Yes, it is possible to use a tow behind sprayer to spray trees, even though most models are not designed for this purpose. In general, even the best tow behind sprayers are designed more for use on lawns than tree-lined areas, but if you can easily and simply maneuver your unit around the trees, the spraying effect can work perfectly well on plantlife of all shapes and sizes. Some of the more high-powered units out there, like the Agri-Fab 45-0293, are among the best tow behind sprayers to choose if you plan on spraying your trees.