Is this fungus going to kill my plant?

Usually not, but it is unsightly and can reduce the plant's vigor. Managing the environment helps keep it under control.

Should I use a fungicide?

Fungicides are rarely needed if you practice good garden hygiene. Focus on airflow and watering at the soil level first.

What are these spots on my New England Aster leaves?

Check these first

Inspect the undersides of the leaves for orange spots.
Look for a white powdery substance on the leaf surfaces.
Check if the plants are crowded together.

Likely causes

Rust
Most likely
How to tell: Small orange or brown pustules appear on the undersides of the leaves. The leaves may eventually yellow and drop.
What to do: Remove and destroy the infected leaves immediately to stop the spread. Avoid overhead watering to keep the foliage dry.
Powdery Mildew
Most likely
How to tell: A white, dusty coating appears on the surface of the leaves. It often starts during humid weather.
What to do: Improve air circulation by spacing plants further apart. You can apply a neem oil spray if the infection is widespread.

When to worry

Minor spotting is common in late summer, but heavy infection can weaken the plant. Remove severely damaged foliage to protect the rest of the plant.

Stopping it coming back

Water at the base of the plant rather than over the leaves, and ensure there is plenty of space between plants for air to move.

Not sure which one it is? Photograph your new england aster.

This page lists the usual causes. Pocket Botanist looks at your actual leaf and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.

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Questions people ask

Is this fungus going to kill my plant?: Usually not, but it is unsightly and can reduce the plant's vigor. Managing the environment helps keep it under control.
Should I use a fungicide?: Fungicides are rarely needed if you practice good garden hygiene. Focus on airflow and watering at the soil level first.