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Identify by symptom

What are the orange spots and pustules on my leaves?

Raised orange, yellow or rust-brown pustules that leave coloured dust on a finger are rust fungi. They are host-specific, several need a second and completely different host plant to complete their life cycle, and that is why a rust can appear every year with no obvious source in your own garden.

The one observation that decides it

Note which side of the leaf carries the pustules and what the plant is. Powdery pustules on the UNDERSIDE with yellow speckling above is common rust, and it is the usual answer on leeks, garlic, roses and beans. Bright orange spots on the UPPER surface of an apple or pear leaf that later grow horn-like tubes underneath are cedar-apple rust or pear rust; those need a nearby juniper, so the cure is a survey of the neighbourhood rather than a spray.

Start from the plant in front of you

4 things it could be

Ordered by how much they can cost you — if the first entry fits what you can see, rule it out before considering the milder ones.

  • Cedar-Apple RustFungal diseasesModerate

    Bright yellow-orange spots on apple leaves and fruit that develop tube-like structures beneath; on junipers, brown galls produce gelatinous orange horns when wet.

    Conditions: 8–24°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 days

    Seen on: Apple trees

  • Pear RustFungal diseasesModerate

    Bright orange spots with a red rim appear on the upper leaf surface from late spring. By late summer each spot develops a cluster of brown, horn-like outgrowths on the underside. Heavily spotted leaves drop early and the tree loses vigour.

    Conditions: 12–24°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 days

    Seen on: Pear trees

  • RustFungal diseasesModerate

    Yellow, orange, or rusty-brown powdery pustules on leaf undersides with yellow speckling above; severe infection causes leaf drop and weakened plants.

    Conditions: 10–24°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 days

    Seen on: Beans, Leeks, Garlic, Broad beans, Sweetcorn, Asparagus and 9 more

  • OedemaPhysiological disordersMild

    Small water-soaked blisters on the undersides of leaves and on stems, which later turn tan or rust-coloured and corky. Affected leaves may yellow and drop. The bumps do not rub off and no fungus or insect is present.

    Conditions: ≤18°C · humidity ≥85%First move: Fix the cause, not the leaf

Other symptoms