House Plants/ming aralia brown spots (bacterial?)
My ming aralia is about 2 years old, 2 feet tall in South sun and has been thriving until recently when its leaves started yellowing and falling off. I've have many other mings and know they periodically lose leaves, but these leaves are yellowing near the top of the plant. There are some small brown spots on the underside of the leaves that appear to swell/almost small blisters in places. I looked at the brown spots under a microscope and they appear to be within the cells. The areas around the spots are slightly brown and swollen. I'm guessing it's bacterial, but not sure. I've checked the roots and soil, and all seems fine there. No fungus that I could see, and no root rot. I'd appreciate any help with how/what to treat the plant with so I can save it.
It is highly unlikely that your Aralia is suffering from a bacterial or fungal infection. Those most commonly occur in greenhouse production facilities where the environment is kept warm and humid with overhead watering. Plants are also very close together in those facilities.
Scale insects develop hard outer, slightly raised shells that somewhat fit the description you provided. HOwever, scale usually produce a sticky substance called honeydew on the leaves and you did not mention that. In addition, scale scrape off easily with your fingernail and are not part of the leaf tissue itself.
I suspect that the brown spots and leaf yellowing are part of the natural dying back of leaves for non-disease or pest related reasons. As you know, Aralias can be very fussy about watering and temperature changes. Either of these can cause a sudden flourish of leaf discoloration and leaf drop. A single episode of over or under watering or temperature drop is all it takes. This is usually not fatal as long as the problem is corrected promptly.
I don't have a single answer for you, but if you reflect back on recent exposure to cold or under or over watering, that may help you find the answer. Over watering is the hardest to recall because there are no obvious signs such as very dry soil with underwatering. Overwatering is nothing more than keeping the soil just a bit too damp for a long time. So if you are having a hard time making a determination, then over watering is probably the problem. Plants that are struggling and losing leaves use less water than otherwise so it is important to make the appropriate adjustment in your watering routine.
I have written articles on indoor plant pests, diagnosing plant problems, and on Ming Aralia care that I will email for free to you (or anyone else) who emails a request to me at wcreed@HorticulturalHelp.com.
Please let me know if any of this is unclear or if you have any additional questions.
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Will Creed, Interior Landscaper
Horticultural Help, NYC
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