Has anyone had problems with white furry bugs on hibiscus? They kind of look like a giant version of mealy bugs - up to about 6mm in length (?some longer), white and fuzzy. Tbey like to congregate in the angles between leaves and branches. I've tried good old white oil and pruning off affected branches, but they just seem to be everywhere. I'm not afraid to use something systemic. Any ideas? The plants are still alive, but don't look very happy!