Solving Lawn Rust and Carpenter Ants: Cultural Practices and Targeted Control

A homeowner sees orange rust powder on shoes and mower, plus large black ants climbing brick walls and entering the house on a wooded 2-acre lot.

Lawn Rust

Rust appears as orange/yellow spores on blades in late summer/early fall during dry, cool nights with heavy dew. It thrives on slow-growing, nitrogen-deficient turf.

Management

• Water deeply early in the day so grass dries quickly.
• Mow regularly at proper height; recycle clippings.
• Apply slow-release nitrogen in early fall; don't overdo it.
• Improve air flow and light by pruning trees/shrubs.
• Apply winterizer fertilizer (24-3-12) around Thanksgiving.
• Fungicides rarely work on home lawns; focus on culture.

Rust often fades as fall growth improves.

Carpenter Ants

The "big black ants" are likely carpenter ants nesting in wood (trees, structures). They don't eat wood but excavate galleries. Control requires locating and treating the nest.

See OSU Carpenter Ant Fact Sheet for detailed identification and control methods.