Category Archives: Aquatic Environments

Oxygen Depletion Causing Fish Kills

FishKill

A grower called me to look at a pond in the middle of a cotton field where fish had been dead a few days. There are a mixture of bass and bream that have died. I asked which fish died first, and he said the larger fish. Fish kills can often be associated with chemical runoff or oxygen depletion. When larger fish die first, it is generally the result of some kind of oxygen depletion, since lack of oxygen would affect larger fish first. UGA Extension Aquaculture Specialist Dr. Gary Burtle said there have been several fish kills related to low oxygen in south Georgia in the past week. With rain comes cloudy weather and low oxygen has been a problem recently. Below is what Dr. Burtle has to say:

FishKill (3)“The usual reason for fish death after rains is a partial oxygen depletion caused by the influx of water which has no algae in it or a high concentration of bacteria in it.  When algae are replaced by bacteria, the water turns brown in color and oxygen concentration drops. Bass are larger than bream, so may be affected first. The oxygen stress may cause the fish to become susceptible to disease, so fish deaths may occur for several days after the partial oxygen depletion.

When the pond begins to ‘green up’ again, oxygen concentrations will increase and fish deaths stop. Until oxygen concentration returns to normal levels, low oxygen each morning or during cloudy weather may cause more fish stress and death. The solution is to install an aerator and operate during cloudy weather, which seems to be more prevalent in Georgia in the late summer and fall.”

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Pond Weeds – Creeping Rush

CreepingRush (3)

Here is a pond weed that was showing up a few weeks ago. It seemed to appear in flushes. The day we checked it, the weed was hardly showed up in the pond. It turned out to be creeping rush. Generally, we start with herbicides to control pond weeds followed by stocking carp to further control.

Creeping Rush

Creeping Rush

UGA Extension Aquaculture Specialist Dr. Gary Burtle says creeping rush can look like a sedge, but is a flat stemmed rush in the Juncus genus. Treat with diquat to burn back, and then stock 10 grass carp per acre (triploid and 1 pound each).  Diquat is used at 1 to 2 gallons per surface acre over the infested area.

During the hot months, treat ¼ to 1.3 of the pond area per treatment to reduce the risk of oxygen depletion.  Aeration is also recommended.

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Algal Blooms In Ponds

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We’ll notice pond water color turning a yellow-green when pollen is shed. We looked at a pond last week that had the same color but was result of phytoplankton bloom instead. UGA Extension Aquaculture Specialist Dr. Gary Burtle says this about algal blooms:

“The yellow-green color is normal for a mix of plankton found in fish ponds.  The bloom shows signs of fertility, either from addition of fertilizer or from watershed runoff.

Aerial images look blue due to the reflection of light. Blue is a shorter wavelength and is not absorbed as much as red and yellow, so is reflected. Particles in the water may scatter light so that a different color is observed. However, when the particles are deep in the water, aerial photos do not capture their effect, only the blue or blue-black color. Water color can also be different from different angles, due to refraction.

The aerial photos posted on the web are taken at different seasons.  One taken in the winter may not indicate a pond algal bloom, but one taken in midsummer might capture the bloom.

We recommend that visibility between 12 and 18 inches is optimal for sport fish pond management. Dense algal blooms and scums may occur when visibility is less than 12 inches. Measurements of visibility are taken at the pond surface rather than from a distance. Efforts to correlate light reflection to water quality have shown some interesting correlations, but require special filters and photographic techniques.”

Although fertilization can increase fish production significantly, it is not the best management practice for every pond. Here is a publication on Pond Fertilization & Liming from UGA Warnell School of Forest Resources.

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Pond Weeds – Filamentous Algae

Torpedograss & Filamentous Algae011

I was asked to look at a pond on the Thomas/Brooks line with weed problems. There was quite a bit of torpedograss along the edge. However, we are starting to see algae show up in ponds. Copper complexes are good control options for all algae. Diquat also works well with filamentous algae. This pond has already been treated. UGA Aquatic Specialist Dr. Gary Burtle says one thing to remember is that these herbicides last for about a week, then algae may regrow. For this reason it is recommended to also stock grass carp at 10 per acre to maintain control.

It is still very hot and with fish in ponds, it is best to either treat after we start to cool in the fall or treat very small sections of the pond at each time. Treatment will control the torpedograss for a month or more. Retreatment my not be necessary this late in the summer, but torpedograss treated with glyphosate in early summer will require another application. Use a 2% solution of glyphosate and an adjuvant (surfactant or sticker/spreader).

Filamentous Algae 010

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Pond Weeds – Torpedograss & Southern Water Grass

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Torpedograss

Torpedograss

We looked at a pond yesterday which was about 1.5 acres, spring fed and covered in some weeds. Weeds in ponds are placed in one of three categories: submersed, emersed, or floating. These weeds were coming from the bottom of the pond and sticking out, which are emersed. UGA Extension Aquaculture Specialist, Dr. Gary Burtle, helped us ID the weeds. The short weed is southern water grass which has some emergent parts and some submerged parts. The other plant is torpedograss. It is the tall grass with the panic-grass seed head.

Southern Water Grass

Southern Water Grass

Both weeds respond to glyphosate if enough of it is emergent in order to obtain a good treatment.  Dr. Burtle says one problem is that glyphosate does not seem to translocate into the underwater portion of plants as well. If the weed is submerged more than 25%, the herbicides have less effect. For this reason, tt is recommended to use a sticker/spreader adjuvant, like a crop oil. Also, stocking 10 grass carp triploids per acre after the weeds have decomposed would help.

This pond does have bass which is very risky to treat during hot time of the year. As the plants decay, fish can die from result of oxygen depletion. Instead of treating the entire pond at one time, it is best to treat 1/3 or 1/4 sections at a time.

 

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Pond Weeds – Southern Naiad

Southern Naiad 004

Friday morning I stopped by and looked at some pond weeds that have taken over a small pond. In terms of pond weed control, we generally use herbicides first to get the problem under control. The weed we identified was a submerged weed called, southern naiad, Najas guadalupensis. Leaves are dark green to greenish-purple, ribbon-like, opposite or in a whorl of three, mostly less than 1/2 inch long and 1/8 inch wide.

Southern Naiad 009Is it temperatures too warm to treat? Temperatures are starting to get warm for treating ponds. Because we are not yet in the  hottest part of summer, treating small sections of the pond will lessen the effect of oxygen depletion. Below are some specific recommendations from UGA Extension Aquatic Specialist, Dr. Gary Burtle:

Since the pond is heavily infested with this submerged weed,  treat ¼ to 1/3 at each herbicide application and waiting 5-7 days before the next treatment.  This method reduces the risk of depletion of dissolved oxygen and allows for herbicide application when water temperatures are hot.  It is always a good idea to have an emergency aeration  plan to use when applying aquatic herbicides.

Since these herbicides have no residual effect, repeat application may be needed or grass carp should be stocked to prolong control of southern naiad.  After the initial herbicide burn down, stock 5 to 10 grass carp per surface acre of the infested area.  Use triploid grass carp that are about 1 pound or are 14 inches long in order to avoid predation from largemouth bass in the pond.

Southern Naiad 007

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Pond Weeds – Parrotfeather

Parrotfeather 001

Brooks County Ag Agent, Garvie Nichols, and I talk about the number of pond questions we receive. The most common pond question I receive pertains to weeds. Generally, pond weeds are treated in the spring and fall. Here is a weed I DanParramore-Parrotfeather 004looked at this morning which turned out to be parrotfeather. This plant is also used as an aquarium plant. It is a rooted, submerged perennial plant that usually grows in shallow water. At its base the internodes are longer, and they shorten towards the tip.

It is better to start with a herbicide to manage pond weeds, and sometimes follow up by stocking grass carp. UGA Extension Aquaculture Specialist, Dr. Gary Burtle says that 2,4-D, triclopyr, or imazamox are good chemical for control of parrotfeather.

“Navigate and Weedar 64 is a granular butoxyethyl ester of 2,4-D and has been effective on parrotfeather. 2,4-D compounds are systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.

Parrotfeather 003Reward is a liquid diquat formulation that has been effective on parrotfeather and is very effective if mixed with a copper compound. It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact.”

If there are fish in the pond, it is also recommended to treat small portions of the weeds (1/3 at a time) to reduce the risk of oxygen depletion.

Here is a link to the Aquatic Environments section of the UGA Pest Management Handbook which shows weed control options for pond weeds.

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