Which active ingredient should I use to treat my hemlocks?

Most situations require only imidacloprid. However, if the tree has declined in health significantly or the HWA infestation is extremely heavy, an initial treatment with a dinotefuran-based product might yield a better outcome. Dinotefuran is a faster-acting, albeit shorter-lasting active ingredient. You should follow up in a year with an imidacloprid treatment to further protect your tree.