Cereus chalybaeus Decline: Webs, Yellowing, and Natural Aging

Web Diagnosis Unclear

Photo insufficient for spider mite confirmation. However, yellowing, softening, falling arms on a large mature plant suggest:

Primary Cause: Size Management

• Large columnar cacti naturally shed/lean as they outgrow support.
• Pruning prevents this; cut arms can be rooted.
• Propagation guide linked for reusing pruned material.

Secondary: Possible Pests

• Webs could indicate spider mites—treat with insecticidal soap if confirmed.
• Inspect with magnifier for moving specks.

Action

Prune to manageable size, root cuttings, monitor for pests. North-side Phoenix placement with good drainage is correct.