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Chemical Treatment

What are herbicides and how do they work?

Herbicides work by targeting a component of the plant's biology and either poisoning it or altering that function of the plant so that it can no longer survive. Generally speaking, all herbicides can be boiled down into 2 groups: Contact or Systemic Herbicides.

Contact herbicides work by poisoning the plant or creating a toxic environment within the plant that prevents its survival. Contact herbicides work more quickly and require direct contact between the plant and the herbicide. A surfactant can help by binding the herbicide to the plant.

Systemic herbicides are chemicals that somehow alter the biological functions of the plant causing death. These chemicals mimic certain hormones, regulate the plants growth or inhibit the enzyme production or bleach the chlorophyll of a plant, stopping photosynthesis.

Compound	Type	Primary Use			Mode of Action
Compound	Type	Submerged	Floating	Emergent	Mode of Action
2, 4-D	S	X	X	X	Auxin mimic, plant growth regulator
Bispyribac Sodium	S	X			Inhibits plant specific enzyme (ALS)
Copper	C	X	X		Plant cell toxicant
Diquat	C	X	X	X	Inhibits photosynthesis; destroys plant cell membranes
Endothall	C	X	X		Inhibits respiration and protein synthesis
Flumioxazin	C	X	X		Inhibits chlorophyll production
Fluridone	S	X	X		Inhibits plant specific enzyme, bleaches new growth
Glyphosate	S		X	X	Inhibits plant specific enzyme, EPSP inhibitor
Imazamox	S	X	X	X	Inhibits plant specific enzyme (ALS); new growth stunted
Imazapyr	S			X	Inhibits plant specific enzyme, ALS inhibitor
Penoxsulam	S	X	X		Inhibits plant specific enzyme (ALS); new growth stunted
Peroxyhydrate	C	X			Toxic to algaes
Triclopyr	S	X	X	X	Auxin mimic, plant growth regulator

Table 1: Information on the type of herbicide (C=Contact, S=Systemic), what that herbicide is generally used for and how it works. (Adapted from Getts, et. Al, 2009).

Concerns with using herbicides

As long as the herbicide is applied using label instructions, it is not toxic to any of the aquatic life in the pond. Furthermore, if the proper safety procedures for personal protection are followed, using herbicides to control aquatic vegetation does not pose a threat to the applicator. The label will also give specific instructions on length of time before the pond water can be used for drinking, irrigation, watering, swimming or fishing.

Reading the label information is key to protection of self, environment and agricultural interests. Please see the websites listed under “Concerns with chemical management options” for more information.

How to apply herbicides

Most applications require some knowledge of the pond (size, depth, etc.) to determine application rates. Usually, herbicides are applied on a per-acre or per-acre-foot basis. If you know the acreage of your pond, you can calculate acre-feet simply by multiplying the acres by the average depth in feet. Average depth can be estimated by measuring random depths in your pond and averaging them together. This page from Texas A&M Aquaculture will give you several options for determining the area and volume of your pond.

Below are some useful conversions and formulas for application of herbicides. Using the formulas above and below, along with the label instructions on your herbicide, you should be able to determine how much herbicide to apply in your pond.

Are any special licenses needed?

As long as you are applying the herbicides on your own property, there is no license needed. Please refer to the Kentucky Department of Agriculture’s website or your local county extension agent.

What Chemical Should Be Used?

Different plants respond to different chemicals. First determine what plant you have by referring to the Plant Identification portion of this website, and then use the chart below.

Chemicals used for specific plants or plant types and ratings of their effectiveness (E = Excellent, G = Good, F = Fair, Blank = Poor).

More information about the herbicides

2, 4-D-based chemicals: Includes Navigate and Weedar 64. These chemicals are systematic herbicides that tend to be slowly absorbed into the plant and act slowly.

Bispyribac Sodium-based chemicals: Includes Tradewind. This herbicide comes in water soluble power that should be dissolved in water and sprayed. It is a selective, systematic herbicide that is slowly absorbed into the plant. For out of water applications a surfactant should be used.

Copper-Based Compounds: Includes Copper Sulfate (“blue stone”), Chelated or Compound Copper (Cutrine Plus, K-Tea, Captain,Clearigate). Before using copper is it best to test the pond water’s alkalinity and adjust copper treatments to alkalinity concentrations.

Diquat- based chemicals: Includes Reward. This is a contact algaecide and herbicide. It can be applied directly to emergent plants or applied to the water. If the product is applied directly to exposed plants, a surfactant must be used.

Endothall (Alkylamine Salt of Endothall): Includes Hydrothol 191. It comes in liquid and granular formulations. It is a contact algaecide and herbicide acting quickly to kill plants cells they contact.

Flumioxazin: Includes Clipper. Flumioxazin should be applied to actively growing plants and a surfactant will be needed if the herbicide is applied to foliage of floating or emergent plants. These are water dispersible granules that need to be mixed in water first and then sprayed. The pH needs to be below 8.5 or flumioxazin will rapidly degrade and lose effectiveness.

Fluridone-based chemicals: Includes Sonar, Avast and Whitecap. These chemicals come in both liquid and granular formulas. They are broad spectrum, systemic herbicide.

Glyphosphate-based chemicals: Includes Rodeo, Aquamaster, Eraser AQ, Touchdown Pro and Aquaneat. These are systematic herbicides that act slowly as they are absorbed into the plant. For emergent plant applications a surfactant can be added for better results.

Imazamox- based chemicals: Includes Clearcast. These are systematic herbicides that act slowly as they are absorbed into the plant. For emergent plant applications a surfactant can be added for better results.

Imazapyr-based chemicals: Includes Habitat. It is a systemic herbicide that is effective at low-volume rates. Imazapyr based chemicals require the use of a spray adjuvant when applying to post-emergent vegetation.

Penoxsulam-based chemicals: Includes Galleon. This chemical can be applied directly onto emergent plants or applied to the water. For applications onto emergent plants, surfactant is needed. Penoxsulam chemicals are broad spectrum herbicides that are slowly absorbed to the site of action.

Peroxyhydrate (Sodium Carbonate Peroxyhydrate) chemicals: Includes GreenClean, PAK27, and Phycomycin (or other chemicals where hydrogen peroxide is the active agent). These pelleted contact herbicides control blue-green algae; they are not effective on the macroalgaes, Chara or any higher plants.

Triclopyr based chemicals: Includes Renovate. These are systematic herbicides that act slowly as they are absorbed into the plant. For emergent plant applications a surfactant can be added for better results.

Copper Based + Diquat: a mixture of a liquid copper based chemical (like Cutrine Plus) with a diquat based chemical (like Reward) usually in a 1:1 ratio. This mixture works by first killing the algae that typically grows on the plants and then the plant itself.

Concerns with chemical management options:

Oxygen depletion can occur after treatment due to the decomposition of dead plant material. This can kill fish in the pond. The best way to avoid this depletion is to treat the pond in sections and let each section decompose for about two weeks before treating another section.
Determination of area or volume of the pond is critical to proper application of aquatic herbicides. Please see this page from Texas A&M Aquaculture for help in determination of area or volume.
Always read and follow all label directions concerning application rates and time for the aquatic plant you are treating. The label will also have specific water use restrictions if they exist.

For more information concerning the labels, Safety Datasheets or general information about the herbicides check out the following links:

MsdsOnline.com

http://www.cdms.net/LabelsMsds/LMDefault.aspx

http://dnr.wi.gov/lakes/plants/factsheets

What About adding a surfactant?

Some chemicals need an additive to make the plant adhere to the leaves of the plant in order for the chemical to work. This additive is called a surfactant and when added to the application mixture (herbicide and water) it allows the herbicide to remain in contact with the leaves long enough for the plant to absorb the herbicide. As a general rule of thumb it is always a good idea to add a surfactant when treating any plants that stick out of the water, such as emergents or non-rooted floating plants.

Surfactants can be purchased at about any farm supply store.