Pond weeds prove a particular challenge

Published 7:45 pm Friday, April 5, 2019

By Terry Rector

Last week, I acknowledged personal experience with some of the challenges that come with owning a fishing pond.

I told about the collapsed spillway, gators and a beaver, and fish killed by a pond turnover.

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In ponds, unwanted plants are weeds, the same as unwanted plants in lawns, gardens and pastures.

And like in those places, a few scattered weeds are harmless, even if unsightly.

Biological control of water weeds would be ideal, but the vegetarian amur carp fish only feeds on a few submerged pond weed species.  For years, I considered myself fortunate because my only serious pond weed problem was water primrose. This one stays rooted in shallow water but sends its branches out to float on the water.

Left alone, primrose can cover up quite a bit of pond surface by mid-summer. It is really not a threat to fish, but neither baited hook nor artificial lure is going down where primrose covers the water.

My good fortune is primrose control is easier and less expensive than dealing some of the other vegetation species. Most weeds that are rooted and grow from the pond edge can be controlled with cheap herbicides like glyphosate and 2,4 D applied from the bank.

Plant species that grow submerged in deep water require a lot more work and expense to control. Ditto for aquatic algae such as commonplace filamentous algae.

So I’ve had no complaints about hooking up my homemade sprayer every spring to keep water primrose down to tolerable.

The pond weed that probably causes the most frustration in local ponds is duckweed. The tiny single leaf plants float and dangle likewise tiny roots downward.

It can cover an entire pond and thick, prolonged duckweed infestations can block sunlight from getting down into the water where it is needed for photosynthesis within the microscopic plankton.

We want pond water green with plankton and sunlight-driven photosynthesis generating the oxygen fish must have.

Watermeal is not a duckweed but is even smaller and often occurs with duckweed.  It looks like merely a seed and there are no roots hanging from it.

Watermeal is the species that showed up on my pond last summer for the first time. It did create a thin layer across the entire surface but moved around with the wind.

Wintertime and lots of water flushing from upstream and out the drainpipe has the pond looking pretty nifty right now. But I know a “seed” or two of watermeal likely survived somewhere in the mud.

If so, warm weather will have it multiplying like crazy. Plus, it got in the first time last year from somewhere and that could obviously happen again.

There is a herbicide control for duckweed. It has two drawbacks. It’s really expensive and watermeal control requires an extra strong dose of it. North of $500 per acre just for the chemical would give control for only this one year. I’m thinking on it but mostly waiting to see if perhaps watermeal is a no-show this year.

Terry Rector is spokesman for the Warren County Soil and Water Conservation District.