There’s a question I get at this time of year which comes up often enough for me to want to address it here. And that is, “What should I treat duckweed, or other pond weeds with as we come into late summer and fall?”
It’s a reasonable question and one that deserves an honest and reasonable answer, which is…
Nothing at all.
I suggest to all of our clients that late season duckweed or weed problems are unfortunate but mid to late summer, or fall, is not the time to treat them. Particularly as the seasons get cooler, many of these aquatic weeds will go away all on their own. So a bit of patience can save you a lot of money if you’re smart about it.
For the most part we have to treat these unwanted issues with chemicals if they are present and growing. It’s the best way to manage them effectively. However many of these plants get harder to control as the season progresses and by mid summer, while they can be knocked down, you’ll use a lot of “treatment” to do it and still possibly get marginal results. Also there’s a greater risk of losing fish from the die off and low oxygen levels…which is also made worse by the normally hot conditions of summertime.
This does not mean of course that there isn’t work to be done on improving the condition of the pond. Some of these plants opportunistically grow because of high nutrient loads in the water, or heavy muck at the bottom. Both of these things can be addressed, over time, with beneficial bacteria treatments. And as the pond get’s cleaner, unwanted growth just has a harder time of taking off.
So When Is The Best Time To Treat Duckweed Or Aquatic Weeds?
It’s simple really. To get the best effect and control on these various pond weed species, you want to treat them early on in their growth cycle, as they are starting to show up. This is normally in the spring time or early summer. The weather may be a bit cooler then too so you have the added advantage of more favorable weather, and you won’t normally have to use as much product to chemically treat the problem. This varies, depending on what you need to use, but if you can apply the aquatic herbicide topically rather than dose the entire pond volume with it, that’s just a better route to go for the environment if you ask me.
It’s interesting that one of the most controversial videos I’ve ever done has been on duckweed control. The comments were quite varied, with some people being very critical of using any chemical at all, or wondering why anyone would even want to remove duckweed. I suspect that many of these folks had smaller ponds where duckweed is actually used and managed to good effect. Some fish eat it, and it provides shading and some natural enhancement to a small pond. For large pond owners however it can be really problematic and irritating. And in many cases, unless someone is willing to get ahead of it and clean their pond up biologically, then a chemical treatment may be one of the options they could choose…like it or not.
What is really important though is to use any pond treatment judiciously. It’s silly to just start dumping things into the water like Round Up or what-have-you, just hoping it will work. Where aquatic weeds are concerned, you want to do some research, figure out what you have, and then treat accordingly, at the appropriate time. That will give you the best control results, with a minimal effect on the environment.
There are also possible options for various weeds that don’t involve chemicals at all. Some may be more applicable than others. For instance, Talapia (you know the tropical fish that so many people like to eat), are actually great at controlling duckweed when they’re stocked in appropriate amounts. You also can use a homemade duckweed skimmer that makes manual removal a bit easier.
Weed cutters and pond rakes make removal of some of the plant growth a bit more manageable and can give you a good workout while your at it. And this approach is about as environmentally friendly as you can get.