Pocket Botanist
Check these first
- Inspect the undersides of the leaves for orange dust.
- Check if the plant is crowded by other shrubs or tall grasses.
- Look for signs of poor drainage around the root zone.
Likely causes
Rust fungus
Most likelyHow to tell: You will see small orange or brown pustules on the leaf surface that rub off like powder. This happens most often during humid or rainy weather.
What to do: Remove and destroy the affected foliage to stop the spread. Improve air circulation around the plant by thinning out nearby vegetation.
Leaf spot disease
PossibleHow to tell: These appear as dark, irregular spots with a yellow halo around them. They tend to show up when the plant stays wet for too long.
What to do: Avoid overhead watering to keep the leaves dry. Clean up any fallen debris around the base of the plant in the fall.
Find out what's wrong with your big bluestem
The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant 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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When to worry
Small amounts of rust are common in late summer and rarely kill the plant. You should worry if the spots cover more than half the foliage or cause the plant to collapse.
Stopping it coming back
Plant your Big bluestem in full sun with plenty of space for air to move between stems. Water at the base of the plant instead of spraying the leaves.
Big bluestem: spots? Check yours with a photo
Every plant is a little different. Take a photo of your big bluestem and Pocket Botanist tells you which cause is most likely, how serious it is, and what to try first. A few checks a day are free. Save the plant and you get care reminders timed for it.
Scan with your phone's camera to get the app
Or go to pocketbotanist.app/get on your phone
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Questions people ask
- Will these spots kill my grass?
- Usually no. Big bluestem is a tough native grass that can handle some fungal pressure without long term damage.
- Should I use a fungicide?
- It is rarely necessary. Good cultural practices like proper spacing and watering at the base are much more effective.
Guides to these causes
More problems with Big bluestem
Back to the Big bluestem guide
This article was generated with AI on from the plant’s care profile and is general information, not horticultural advice. Read about how we build these guides.