I am part of an organization that has a series of 6 small ponds on a trout stream that have maintained healthy fish for over 40 years. Our biggest problem has been Eurasian Water Milfoil and filamentous algae but we have been able to keep both under control using a diquat and chelated copper mix. This year a new fish manager decided to bring in a professional pond management company for consideration of taking over management of the lakes. The company requested that the pond water quality be tested and they would do it for a fee. Three lakes were tested, the uppermost, the middle lake and the lowest lake. All looked good on the lower two lakes but The uppermost lake showed an excessive phosphorous level along with out of acceptable range nitrogen-phosphorous ratio. There was a small forest fire immediately above that lake in 2019 which probably produced an increase in runoff silt combined with ash this past spring. Could this explain the high phosphorous unique to this lake. BTW: even with the high phosphorus, fishing was good in the lake this year and they showed no sign of stress. The tests were done in early October of this year.

It could be.

If you want to kill the EWM in the ponds for possibly up to 2-3 years treat the ponds when the water temp is 55°-60° with a 10 PB dose of Fluridone - Sonar AS or similar product. It will take up to 45 days for the EWM to die, but it will stay dead and the only way you will get more is if some of the seeds in the bottom of the pond germinate. Do that treatment every few years and you will eradicate it from the pond, and at that low dose, the native plants will survive.

I have seen your enthusiasm over Fluridone for sometime and am sure it is a very effective treatment for EWM. Our ponds have streams flowing through them with constant turnover of the water and when I looked at Sonar I became stumped at how it could be applied in our situation. Do you have a solution to the flowing water problem? I started using the diquat/ Cutrine+ method many years ago when, to the best of my knowledge, choices for EWM were 2-4D pellets and diquat. I chose the diquat treatment because these ponds are fished constantly and shutting them down for a lenghty period is undesireable and the stream is used for irrigation on a ranch below our ponds with the possibility of the herbicide being carried downstream is also undesirable. Is Sonar a long term systemic herbicide and can it be used with the restrictions I have mentioned?

Thanks for your reply.

Nope, sorry, that won't work in your application. Both because of the flow through water and the longer dwell time for the irrigation on land.

I like fluridone in the correct application site for EWM and CLPW because of a few things 1) minimal labor to apply 2) Only 1 application is needed 3) when applied correctly, only the invasive plants are affected by it, not the natives.

BUT, it can't be used in all scenarios.