I'm battling some submersed plants in my pond and I'm curious how this has worked for those who tried it. I'm battling lily pads/ fragrant water lilies as well as coontail. The lily pads I've had solid success with 2-4d though I'm likely to switch to Imox this year but I wanted to do some damage to the coontail as well. I've got a large private lake with some shallower coves that are loaded with coontail and lily pads. The wind doesn't cause a lot of water churn so I feel this should do well.
I'm curious if I should do a foliare application or weighted hose to put it in the water better for the coontail.
I wouldn't switch. I would continue to use 2,4-D for the lily pads and Coontail. I would mix in a surfactant and some Cutrine Plus (especially for the coontail). If you only want to use one thing to combat both plants I would stay with 2,4-D, mix in some Cutrine Plus and make sure to use a surfactant in the tank mix, especially for the lilies. Lilies are best treated in the Fall when they are taking nutrients down to the roots to prepare for next Spring.
You are trying to use one thing for both and you will not get the results you want with Flumiozazin. Flumioxazin will not work on the lilies like you want it to work, and it's only rated as "good" for working on coontail. To me you are loosing ground on both of the plants if you go that route.
I would use a two pronged approach. I would continue to use 2,4-D with a surfactant for the lilies (it's rated as "excellent" for that application), and while 2,4-D is rated as "good" for the Coontail, Diquat mixed with Copper Compound (Cutrine Plus Liquid) works extremely well on Coontail. Use a weighted hose for the Diquat/CutPlus mix application.
Now what is rated as "Excellent" to work on both plants is Flurdone, but I don't recommend using that just because it cannot be used as a spot treatment and at the rate that you have to use it, it will nuke EVERY plant in the pond. Not to mention the price of it.
As with any herbicide, follow the label rates. Thinking "more is better" will only shock the plants and they won't translocate the herbicide to the areas of the plant that it is supposed to go. You will just give them a haircut and they will start re-growing again shortly.