Now is the time to consider treatment of ponds and lakes to prevent aquatic vegetation from overwhelming the water. If the water had excess aquatic vegetation last year, chances are it will this year as well. Controlling these weeds when the populations are low, before they’ve had an opportunity to greatly expand, makes the job much easier and potentially less costly.
Keep in mind that every body of water needs some aquatic vegetation. As plants they give off oxygen, which fish, being animals, require. Vegetation also provides hiding areas for young fish, protecting them from predators. So don’t create a sterile environment by attempting to control all aquatic vegetation.
But we’ve all seen instances where excessive aquatic vegetation has curtailed enjoyment and usefulness of the pond. I’ve seen a few ponds that appear you could walk on top of them there were so many pond weeds present. All these weeds are a concern for several reasons. First they impede enjoyment of the water as you can’t fish very easily and you certainly wouldn’t have any fun swimming in such an environment. Although I wonder how many kids actually still swim in farm ponds? When I was a kid, several times a week we’d head to the pond to swim and canoe. It was a treat we looked forward to after a morning of walking beans (something I know not many farm kids today have undertaken).
Aquatic weeds can be controlled in several ways. First is to reduce the amount of nutrient runoff into the pond. All plants require fertilizer to grow, and aquatic plants are no different. Reducing nutrients helps control weed growth. A grass buffer strip helps strain nutrients and sediment. If the septic system drains into the pond make sure to properly maintain it.
If the weed population isn’t too heavy, manually removing the weeds can work. Although this control method will require constant vigilance and work. Triploid grass carp (sterile) will help with some weeds. Algae (or moss as many refer to it) is free floating and found in many ponds. Grass carp often don’t control this weed effectively.
In many instances you’ll need to utilize a herbicide to control aquatic vegetation. Copper sulfate works excellent to control algae and fishing or swimming restrictions are minimal (read label). Mixing the copper sulfate in hot water in a plastic container before spraying into the pond and allowing it to sit for half a day allows for better control as the granules mix up better.
Duckweed and watermeal are two floating weeds common to many ponds. Their control is more difficult and requires a more expensive herbicide. All these floating weeds are best controlled when winds concentrate the weeds to one side of the pond. Utilize a pump-up 2 or 3 gallon hand sprayer to treat.
There are other common aquatic weeds including: pond weed, cattail, creeping water primrose, coontail, etc. We’ve an aquatic weed control handout that will help you identify and understand weed control methods that’s available on line at: web.extension.illinois.edu/abhps click on the Local Food Systems/Small Farms icon towards the bottom of the page and look for the link entitled “Managing Aquatic Weeds”. Or stop by your local office for a copy.
One important thing to remember, don’t treat the entire pond at one time. As the plants decay, the organisms responsible will use available oxygen supplies, and this could be very detrimental to the fish, leading to fish kill of the larger fish (which require more oxygen). Treat ¼ or 1/3 of the pond at a time and then wait several weeks before treating more.