Diagnose by symptom
Rust spots and pustules
Orange-brown, rusty spore clusters on leaves are rust fungi. Most often:
Diseases
Frequently asked questions
What are the rusty-orange spots on my leaves?
This is rust – a fungal disease forming rusty, orange or brown spore pustules, usually on the leaf underside, with yellow spots on top. The dusty pustules spread easily by wind and water splashes to other leaves. Rust worsens in warm, humid weather with poor air movement.
Does rust spread to other plants?
Rust spores spread easily by wind and water, but most rusts are specialised and attack only certain species or plant families. So rust from a rose will not usually move to beans, but it will infect other roses. Promptly removing infected leaves limits spread among susceptible plants.
How do I control rust on plants?
Regularly remove and discard infected leaves rather than composting them, and clear fallen leaves in autumn where the fungus overwinters. Water at the base and provide air movement so leaves dry quickly. Under heavy infection, a fungicide containing e.g. tebuconazole or copper, used according to the label, helps.