Yesterday I got a call from a close friend asking me for advice on controlling duckweed. Their pond is near Buffalo, NY. The duckweed had recently taken over about half the pond, but was heading towards covering the pond.
I was at a loss for an answer. I've not had to ever control duckweed, but I know it is darn hard to get rid of. I searched the forums and for things written or videos by Lusk. Other than this article by Bob, I didn't find much in the forums going back over 10 years. What I did find wasn't encouraging.
There is a lot here on the subject and you have correctly noted the difficulty of dealing with it.
If you want to save the fish then a combo of methods is best IMO. A contact herbicide followed by a systemic herbicide. You can work in mechanical removal to help the process. Because of its speed and reproductive methods it is hard to overcome.
Hey Ken. Many options exist for managing duckweed, but as Eric mentioned, duckweed's aggressively prolific habits often make it a challenging adversary. From a herbicide-approach standpoint, find out if the pond encounters frequent or constant water flow-through. If it does, it probably is NOT a good candidate for one of the most consistent herbicide treatments; that being one of the fluridone herbicide formulations. A possible alternative is one of the aquatic labeled flumioxazin herbicides, since they accomplish their function with a significantly shorter contact-time; but completely lack the longevity of activity that fluridone affords. Most importantly!!! Be aware that NY State has some of the most restrictive herbicide regulations in the US. I'm not even sure if either of the referenced chemistries are labeled (legal) in NY; so that would definitely be something for your friend to investigate. If herbicides aren't permissible, he may have to resort to mechanical/manual removal - which will require frequent repetition, quite possibly every season since it will be virtually impossible to break the seed-production cycle through harvesting means. Good luck!
Duckweed is my nemesis! yes Sonar and its generics work, but for a large curvy pond like mine it is very pricey. I've had great initial results with clipper. Really took care of my submerged weeds ,but all you need is a tiny bit of duckweed to survive and it takes over the pond in a couple weeks! Now I'm just trying to keep the main fishing and swimming area clear of it. Has anyone had luck with using a strong aerator with a couple diffusers to keep the area clearer?
Your post is exactly why I started this thread. There aren't any easy answers for eliminating duckweed and its close relatives.
Thankfully, I've never personally had to try and eliminate duckweed. However, it doesn't mean I haven't had a lot of issues with duckweed.
I power-washed my aunt's dog after he jumped into a pond covered with duckweed. I didn't let him into my watershed for about two weeks after that adventure.
Aereation would certainly help. The oxygenation from the diffusers would help stir up and eliminate some of the excess nutrients that let duckweed and other water plants flourish.
Chemicals will help kill the duckweed and other vegetation, but the amount of chemicals you will need, could easily contribute to the decomposition of lots of dying weeds. They will take up a lot of oxygen, which may kill many of your fish due to lack of oxygen from the dying plants.
Probably the closest I've come to controlling it, and many other unwanted pond growths, has been cleansing excessive nutrient water inflow.
That obviously is not always easy or possible.
At one horse farm site we cleared the water by landscaping. We moved a lot of dirt to divert runoff from pasture/paddock/riding rings from flowing into the ponds. We dug a trench to bring clean water into the ponds from a creek above the horses. We ran 8-inch PVC pipe. That water is piped into a settlement pond ahead of the main pond. The settlement pond is actually a koi pond with lots of vegetation that takes up nutrients. Its water feeds two other ponds that include grass carp.
It all works. Unfortunately, every situation is different.
Thanks, Ken Trying not to to give up yet. After reading ALOT of these posts I'm Thinking, a Gast 0523 with two Matala or Vertex diffusers? Our ponds is 18-20 feet deep with a mud base. So i'm sure we'll have to put them on a stand of sorts. Do you think these are correct choices?
Ken, I'm going to add on to this thread because of my duckweed situation this year. I'm a little puzzled by it. We've fought FA every season for the first three years on our pond. But this year (finally) not much FA! We are super happy! But....now we've got a huge growth of duckweed occurring. I don't like either one very much, but it's maybe a bit easier to fish through the duckweed. And the wind moves it around better. Just odd to have so much this year. We've had aeration in since spring 2016. Our bottom condition gets better/firmer all the time. We've repaired both the inlet silt pond dams, so are getting less and less direct run in of nutrients. AND, I raised the pond by ~ 24 inches this year, so we have deeper edges with less light penetration to the bottom (e.g. less fuel for the FA). The only additional 'change' from last season was that my pond was drawn down 3 feet for 3 months this winter (for the outlet pipe modification). This meant hard freeze of the edges of the pond that were newly exposed to the air. We've been thinking this was good for FA control. Would it somehow help the duckweed? We got some big rains mid winter and this spring and have been full pool + the new 2 feet all this year. My current speculation is the duckweed is utilizing my nutrient load that the FA used to. If the FA is not around to use it, 'somebody will' I suppose. I am hoping more emergent plants will show up to take up some of the load. My attempt at starting eel grass was not successful. I remain leary of adding a plant that may become a nuisance.
"Politics": derived from 'poly' meaning many, and 'tics' meaning 'blood sucking parasites'.
I can't quite tell if the close-in of purple blooms in the photo is purple loostrife. The leaves don't look quite like purple loostrife -- and for your sake, I hope that is not what it is.
I got invaded by purple loostrife a number of years ago. It is awful. Every year I get as much out as possible by hand-pulling, using my backoe, and with aquaticic chemicals.
As for lilies, there are many that can be grown in sunken pots or mesh bags, and they will not spread and overtake a pond.
I am a big fan of water cleansing plants, especially in settlement ponds at the main water souces today ponds where it is practical. These settlement-capture ponds can become beauitful koi ponds with lots of cleansing plants.
Thought I would just tag onto this thread, hoping for some feedback on a similar duckweed situation. My pond is about 1/4 acre and 10 feet deep, only about 5 years old. Last year it started to develop a duckweed problem and this year it doubled down! I've read this is a signal of an eutrophic condition, but the pond is/was all sand bottom and I'm not sure how it could develop this quickly, it is void of almost all other vegetation. I'm speculating that as the water evaporates, it is being replenished from the adjacent wetland (high nutrient content) and not pulling water up from the water table.
I aerate 24/7, but the pond is 100% covered in duckweed at the moment. Does anyone have any experience with this level of coverage combined with aeration? My hope is that the aeration is enough to avoid a massive fish kill? No signs of one yet, I've added a few pictures.
As for treatment, I currently just don't have the time to attempt manual removal, so I've been reading about Reward (diquat) vs Sonar (floridone). I've heard people having success with Reward, but that it is most effective when sprayed on. Is either herbicide method better for mass surface treatment on a body of water with nearly zero water flow? I'm hoping I can possibly just treat the whole pond as no beneficial weeds have developed yet.
Gravinus my next door neighbor has a small pond with almost zero "flow". It's more of what I call a "tank". He has duckweed this year. Not nearly as bad as you do, but still he wants to get rid of it. I called an online pond supply company and spoke at length with a very informative young man about how best to combat duckweed at my neighbors pond. He talked me into trying a product they sell called Pond Logic "WipeOut". It isn't cheap, but he claimed it is cheaper than other more well known products for duckweed. He said for a smaller pond with little flow WipeOut is a once a season product. My neighbor is pouring Pond Logic "WipeOut" into his pond this week. I will let you know how well it works.
Thanks for the reply and info! WOW, these herbicides aren't cheap!! I never really did any calculations on cost until I looked up the herbicide you recommended. $80 for 4oz, I'm in the wrong business, haha!!
Please do let me know how well that stuff works in that application. I guess $160 to keep the fish happy would be worth it if it works well.
In the last 2 years I have been seeing duckweed pop up on my pond. Considering it is 35 years old and this is the first I've seen it maybe I shouldn't complain. I use a skimmer net because my pond is small enough at under a 1/4 acre, but I think the culprit is nutrients. I do get an inflow most of the year but stocking and building habitat for fish has caused my fish population to bloom so I assume the fertilizer blooms as well. Skimming is easy because the aeration keeps it towards the shore and once you are ahead of it, it gets easier. But as much as I would love to eliminate it completely, without chemicals I don't see how it is possible. It is so easy to miss just a few plants and even if it all is eliminated, the spring duck visiting season surely will bring more.
Since the duckweed is so prolific, netting out a few pounds a day is also a method of removing biomass to keep it from sinking and decomposing on the bottom. I also set up a 6' diameter floating ring and early in the season add 3 or 4 water hyacinth plants. Within a month the ring is full to capacity and when the season is closing I just pull in the floating ring and compost the plants to get the biomass out of the system. Plus up north the cold winters will kill any hyacinths that escape the ring. I do save a few in the greenhouse to overwinter for next year.
Are there any other suggestions for harvestable plants to grow which can be easily removed at the end of the season to help consume the nutrient buildup?
I still do wonder how I escaped the plague of duckweed for so long.