Common Houseplant Diseases — Diagnosis & Treatment
Last Updated: February 2026
TL;DR
The five most common houseplant diseases are root rot (from overwatering), powdery mildew (from poor air circulation), leaf spot (bacterial or fungal), spider mites, and fungus gnats. Most are preventable through proper watering, ventilation, and regular inspection. Early detection is critical — check the undersides of leaves weekly.
| Disease/Pest | Key Symptom | Cause | Severity |
|---|---|---|---|
| Root Rot | Mushy brown roots, yellow leaves | Overwatering | ⚠️ High |
| Powdery Mildew | White powder on leaves | Stagnant air, humidity | Medium |
| Leaf Spot | Brown spots with yellow halos | Fungi or bacteria | Medium |
| Spider Mites | Fine webbing, speckled leaves | Dry conditions | ⚠️ High |
| Fungus Gnats | Tiny flies near soil | Wet topsoil | Low |
| Scale Insects | Brown bumps on stems | Introduced from new plants | Medium |
Root Rot: The #1 Plant Killer
Root rot is a fungal condition caused by roots sitting in waterlogged soil for extended periods. The fungi Pythium and Phytophthora thrive in anaerobic (low-oxygen) conditions created by saturated soil, attacking healthy roots and turning them brown and mushy.
Symptoms progress in stages: first, subtle slowed growth and slightly wilting leaves. Then yellowing of lower leaves. Finally, the entire plant wilts — even when the soil is wet. By this stage, significant root damage has already occurred.
Treatment: Unpot the plant, wash all soil from roots, cut away every brown or mushy root with sterile scissors, and repot in fresh, well-draining soil. Water sparingly until new growth appears. For detailed overwatered plant rescue steps, see our dedicated guide.
Pests: Prevention and Treatment
Fungus gnats are the most common pest annoyance, though they rarely cause serious damage. Spider mites and scale are more dangerous — they sap nutrients from plants and can kill weakened specimens if untreated.
The best prevention is quarantining new plants for 2-3 weeks before placing them near your collection, inspecting leaf undersides weekly, and maintaining consistent environmental conditions. Stressed plants are more susceptible to infestation.
Using AI for Plant Diagnosis
Modern AI tools can diagnose plant diseases from a single photo with 80-90% accuracy. By scanning a photo of affected leaves, AI identifies disease patterns, suggests likely diagnoses, and provides specific treatment steps. This is particularly useful for distinguishing between similar-looking conditions (e.g., overwatering vs. underwatering, which share some symptoms). Learn more about how AI plant identification works.
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Frequently Asked Questions
Root rot is the most common houseplant disease, caused primarily by overwatering. It affects the roots first, causing them to turn brown and mushy, then progresses to yellowing leaves and wilting. Prevention through proper watering is more effective than treatment.
Mild to moderate root rot is treatable if caught early. Remove the plant from its pot, trim all brown/mushy roots with sterile scissors, repot in fresh dry soil, and reduce watering. Severe root rot (more than 75% of roots affected) is usually fatal.
Common signs of fungal infection include white powdery patches (powdery mildew), brown or black spots with yellow halos (leaf spot), fuzzy gray mold (botrytis), and soft mushy stems (stem rot). Fungal issues thrive in humid, poorly ventilated conditions.
Yes, most fungal and bacterial plant diseases can spread to nearby plants through water splashing, physical contact, contaminated tools, or airborne spores. Isolate sick plants immediately and sterilize any tools used on infected plants.
Yes, promptly removing diseased leaves helps prevent the spread of infection. Use clean, sharp scissors and cut the entire leaf including the petiole (stem). Discard removed leaves in the trash, not compost, to prevent reinfection.
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