The white cottony substance is on the buds themselves and not necessarily the leaves. I tried mild soapy water and it did not work. What is causing this?
How to Get Rid of White Cottony Substance on Hibiscus Tree
Certified GKH Gardening Expert
It sounds like you have either mealybugs or possibly scales, which are closely related to mealybugs and are an occasional problem on these plants. Neem oil is an effective treatment. Here is more iinformation: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Hibiscus are particularly suceptible to this, and it is an insect, called the "whitefly" that causes it. I have found on the hibiscus I have had in the past, that a mixture Horticultural oil and mild soap water (dawn) sprayed on the affected areas has worked well. I caution you to use the spray in the evening, though, as the suns rays will cause burn spots if it hits the oil.