, the azaleas, are renowned for our vibrant spring displays, but our beauty is often challenged by various afflictions. To help you help us, here is a detailed account of the most common pests and diseases we face in American gardens, told from our perspective.
Several tiny creatures threaten our vitality by piercing our tissues and consuming our sap. The Azalea Lace Bug (Stephanitis pyrioides) is our most notorious foe. Adults and nymphs feed on the undersides of our leaves, removing chlorophyll. This results in a tell-tale stippling of white or yellow spots on the upper leaf surface, with dark, varnish-like excrement spots below. A severe infestation leaves us weak, grayish, and unsightly. Spider Mites are another microscopic menace, especially in hot, dusty conditions. They cause a similar stippling or bronzing of our leaves, often accompanied by fine webbing. Aphids and Whiteflies also cluster on our tender new growth, sucking sap and excreting sticky honeydew that fosters the growth of sooty mold, which further inhibits our photosynthesis.
Our foliage and branches are primary targets. Azalea Leafminers (Caloptilia azaleella) are the larvae of small moths that tunnel inside our leaves, creating blotchy mines. They eventually cause leaf curling, browning, and premature drop. Leaf Gall, caused by the fungus Exobasidium vaccinii, is a startling but often less serious springtime disease. It causes our leaves or flowers to become pale green, thickened, and fleshy, eventually turning white and powdery as the fungus spores.
The most severe threats often attack us from below the soil line. Phytophthora Root Rot (caused by Phytophthora spp.) is a deadly water mold that thrives in poorly drained, soggy soils. It attacks our roots, preventing water and nutrient uptake. Above ground, our leaves wilt, turn yellow or reddish, and curl inward, despite adequate soil moisture. The branches become brittle and die. This is often fatal. Similarly, Armillaria Root Rot (Oak Root Fungus) attacks our root system, leading to a sudden collapse and death. White fungal mats between the bark and wood are a key identifier.
Other fungi target our above-ground parts directly. Powdery Mildew (Erysiphe spp.) coats our leaves with a distinctive white, powdery fungal growth, typically in late summer to fall. It is more unsightly than deadly but can stress us and reduce our vigor. Petal Blight (Ovulinia azaleae) is a rapid and devastating disease for our flowers. It causes small, water-soaked spots that quickly enlarge into soft, brown blotches, causing the entire flower to collapse into a slimy mess within days, especially in warm, moist, spring conditions.
