Rust
Orange, yellow or brown powdery pustules, mostly under the leaves.
What you'll see
- Powdery orange, yellow, brown or black pustules, mostly on leaf undersides.
- Pale or yellow spots on the upper side of the leaf, above the pustules.
- Rubbing a pustule leaves a rusty smear on your finger.
Why it happens
Rust fungi attack only certain plants. Their spores blow in on the wind and infect leaves that stay wet in mild weather.
How to fix it
- Pick off the first infected leaves promptly; stripping lots of leaves does more harm than good.
- Collect fallen infected leaves and bin them.
- Water at the base, early in the day, so leaves stay dry.
Keep it from coming back
- Choose rust-resistant varieties.
- Space plants for air flow and avoid overhead watering.
- Feed lightly; lush, soft growth is easier to infect.
Sources
General guidance, not a diagnosis. For valuable, edible or outdoor crops, check with a local extension service or plant expert. Use any product exactly as its label says, and keep children and pets away while it dries.