If your orchid’s glossy, green leaves or usually immaculate flowers have suddenly sprouted unsightly brown bumps, it’s time for action. You’re looking at one of two possible culprits, and treating the plant for the wrong one will only add to its woes. Fortunately, distinguishing between the two is easy.
Whether it's an outdoor showy lady's slipper orchid (Cypripedium reginae) in U.S. Department of Agriculture plant hardiness zones 2 through 7 or a heat-loving moth orchid (Phalaenopsis spp.) in zones 10 through 12, an orchid with oedema is overwatered: Its roots are drinking more water than its above-ground tissues can release. The flooded cells form permanent blisters, often with corky brown topping. Prevent oedema by watering in the morning, letting the pot drain and waiting until the growing medium’s surface dries before watering again.
Brown Soft Scale Insects
If the brown bumps come away from the orchid when you rub them, they're brown soft scales. These dome-shaped insects with straw-like mouths attach to leaves and petals, draining sap and excreting sticky waste. Remove adult scales with a soft toothbrush, then kill the larvae with cotton swabs dipped in isopropyl alcohol. To protect the leaves, remove the alcohol residue with a tissue.
- George Doyle/Stockbyte/Getty Images