UPDATE: We will never use Preen again. While it does work, it is very damaging to the environment and the creatures who have to withstand it's toxic ingredients. https://sustainability.energy/is-preen-bad-for-the-environment/
Several old, overgrown rhododendrons having been removed, the slope freshly mulched, we're hoping that the spreading of "Preen" to prevent weed seed germination, will do a good job.