Yes, tropical hibiscus can lose a lot of yellowed leaves due to pests such as spider mites as well as other pests like mealybugs, aphids, thrips, etc. It was hard to find anything in the pictures after your cleaning. Many of these pests leave clear, sticky honeydew excrement on top and-or below the leaves, which ants and other pests are attracted to. The sticky honeydew excrement then turns black/brown due to simple opportunistic fungal infections on the honeydew. New foliage can return in a few weeks. In most cases, a strong shot of water, horticultural soap or neem oil is effective in reducing the population. You can also rinse off the plant to get rid of soft-bodied insects, like some aphids. For harder bodied pests, some people use diluted rubbing alcohol sprays (always test in an inconspicuous corner). There are also several insecticides specifically formulated for the pest but identify the pest as best as you can (add pics of the pest or take samples to a local plant nursery. There is also a pest identification forum in Houzz. For spider mites, you will need a magnifying lens to identify them as they are so tiny. For example, there are some white dots in the last picture that could be spider mites, dust or other stuff. The potting soil in picture 2 seems to be a little dry. We are close to the start of warm temperatures so be ready to ramp up your waterings to "summer levels".

is that green stuff holding the trunks together strangling the plant ...

are these the older leaves only ... is any of the new growth affected??

was it in the house for winter.. if so.. when did it come outside ... and did you properly harden it off to sun??

ken

Thank you both for your responses.

Luis - I cannot find any bugs but the plant seems to have the symptoms of spider mites. Your confirmation of the black mess being a sign of spider mites was helpful So far, the "insecticidal soap" has not solved the problem. I read online that insecticide with Abametin is what is effective against the mites but I'm not sure if that will be readily available and is extremely expensive. I will take your advice and take some leaves to the local garden center.

Ken - I will cut the green string off (thank you!) but I don't think it is suffocating the plant. It does seem like it's more of the older leaves being affected. The plant came straight from a grower - it was not wintered inside.

Dawn

I'll keep trying!

The plant came straight from a grower

when did it come from them ... and when did this start ... transport stresses??? .. how was it protected during the move ...

look to new growth to see if anything is currently going on.. rather than something that might have happened back in time ...

all plants shed leaves... and its usually the oldest one ...

ken