Impatiens Stem Rot: Rhizoctonia Crown Rot

The black, withered stems at soil level causing sudden wilt and break-off on your impatiens is Rhizoctonia crown rot (Rhizoctonia solani), a soil-borne fungus favored by wet, heavy soils and deep planting.

Symptoms

• Brown/black lesions at soil line.
• Sudden collapse, no prior leaf symptoms.
• Spreads plant-to-plant via soil water splash.

Control

1. Remove and destroy infected plants immediately (roots + soil).
2. Improve drainage: Raised beds, coarse organic matter, avoid low spots.
3. Water at base only—no overhead. Morning watering.
4. Space plants for air flow.
5. Fungicide (preventive): Thiophanate-methyl (Cleary's 3336) or iprodione at planting and 2–3 weeks later.
6. Rotate crops—don't plant impatiens in same bed yearly.

Key Insight

Once stems are black at soil line, fungicide sprays won't cure—the fungus is inside the crown. Prevention at planting is everything. Consider New Guinea impatiens (more resistant) or begonias for that bed next year.