What is wrong with my monstera albo? Please read full details.
I’ve had this Monstera albo since August 2025 and it’s been healthy until recently.
Over the last few weeks, I’ve noticed new brown lesions with yellow halos appearing on multiple leaves. I opted to observe at first as the plant area is regularly maintained with systemic and I have not introduced a new plant to the collection. Existing spots are also enlarging, and it seems like additional existing leaves are developing new spots over time.
Initially I thought it was thrips because I’ve dealt with thrips before and the damage looked suspicious. However:
• I’ve inspected the plant multiple times with a flashlight.
• Checked the tops, undersides, petioles, and stem.
• I cannot find a single adult thrip, larva, or black frass.
• The Monstera growing right beside it just unfurled a completely healthy new leaf with no damage.
• No other nearby plants are showing similar symptoms. In fact the other 2 other monsteras beside it are not exhibiting anything at all.
• I treated my collection with systemic about a month ago as part of routine prevention.
• I water my plants once a week and the foliage doesn't get wet. The roots and stem look healthy.
The lesions are mostly round brown spots with distinct yellow halos. They are flat (not raised), and rubbing the underside does not produce orange/rust-colored powder.
I’m trying to determine whether this looks more like:
• Thrips with an extremely low population,
• Rust fungus,
• Another fungal/bacterial leaf spot,
• Or something else entirely.
I’d really appreciate any thoughts from people who’ve seen this before, as I’d like to identify the cause before deciding on treatment. My plants are regularly maintained and I follow a strict I isolation process when bringing in a new plant (which I have not in that area for a while).
Please be kind, my first time posting here.
Thank you!
(Photos attached.)