Pocket Botanist
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Check these first
- Inspect the base of the leaves for chewed edges.
- Look for slimy residue on the foliage.
- Press on the rhizome to see if it feels mushy.
Likely causes
Iris Borer
Most likelyHow to tell: You will see jagged holes in the leaves and slimy, chewed areas near the base. If you dig slightly, the rhizome may feel soft or hollowed out.
What to do: Remove and destroy any infested leaves or rhizomes immediately to stop the spread. Apply a beneficial nematode treatment to the soil in early spring to kill larvae before they enter the plant.
Slugs and Snails
PossibleHow to tell: These pests leave behind irregular holes and shiny slime trails on the leaves. They are most active at night or during damp weather.
What to do: Hand pick them off the plant in the evening when they are active. You can also place a shallow dish of beer near the base to trap them.
Find out what's wrong with your yellow flag iris
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.
Scan with your phone's camera to get the app
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When to worry
If you see the entire plant collapsing or the rhizome is completely hollow, the infestation is likely too far gone to save.
Stopping it coming back
Clean up all dead foliage in the fall to remove overwintering eggs and larvae.
Yellow flag iris: pests? Check yours with a photo
Every plant is a little different. Take a photo of your yellow flag iris 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
Get the app · Or check it from a photo now, free
Questions people ask
- Can I use chemical sprays?
- Systemic insecticides are generally not recommended for water plants as they can harm aquatic life. Stick to manual removal or biological controls.
- Will my iris recover?
- If you catch the borer early and the rhizome is still firm, the plant will likely bounce back with new growth next season.
Guides to these causes
More problems with Yellow flag iris
Back to the Yellow flag iris 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.