I'm inclined to suggest topical applications of imazapyr (POLARIS) for any areas of watershield and nuphar that you wish to control.
For the milfoil, either NAVIGATE (a granular 2,4-D ester) or HARDBALL (a liquid 2,4-D acid/injected sub-surface) should provide decent results when applied while the plant is immature and actively growing.
Either option would require large-area coverage, rather than isolated "spot-treatments", since exposure-time should be sustained for 12-36 hours for optimum results. Such treatments should be made when sub-surface currents are nominal, and no rain-induced influx of water is expected for 48+ hours.
It's unlikely that topical applications of imazapyr would have any notable affect upon DO-levels since its effect on treated plants is very slow.
The potential for DO-issues associated with the milfoil treatments is a little less predictable. Ultimately, such treatments initiated before the plant has developed a high biomass will greatly reduce the potential for DO-issues, especially under cooler spring time water-temps.
I'll email the labels for all three products to you for review. Feel free to reply with any questions.
