Satsuma tangerine trees (Citrus reticulata) can be as close to perfect as citrus trees get. The most cold-tolerant of all citrus, they develop in U.S. Department of Agriculture plant hardiness zones 8b through 11. They’re also small enough to grow as houseplants while producing delightfully fragrant spring blooms and sweet, juicy winter. If you are accustomed to satsuma’s virtues, having oily black smears blemish it may be unsettling. The black is sooty mold, the aftermath of a pest infestation. Use oil sprays to eliminate the insects responsible, and sooty mold eventually disappears on its own.
Aphids and Whiteflies
Tiny aphids and whiteflies sometimes target satsumas, pierce their leaf tissue with syringelike mouths and drain the nitrogen-rich sap. They cluster on the undersides of their leaves. Pear-shaped aphids may be green, yellow or black. Winged, white or pale-yellow whiteflies swarm briefly from the trees when disturbed. Aphids attack throughout the trees’ four yearly growth flushes and decline when the new leaves mature. Whiteflies are busy in early spring, midsummer and early to midfall.
Honeydew and Sooty Mold
Sooty mold develops on satsumas when the aphids or whiteflies excrete honeydew, a transparent, sticky waste. Airborne sooty mold spores feed on the honeydew but don’t penetrate the leaves. The spores form colonies of black fungus, sometimes thick enough to block sunlight and interfere with photosynthesis. Even small amounts of sooty mold ruin a satsuma’s look. Removing the insects with oil spray additionally eradicates honeydew, and the sooty mold eventually starves.
Plant-Based Neem Oil
Organic, ready-to-use neem oil suffocates aphids and whiteflies. Because neem oil overspray can stain surrounding surfaces, cover the area around an indoor satsuma, or move the tree outside for therapy after watering it well. If you are spraying outside, take action on a peaceful day to reduce drift from hitting other plants. Shake the spray bottle frequently to maintain the oil frozen, and coat each side of the leaves till they drip.
Organic Horticultural Oil
A refined petroleum product, olive oil works like neem oil. Use it at the first sign of aphids or whiteflies. On a calm, dry day, when the temperature is below 90 degrees Fahrenheit and no rainfall is in the forecast, water your satsuma well and spray until all of its surfaces drip. Go an indoor tree outside for therapy. Keep people and pets away from the sprayed area while the oil dissolves, and repeat the program whenever more aphids or whiteflies arrive.
Take Precautions
Keep the oils out of your neighborhood water distribution by spraying your satsuma just when the weather is dry and there’s no chance that their runoff might reach drains or nearby water resources. The oils suffocate bees and other beneficial insects on contact, so examine your tree for good insects and delay spraying it they are present. To guard against potential eye, respiratory or skin irritation, dress at a long-sleeved shirt, long pants, waterproof gloves, socks, shoes, protective masks and a respiratory mask when spraying. Keep people and pets away from the sprayed area until the oil dries.