Category Archives: Aquatic Environments
We talk about weed issues in ponds, but another aspect of pond management is fertilization and liming. Haphazard fertilization programs are not recommended in ponds. However, liming every few years has cultural benefits to a pond and keeps the water alkalinity above 50 parts per million (ppm) which is better for certain herbicides.
When the soils become more acid, important pond nutrients like phosphorus (P) is not available to algal production. Phytoplankton are important for fish ponds for the production of oxygen. They also convert nutrients like ammonia, which can be toxic to fish, into a non-toxic form.
We spend a lot of time looking at pond weeds during the summer. When we have filamentous algae, we use compounds with copper. Copper that is toxic to plants and parasites in pond water is also toxic to catfish when the water is very soft. Copper sulfate is an example of these herbicides that is more likely to cause fish toxicity. Alkalinity needs to remain above 50ppm.
If there is no water in the pond, you can do a routine pH test on the soil. But it is not recommended to do a pH test of the water, because pH in water changes during the day. It is better to calculate the hardness of the water. UGA Extension Aquatic Specialist Dr. Gary Burtle has worked with the UGA Water lab in developing a pond water test. In my experience, if the pond has not been limed in a few years, it’s going to need lime. I’ve never seen a test come back that said no lime needed.
Sources of Lime
The real issue is solubility and particle size. Dr. Burtle says most of the lime should pass through a screen size of 200 meshes per inch. Lime larger than 60 mesh is too large; it dissolves too slow. Hydrated lime is a good lime for ponds, because it is more soluble in water than calcium carbonate.
Dr. Burtle recommends apply only 50 lbs of hydrated lime per acre in a single application in order to avoid creating ‘hot spots.’
Method of Application
If no water is in the pond, agriculture lime can be applied on dry pond bottom. Soil test of pH can determine the need.
With water, the worst thing we can do is dump lime in the pond from the edge. It is also not recommended to lime the perimeter of the pond. You need a boat to do it properly. Specialized equipment is also needed to calibrate correctly. Here In the top photo is Alan Dennard and Ken McKinis liming a pond a few weeks ago. They would make several passes over to not create hot spots.
I was talking with Alan Dennard who treats ponds in our area, and like myself, he claimed this season has been lowest calls for pond weeds in a while. We’ve had much fewer pond calls this year for some reason. But lately, I’ve been catching up. The good news is that we are moving back into a period better for treatment of pond weeds. If you treat on your own during the summer, we have to be careful not to cause an oxygen depletion which would kill fish. Treating 1/4 to 1/3 of the weed infestation at a time is recommended.
This week, I looked at a grass I had not seen before. It turned out to be baggy knee grass, one UGA Aquatic Specialist Dr. Gary Burtle says is showing up more and more in South GA ponds. The flower is easy to ID. To the left is a picture of that. The good news is glyphosate has activity on this weed. We pretty much start with this active ingredient for grasses nonetheless. A 2% solution spot spray with a surfactant is the recommended rate.
Behind you’ll also notice filamentous algae. There was also a submersed weed I could not see to identify. We’d have to use copper complex herbicides for algae and diquat for underwater weeds. With temperatures in the upper 80s and low 90s, we still have to take precaution in treating that algae and submersed weeds.
Most filamentous algae control methods are similar, except for a few species. And these are one of them. This is a group of wide-spread algae that are difficult to control. Pithophora and Rhizoclonium are in the filamentous algae category. They resemble a mass of wet-green wool. Control with these types of algae is more complicated than other species.
If you ever see an algae that feels like wool when you pull it from the water, it one of these species. Pithophora may be more common. This is the first time I’ve seen Rhizoclonium. The only difference between the two is microscopic. In the water, we still need to pull samples to determine if it’s pithiphora or rhizoclonium.
Essentially, we can treat these “wool-like algae” the same. Use a tank mix of cutrine plus with diquat at ½ gallon each per surface cre. This pond is very, very small – probably 1/10 of an acre, if that. Weedtrine D is another choice for small ponds. It is a dilute formula of diquat that is about 1/10 the concentration of Reward or generic Diquat which are 2.0 pounds AI per gallon.
Could we use copper sulfate instead of Cutrine Plus?
Yes. This difference is that Copper sulfate is more toxic to fish in soft water. UGA Aquatic Scientist Dr. Gary Burtle says copper sulfate is okay as long as the crystals are dissolved. Add about an ounce of copper sulfate per gallon of water, and get most of it dissolved. We need to avoid using more than 4 ounces of copper sulfate per acre foot of water in a pond like this – which probably has hardness less than 10 parts per million.
I’ve had fewer pond weed calls this year of any. I was talking with Alan Dennard this morning, and he has noticed the same. Last week, I was asked about algae in a pond. Sometimes these small, floating weeds resemble algae from the road. But this is actually duckweed mixed with watermeal. Both of these weeds are commonly seen together. In the morning, they will cover the entire pond. By afternoon, they float around pushed by wind. Oxygen depletion becomes an issue once these weeds take over a pond. There were no fish in this pond, but if this was eliminated all at once, we’d likely see a fish kill. Both of these weeds tend to grow in quiet, undisturbed water.
There are different chemical recommendations for each of these weeds; however, there are also compounds that will kill both however. Both are seed bearing plants, but duckweed is separated from watermeal by its roots. Duckweed has 1 to 3 leaves or fronds with a single root hair coming down. Below is a more up close photo:
The microscope picture below shows the difference in size between duckweed and watermeal.
We would absolutely need to kill only 1/3 of this at a time (if fish are present). Diquat (Reward) has activity on both weeds, as also does Clipper and Sonar.
Some pond scums are showing up after heavy rain from the tropical storm.. There was some in the pond behind our house as well. These blooms usually appear during the summer and fall. We do have to beware of blue-green algal blooms (cyanobacteria). These produce toxins that can be lethal to most fish and livestock. Other aquatic weeds called pond scum are duckweeds and watermeal, Euglena, diatom blooms, filamentous algae, bacterial, protozoan, and zooplankton scums. This photo is likely blue green algae scum which was sent to me last week.
UGA Extension Aquatic Scientist Dr. Gary Burtle says, “The hot temperatures make most algaecide applications dangerous to the fish due to possible oxygen depletion. However, low dose applications of copper may thin this bloom. Try one quart to one half gallon of cutrine plus per surface acre. Then repeat each week to thin the bloom. That would be about 0.2 lb to 0.4 pounds of copper per surface acre. Dilute 1:10 in water for application to the scum.
An alternative is to use sodium percarbonate (many different label names) at 25 lbs per surface acre and repeat weekly. Spread evenly over the pond surface with a granular spreader and boat.”
Here is a yellow flower thing growing by the pond I’ve never seen. It turns out to be Yellow Iris (Iris pseudacorus). It’s an herbaceous perennial with stuff leaves. It reproduces by floating seed and rhizomes. Up North, it is listed as a noxious weed, but UGA Extension Aquaculture Scientist Dr. Gary Burtle recommends leaving a margin of these plants along the shoreline to prevent erosion. The only thing we need to do is mow to leave a 3 to 5 ft strip.