I applied a dose of Sonar RTU last year in my pond and it knocked out the duckweed till today. I noticed a few sprouts around debris in the water, not much.

Now the thing is, I shut off my aerator 2 days ago to see if it helped with water clarity. So I'm wondering if it's related to that. I hate to dose up the water if I don't have to (since it killed everything), but even more than that I hate the thought of having duckweed again.

I figure my options are: 1) nuke the duckweed again with a full dose of Sonar, 2) try a smaller dose, 3) wait and see if the aeration back on is enough to keep the duckweed at bay.

Incidentally I'm planning a alum dose the next time I have a few hours of free time (which could be 2 weeks out). I'm wondering if that may also help knock down the phosphorus enough to keep the duckweed in line. My phosphorous levels are at about 0.05 ppm so a bit high.

Before spending the $$ on Sonar again, I'd try the alum and whack any DW that you see with Clipper. What's your pH?

I feel your pain TSK. Duck weed is a real PITA!

pH is 7.5. I've got alum + lime in my shed (if dropping pH was the question, there will be lime involved). I should mention I do have a quart of Sonar that was extra from last time. That's the amount for a full initial Day 1 dosage.

That pH is good. Clipper doesn't like high pH.

Could you explain Clipper to me? It's been a while since I looked at all these methods. It looks like it's a fairly high priced (similar to Sonar) herbicide. Is it less pervasive than Sonar?

Hopefully when I get out there today, the duckweed won't have spread much but I'll find out shortly. I've been running the aerator since I spotted the weed.

From their website:

"NEW! Looking for a new aquatic herbicide to control tough plants? The newest contact chemistry for the aquatics market, Clipper delivers fast and selective control of tough invasive and nuisance plants such as cabomba, watermeal, Eurasian watermilfoil, water lettuce, duckweed, giant salvinia and more. Plus, Clipper dissipates quickly from the water column and does not accumulate in sediment. And, Clipper offers reduced PPE requirements 51% WDG formulation for easier application and handling."

PM sent.

IMO, Azolla is tougher to control than duckweed - yet Clipper did a great job.
BTW: the shoreline emergent plants were whacked by a prior treatment of diquat that simply couldn't handle the Azolla.

Tilapia if available, does a quick and thorough job on Azolla and Duckweed.
G/

..assuming the residents living around the pond are prepared to bag-up winter-killed tilapia. Makes for a memorable experience.

Aw Kelly, the turtles, coons, and buzzards clean up the ones not harvested - you know nature's clean-up crew...
G/

I can see where Kelly is coming from. When the pond is ringed with houses and manacured lawns, the wildlife stays away.

We have acreage Scott - don't even know any city slickers that have ponds ringed with houses and manacured lawns- not any of my red neck friends...

Will summer stocking of mossambique tilapia get rid of the Azolla problem on my 1/4-acre pond in N. CA? It's in the forest, so I don't have to clean up the winter-killed fish myself. The bears, coyotes, mountain lions, raccoons, ravens, eagles, and minks will do the job. (I'm probably forgetting some.) Since the tilapia will not reproduce (assuming all males), I may have to plan for some summer attrition from kingfishers, herons, and minks. What's the right stocking rate?

Hi T Gray I am in Calif also,lake co.have you checked to see if tilapia can be stocked in California ponds.I don't think they will survive the winter here.

Hey cb100

A lot of folks stock Tilapia in the spring for vegetation control filamentous algae control and table fare, knowing they will die at the end of the summer when the water cools. There are also a lot of folks that stock trout in the fall, knowing they will die the following spring when the water warms.

I considered stocking Tilapia for one year just for fun, but am told it is not legal to stock them in Illinois. CA may also have a restriction.

Thanks for correcting my newbie input Esshup. I thought I had read somewhere that Tilapia was effective at controlling Azolla, Duckweed, etc as well as FA...Lesson learned..will leave the expert input to the experienced guys. My apologies to anyone I may have misled.

Bill D, here is where grass carp may be your answer, besides the Eurasian Millfoil problem you have. For years I have had a tiny area about a yard square of duck weed in my pond but it has never gotten out of hand. I have always guessed that it was because of my grass carp. The problem with grass carp is getting the right amount for the job in the pond. I usually put 6 in at a time and watch for results.

If you will do a Google search you will see that grass carp will eat duck weed but it is not there favorite thing to eat.

John I know nothing about grass carp except what I have read here on PBF. But from what I have read it seems the grass carp work slowly on the problem. So the inclination of pond owners is if they don't see immediate results, they think they need more grass carp. Then they put in too many and in a few years have a pond denuded of vegetation.

Ponds seem to be good (or at least persistent) teachers of patience.

I've put 4 in my old one acre pond as a preventative measure as I know Lilly pads and water primrose are just starting up again after the clean out. Hoping that four is just enough to keep the plants from getting too established but not so much it wipes them all out. Put a couple in my newish 3 acre pond also as a preventative. Don't know if that was the right thing to do or not but will see in a few years.

Hey george1,

Did you mean grass carp?

Bill, they will eat it, but not in all scenarios, and not at all stocking rates.

Usually Tilapia are used for FA control, and Triploid Grass Carp for vegetation control.

Esshup,

Thanks for the clarification.

Both tilapia and grass carp - did a number on it in about two weeks.
G/

Only cold-hardy tilapia are outlawed in our region. Mossambiques are not cold-hardy. I am expecting to restock every year, if I go that route. Azolla is being delivered by ducks and other wildlife from neighboring ponds. I am seeking a management solution that does not harm wildlife.

Is the solution a MIX of tilapia and grass carp? Will either of these fish attack water lilies, cape pondweed, and/or tadpoles?

T. Gray, you may want to define "Cold-Hardy". I know of no "cold_hardy" tilapia species that exists, nor do I know of any Tilapia species legal for release into open waters in California. Open water is defined there legally, as any water, pool, or impoundment subject to weather or any water not being sterilized or entering a municipal treatment plant before being realeased...

I have confirmed that Tilapia are not legal in northern CA. I was misled by some information I found.

Our pond had two fish species in 2010 when I drained it most of the way. I netted fish from the teeming pool at the bottom to have a look. One was orange, about 3" long, a goldfish I guess; and the other was shaped like a bluegill but with a pronounced dorsal bump and only 3-4" long. I probably killed them by reducing their pond to a puddle for several summer months. What were they? The Azolla became a problem starting in 2012, so I guess the fish had been keeping it under control.

Currently I'm on a new tack against my Azolla problem. The water column is very dark with suspended organic matter (confirmed with 400x scope) and starting to go anaerobic. Sediment has dramatically increased over the winter, based on material coming through the pump.

Solving the sediment problem led me to discover biological muck elimination with bacteria, offered by several companies. Does anyone have experience with this?

One company, Clean-Flo, packages aeration equipment with bacteria and enzymes. They suggest that nutrient reduction (from the muck) will control Azolla as well. Is that likely? I had not considered it because Azolla fixes its own nitrogen through symbiosis with Anabaena.

Azolla has accelerated the existing muck problem caused by tree leaves. The trees are cut back, and I hope to manage the muck against future leaf drop using bacteria. There is no other known source of nutrients.

I would contact these people: Bugman

They custom blend bacteria to work the best in YOUR pond. If going the bacteria route, I would do that to give it the best chance of working. But, bacteria is a long term process, it won't be a "quick fix".

For a quick fix, and a long term solution, I would look at hitting it with a herbicide, and starting a bacteria treatment program with the correct bacteria.