Wait until May, preferably after spring rains have subsided (for these two species). You'll probably have mature DW ad WM still/already on the surface, and newly germinating plants popping every day; which sets the stage for treatment-timing. Ideally, treat before the plants begin to produce more seeds. I didn't read this thread's history; but, if this is your first season to treat, plan to treat again next season (same time) to catch any latent seeds that failed to germinate this season. Breaking the seed-production cycle is critical for long-term (multi-year) results. But, with transient waterfowl and turtles comes the possibility of new plant/seed introductions from adjacent bodies of water. So, no "permanent guarantees" even if you do everything perfectly from a treatment standpoint.
