Some flower buds on a hibiscus tree are covered in slightly sticky, tiny gray/brown insects, which are eating the petals. How can I rid the tree of them? Thank you! - Keith
From your description it sounds like you are dealing with aphids on the hibiscus tree. The sticky substance is their frass, aka honeydew. You may also see ants present as they feed on the honeydew and often harbor the aphids.
Your first line of defense is a strong jet of water to knock the aphids and their eggs off the plant, both on top of and under the leaves. It may seem weird, but the aphids have a hard time climbing back up. Next spray with an insecticidal soap, or horticultural oil, being sure to cover both sides of the leaves. Follow label directions carefully, with special reference now to maximum temperature for application. Reapply every few weeks to make sure no eggs have hatched. Hope this helps.
- Carole, Johnson County Extension Master Gardener