Common Houseplant Pests and Diseases

Even the most attentive plant parent encounters pests and disease at some point. Early detection and swift, appropriate action prevents minor infestations from becoming plant-threatening crises. Knowing what to look for — and how to respond — keeps your collection healthy.

Spider mites are among the most common and damaging houseplant pests, particularly in warm, dry indoor environments. They are tiny (barely visible without magnification) and typically appear as very fine webbing on leaf undersides, with stippled, faded, or bronzed upper leaf surfaces. Tap a suspect leaf over white paper — dislodged mites appear as tiny moving dots. Treat by wiping leaves with damp cloth, applying insecticidal soap spray, or using neem oil. Increase humidity, as mites thrive in dry conditions.

Fungus gnats are small, dark flies buzzing around the soil surface and base of plants. Adults are merely annoying, but their larvae feed on fine root hairs and tender roots, stunting growth and opening pathways for disease. They breed exclusively in moist soil. Allow the top layer of soil to dry out more between waterings — this breaks the breeding cycle. Sticky yellow traps catch adults. Bacillus thuringiensis israelensis (Bti), sold as mosquito dunks, applied as a soil drench kills larvae effectively.

Mealybugs appear as white, cottony masses at leaf axils, stem junctions, and leaf undersides. They secrete honeydew that promotes sooty mold growth. Isolate affected plants immediately. Remove visible mealybugs with a cotton swab dipped in 70% isopropyl alcohol. Follow up with neem oil sprays every 5-7 days for several weeks to catch new hatchlings from eggs.

Scale insects appear as small, brown, tan, or waxy bumps firmly adhered to stems and leaf surfaces. Soft scales secrete honeydew; armored scales do not. Scrape off visible scale with a soft toothbrush, then treat with horticultural oil or 70% isopropyl alcohol applied directly. Systemic insecticides (imidacloprid granules) work for severe infestations when other methods fail.

Aphids cluster on new growth, tender shoot tips, and flower buds, sucking plant sap and excreting honeydew. They reproduce rapidly. A strong water spray removes them from sturdy plants. Insecticidal soap or neem oil applied every few days controls established colonies. Lacewings and ladybugs, if you can source them, provide biological control.

Root rot is the most common and devastating disease of houseplants, caused primarily by overwatering leading to anaerobic soil conditions where Phytophthora, Pythium, and Fusarium fungi thrive. Symptoms include wilting despite moist soil, mushy brown or black roots (healthy roots are white or tan and firm), and a sour smell. Treatment requires removing the plant from its pot, cutting away all affected roots with sterile scissors, dusting roots with cinnamon or powdered sulfur (natural fungicides), and repotting in fresh well-draining mix. Reduce watering going forward.

Powdery mildew appears as a white, powdery coating on leaf surfaces, usually in conditions of poor air circulation combined with high humidity. It rarely kills plants but weakens them and spreads to neighbors. Remove heavily affected leaves, improve air circulation, reduce leaf wetness, and apply a baking soda spray (1 tsp baking soda per liter water) or diluted neem oil to affected areas.

Prevention remains far more effective than treatment. Quarantine all new plants for 2-3 weeks before placing them near existing plants. Inspect the undersides of leaves and soil surface of every new purchase before bringing it home. Maintain plant hygiene by wiping leaves periodically and removing dead leaves and spent flowers. Stressed plants attract pests — healthy growing conditions provide the best long-term defense.