Diagnosing St. John's Wort Decline: Rust, Nematodes, or Drainage Issues

Creeping St. John's wort (Hypericum calycinum) turning brown with discolored foliage in central Virginia suggests several possible causes.

Potential Culprits

• Rust fungus: Orange-brown pustules; remove affected plants, apply sulfur fungicide.
• Root-knot nematodes: Stunted, yellowed plants; solarize soil or apply beneficial nematodes.
• Drought stress: Clay soil dries hard; deep soak weekly.
• Poor drainage: Clay holds water → root rot; improve with compost.

Diagnostic Steps

1. Inspect leaves for rust spores (orange powder).
2. Check roots for galls (nematodes).
3. Test soil drainage: dig hole, fill with water, time drainage.
4. Submit sample to Virginia Cooperative Extension.

General Care

• Full sun to part shade.
• Well-drained soil; tolerates drought once established.
• Can be invasive—monitor spread.

Identify the specific cause before treating; this "carefree" groundcover does have vulnerabilities.