Boxwood Decline: Yellow Powder Is Likely Pollen, But Check for Root Rot Fungus

Thick Yellow Powder on Dying Boxwood Branches — What Is It?

Your boxwoods show slow dieback with heavy yellow granular coating on affected areas. No movement — not insects. Insecticide didn't help.

Two Likely Causes

1. Pollen dust from nearby trees (pines, oaks) — coats leaves, washes off. Harmless.
2. Boxwood Decline — a soil-borne fungal complex (Phytophthora, Volutella, etc.) that kills branches one by one. No cure.

How to Tell

• Rub the powder — if it smears like dust, it's pollen.
• If it's stuck, crusty, and branches die progressively from tips inward → Boxwood Decline.

Management (If Decline)

• Prune out dead branches (sanitize tools).
• Drench soil with 2% Daconil (chlorothalonil) — may slow spread.
• Improve drainage, avoid overhead water, don't overmulch.
• Consider replacement with resistant cultivars (e.g., 'Green Velvet', 'Winter Gem').

Pollen washes away; decline is permanent. Check after rain — if powder gone, you're lucky.