Black Powder on Mower Deck: Smut, Sooty Mold, or Just Dust?

Ohio, dry weather. Fine black powder accumulates on mower deck after cutting. Mold? Fungus? Common in drought?

Two Likely Causes

1. Smut disease: Fungal spores (black powder) on grass blades. Hard to control; resistant varieties are long-term fix.
2. Sooty mold: Grows on insect honeydew (aphids, scale). Requires prior insect activity. Check leaves for sticky residue or ants.

Dry Weather Dust

Could also be fine soil/organic dust kicked up in drought. Wipe a blade: if it smears black, it's fungal/insect. If it brushes off gray, it's dust.

Action

• If smut: overseed with resistant cultivars in fall.
• If sooty mold: treat insects (soap, oil, systemic).
• If dust: ignore—harmless.

Identify the source before treating.