Pachycereus marginatus Gray Patches: Cold or Sunburn?

Two Likely Causes

1. Cold damage: Edges/tips most vulnerable. Gray, hard, dry patches = freeze injury.
2. Sunburn: If planted with wrong orientation (nursery south side not facing south), tender skin burns → gray/white patches + fungal spots.

Diagnosis

• Outdoor plant? Both possible.
• Recent freeze? → Cold.
• Recent transplant without orientation mark? → Sunburn.

Action

• If cold: wait for spring; dead tissue may slough.
• If sunburn: shade cloth on south side immediately.
• Fungicide on spots (copper-based) if spreading.

Critical

Email photos to gregandkat@msn.com for certainty. Orientation at planting is life-or-death for columnar cacti.