Have you used systemic insecticides on it? They do not like that, and that will cause it very quickly. It could be the geminivirus that attacks some forms of hibiscus. It could also be leafhoppers, which are very hard to catch on the plant.

Hi junkyardgirl,

Thanks for replying. No I didn't use insecticides (the most I use very rarely is ivory soap/garlic/oil spray) and I didn't use this near the plant this year. I am wondering if lack of moisture/food could have caused it? Since I've been watering more and fertilizing, fewer leaves are looking bad. It's a huge plant and it's located in a boggy clay soil so I just assumed it gets enough water naturally.

I'm hoping it's not a virus but thanks for the info, I'm going to try and find more info about it.