Root Rot

• Seedlings collapsing at the soil line with a water-soaked, pinched stem — damping-off, the most common seedling form
• Established plants wilting during the day and failing to recover overnight, despite moist soil — roots are not functioning
• Roots that appear brown, black, or slimy rather than firm and white when the plant is pulled
• Lower leaves yellowing and dropping while the rest of the plant looks stressed — the root system is progressively failing
• Fruit and foliage symptoms out of proportion to any visible above-ground issue — the problem is underground
• Standing water or persistently wet soil in the area where affected plants are growing

Root rot is caused by several unrelated pathogens that share an affinity for waterlogged, oxygen-depleted soil. Pythium and Phytophthora are water molds (oomycetes), not true fungi — they produce swimming spores that move through free water in soil pores, which is why wet conditions trigger explosive spread. Rhizoctonia is a true fungus that causes both damping-off and root rot in older plants. These organisms are present in most garden soils at low levels; the disease develops when soil oxygen drops due to overwatering, poor drainage, or compaction. Once roots are destroyed, secondary bacteria often colonize the tissue, accelerating collapse.

1. 01Improve drainage before planting: work compost into heavy soil, plant in raised beds, or create mounded rows — this is the most durable fix
2. 02Avoid overwatering; let the top inch or two of soil dry between waterings for most vegetables
3. 03Do not plant into cold, wet soil in early spring — Pythium is most active in cool, saturated conditions that often follow spring rain
4. 04For seedlings: use a sterile, well-drained seed-starting mix and avoid reusing potting soil between batches
5. 05Drench transplant holes with a beneficial Trichoderma product (a competing fungus sold as RootShield or similar) when planting into soil with a root rot history
6. 06Remove and dispose of infected plants promptly — do not compost roots showing rot; the pathogens persist in plant tissue

If plants are dying repeatedly in the same area of the garden despite improved drainage, an extension diagnostic lab can identify which pathogen is responsible — Pythium, Phytophthora, and Rhizoctonia each respond somewhat differently and identifying the genus helps target management.

• Root Rots of Vegetables— University of Minnesota Extension
• Damping-Off and Root Rot— UC ANR Integrated Pest Management