CHEMICAL CONTROL OF NUISANCE POND AND LAKE WEEDS

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Aquatic plants are a normal and beneficial part of a lake or pond ecosystem. They provide food, directly or indirectly for all of the animals that live in or are associated with aquatic ecosystems, including insects, fish, waterfowl and other types of wildlife. Plants also provide refuge for small fish from predators, are a source of oxygen, and help reduce erosion of the shoreline by reducing turbulence from wind and wave action and boat wakes. However, when aquatic plants become too abundant and interfere with pond and lake recreation or esthetics, they become a nuisance. Usually the first question asked by pond and lake property owners experiencing aquatic plant problems is "What chemical can I use to kill the algae (or weeds)?" The answer to this question, unfortunately, is not as simple as it may seem.

Aquatic plants require light, warm temperatures, water and nutrients for vigorous growth, just like terrestrial plants. If you have adequate levels of these plant requirements, aquatic plants will grow. Aquatic plant growth is affected by the soil type and water depth but is accelerated by chemical nutrient input to lakes and ponds. These increases are most often a result of human activities such as runoff of lawn fertilizers, agricultural runoff, drain tiles, septic systems leakage, erosion due to construction, etc. This process is called "eutrophication," which means over-feeding. The chemical nutrient of primary concern is phosphorus. The only long lasting cure is to bring waste discharges, disruptive land uses and other nutrient sources under control. But the necessary alteration of the surrounding human community can take many years and in some instances may be impossible. In the meantime, algicide or herbicide treatments are a band-aid approach to consider in contending with the algae or weed problem.

Although the use of aquatic algicides and herbicides can have the advantages of convenience, low initial cost and avoids some of the shortcomings of harvesting (hard work, frequency of treatment, weed disposal, fragmentation and spreading Eurasian watermilfoil, etc.), they have the following drawbacks:

• Algicides and herbicides kill plants without removing them from the water. The material sinks after dying. Its decay consumes oxygen, which could result in a fish kill, and releases nutrients stimulating new plant growth. Formation of lake sediments may be accelerated by chemical treatments.
• The treated plants may disappear slowly from the treated area. Ten days to two months may pass before the nuisance plants sink away.
• Beneficial plants may be killed as well as the nuisance plants. Each algicide and herbicide may kill several or many kinds of plants.
• Algicides and herbicides can drift beyond the point(s) of application. Even lakes that appear placid may have currents making it impossible to confine herbicides to a localized area of a lake without cumbersome physical barriers. In lakes with significant currents, chemicals may be diluted before the desired treatment effects occur.
• Lake owners and users seem increasingly concerned with the perceived risks of algicide and herbicide use.
• Areas may be closed to swimming, fishing or other uses for one to several days or even weeks depending on the chemical.
• The killed plants are often replaced by other forms of vegetation, annoyingly soon in some cases. Less than a month after treating rooted plants, the area may become clogged with masses of stringy algae. Algae may reappear in 10-14 days after an algicide treatment. As long as light, warmth and nutrients exist in a lake, nature will strive to fill the water with some form of vegetation.
• Treatment costs and efforts are recurring, in most cases annually or even more often. The expenditures must be repeated for as many years as control is desired, for centuries if need be, until the nutrient sources of the problem are abated by some other means. Costs for herbicide treatments can be substantial, depending on the type, frequency and the amount of chemicals needed.
• Keeping these limitations in mind, chemicals may still be the best band-aid for your weed control problems. You must ask your-self the following questions to determine what and how much chemical to use.

1) Is a Michigan Department of Environmental Quality (DEQ) permit required?

• The use of chemicals to control nuisance aquatic plants in Michigan is regulated by Act 368 of 1978. The law allows lake and pond front property owners to control nuisance aquatic plants on their property under permit from the DEQ if certain conditions apply. A DEQ permit is required to add any chemical to a body of water if:
• The body of water is not entirely private or is under joint ownership. The body of water drains at any time of the year into another body of water (drain, creek, stream, river, pond, lake, etc.). The body of water is 1 0 surface acres or larger.
• You can obtain Applications for Permit for Chemical Treatment to Control Nuisance Aquatic Plant and/or Algae Growth from District DEQ offices or from: Inland Lake Management Unit phone: (517) 373-8000 Land and Water Management Division 116 Allegan Street, P.O. Box 3458 Lansing, MI 48909
• The best time to apply for a permit is early in the year you propose to treat your pond or lake. Permit processing begins in January. Failure to obtain a DEQ permit when required is a misdemeanor Permits are used as a means of recording usage and improving treatments. It also provides a way of informing others so that they can make informed decisions regarding the use of the treated water in shared aquatic ecosystems. Few applications are refused. Applicants will receive useful advice in the process, including any changes in approved chemicals and water use restrictions, safe methods for chemical application and requirements for posting signs.

2) Is there a fee for the DEQ permit?

There is no fee for a permit if the pond or lake is under single ownership. If ponds or lakes are owned by two or more households, the permit fee is based on the size of the treatment area. No fees are charged for treatment areas less than 1/2 acre. A $50 fee is charged for treatment areas of % acre to less than 2 acres. A $150 fee is charged for treatment areas of 2 or more acres.

3) When is the best time to apply aquatic herbicides?

Generally, late spring or early summer is the best time to apply herbicides. Plants are in a period of rapid growth and highly susceptible to herbicide treatment. However, always follow the label instructions for best results.

4) What chemicals are approved for use in Michigan ponds and lakes and what plants will they kill?

USE ONLY CHEMICALS SPECIFICALLY LABELED FOR AQUATIC USE! Algicides and herbicides approved for aquatic use and the plants they control are listed in Appendix 1. This listing should be used for preliminary planning only since chemical approvals for aquatic use may change. Up-to-date information should be obtained annually from your county MSU-Extension office or the DEQ during the permit application process.

5) How much algicide or herbicide should I add?

Dosage rates are listed on the label. FOLLOW LABEL DIRECTIONS CAREFULLY! General application rate recommendations cannot be made since chemicals may be sold with different levels of active ingredient or with different active forms. DO NOT OVER-TREAT! Over-treatment will increase the potential of killing fish and other aquatic organisms directly or indirectly by resulting in a rapid plant die-off and subsequent oxygen depletion due to decomposition. Some herbicides may not produce the desired effects if applied at concentrations above the recommended level. In general, treatment rates are based on acre feet of water of treatment area. Acre feet can be easily calculated by:

Acre feet = surface acres x average depth where:

Surface acres = Length (feet) x Width (feet) x 0.000023 or = Length (yards) x Width (yards) x 0.00021

6) Are there any limitations on pond use after herbicide application?

Use restrictions for lake and pond water after chemical treatment are listed in Appendix 2. This listing should be used for preliminary planning only because the listings may change. Up-to-date information should be obtained annually from your county MSU-Extension office or the DEQ during the permit application process. ALWAYS FOLLOW THE LABEL INSTRUCTION OR THE DIRECTIONS OBTAINED BY PERMIT.

7) Are algicides and aquatic herbicides safe to use?

Use directions on algicide and herbicide labels are designed to protect both the environment and the user from unreasonable risk. Maximum allowable dosage rates, proper handling and protective clothing (including goggles, face mask, coveralls, gloves and protective foot wear) will assure a high degree of safety. Once again, it is important to emphasize READ AND FOLLOW ALL THE LABEL INSTRUCTIONS CAREFULLY!

8) I've heard that a common aquatic herbicide 2,4-D causes cancer, contains dioxin and is hazardous to my family's health, is that true?.

A recent comprehensive review and evaluation of the safety of 2,4-D (Munro et al. 1992) was published in the Journal of the American College of Toxicology (Volume 1 1, Number 5). The reviewers concluded that the scientific evidence does NOT support the conclusion that 2,4-D causes cancer in humans. However, ALL LABEL RECOMMENDATIONS SHOULD BE FOLLOWED to ensure maximum safety.

2,4-D belongs to a family of compounds referred to as the phenoxy herbicides. Another member of this group of chemicals, 2,4,5,-T, has received considerable attention recently because it contains trace quantities of a particularly hazardous compound, 2,3,7,8 -TCDD, which is commonly referred to as dioxin. However, there are at least 75 different forms of dioxin compounds which are all much less toxic than 2,3,7,8,-TCDD. The technical grade of 2,4-D contains dioxins, including extremely low levels of 2,3,7,8,-TCDD; but the technical grade is considered safe by the EPA.

9) I've used Aquazine to control pondweeds for years but it is no longer sold, can I use other simazine products?

No. Only products labeled for control of pondweeds can be used legally in ponds. The manufacturer did not renew the aquatic label for simazine products when it expired because of concerns over possible groundwater contamination.

10) Are there any other precautions that I should take if I choose to use chemicals to kill my aquatic plants/algae?

• Yes. Regardless of the type of chemical used:
• DO NOT USE VERY OLD PESTICIDE PRODUCTS. Chemicals can change with time and become unsafe to use. Only buy the amount of chemical that you need.
• NEVER STORE PESTICIDES IN ANYTHING BUT THE LABELED CONTAINER. Pesticides are poisons which can cause serious illness or even death. Placing a pesticide in an unlabeled or mislabeled container could lead to a serious accident.
• DISPOSE OF OLD, UNUSED PESTICIDES AND EMPTY CONTAINERS SAFELY. Always follow label instructions. If instructions are not available, you can obtain information by calling your county MSU-Extension office, the Michigan Department of Agriculture (MDA), Pesticide and Plant Pest Management Division, or your regional MDA office.
• MDA Pesticide and Plant Pest Management Division P.O. Box 30017 Lansing, Ml 48909 phone: 517-373-1087 Additional information is available from your county MSU-Extension office: 'Hazardous Waste Disposal on the Farm,' MSU-Extension Bulletin E-1781 'Aquatic Pest Management: A Training Manual for Commercial Aplicators,' MSU -Extension Bulletin E- 2437.

11) If I decide to use chemicals to control nuisance aquatic plants, should I do this job myself?

• Many aquatic algicides and herbicides are labeled for use by the general public, while others are restricted to certified applicators only. IF YOU ARE UNCERTAIN ABOUT WHAT CHEMICALS TO USE, HOW TO CALCULATE TREATMENT RATES, AND HOW TO APPLY THEM, OR IF RESTRICTED CHEMICALS ARE NEEDED, HIRE A CERTIFIED AQUATIC PLANT CONTROL APPLICATOR.
• Current listings of certified aquatic plant applicators can be obtained from the MDA office listed above.

12) Do the blue dyes really help control nuisance aquatic plant growth?

The blue dyes may be used to reduce nuisance aquatic plant growth in very small lakes and ponds under certain conditions. The dye acts as a chemical shade by reflecting some of the blue wavelengths of light needed by the plants for photosynthesis. The plants cannot grow effectively without active photosynthesis. Dyes should only be added to very small lakes and ponds that are under the full control of the applicator. A permit from DEQ is required if conditions under question 1 are met. There are limitations to using dyes to reduce aquatic plant growth:

• Plants can still grow in the top 18 inches of water. If your pond has shallow bank slopes, large areas may be less than 18 inches deep and they will still support active plant growth. If the color intensity is not maintained, plants will grow. Ponds with flowing outlets will lose the die and the color intensity may decrease over time requiring additional dye treatments. Dyes must be retained in the treated water body, it is illegal to discharge the dye into a drainage ditch, stream, or lake.
• The dye may cause unwanted water colors if the water is not clear and should not be used in an attempt to change water color.
• Dye and herbicides or algicides should not be added to a pond at the same time. Plants must be actively growing for herbicides or algicides to be effective. After the herbicides and algicides have killed the nuisance aquatic plants, dyes can be added to reduce regrowth in the deeper areas of the pond. Dyes should not be used in ponds that are primarily used for swimming.

13) Can I selectively treat nuisance aquatic plants without eliminating desirable aquatic plants?

Nuisance aquatic plants may be selectively treated by using appropriate chemicals, using lower dose rates, or adjusting the timing of a chemical treatment. Approved granular forms of certain chemicals can be used to treat specific areas; however, drift of the chemicals from the area may occur making "spot" treatments less effective. Drift occurs as the result of wind and wave action after treatment or from inlake currents caused by springs or in- or out-flow from creeks and streams.

• As an example, the DEQ Inland Lakes Management Unit has been investigating the use of Sonar at low dose rates in Michigan lakes as a selective treatment of Eurasian watermilfoil. They are beginning to develop rules for Sonar use in Michigan. While the rules are being developed, DEO staff may begin issuing permits in regulated ponds and lakes (see question 1) to use Sonar under certain circumstances on a case by case basis, using site-specific information:

  1) Sonar at concentrations up to 5 ppb may be permitted in lakes with significant Eurasian watermilfoil infestations. The applicant must provide the following information with the permit application: documentation of significant Eurasian watermilfoil infestation; authorization from affected riparian property owners; accurate calculations of lake volume using depth contours; a comprehensive aquatic plant management plan that includes community input to the plan's development; and a Sonar concentration monitoring schedule.

  2) Sonar concentrations up to 8 ppb may be permitted in some regulated ponds with limited public trust value where environmental issues are minor (e.g., golf course ponds, stormwater retention basins, sewage lagoons, and commercial and subdivision ornamental ponds). The applicant will monitor and report Sonar concentrations.

  3) Sonar concentrations up to 8 ppb may be permitted in commercial marinas where adjacent wetlands and water bodies will not be affected. The applicant will monitor and report Sonar concentrations.

• Additional research is still needed to resolve several issues related to Sonar. The DEQ will complete follow-up vegetation surveys of lakes treated with Sonar in 1996. This will provide valuable information on vegetation response in post-treatment years.

14) Do I have any other choices in treating my aquatic plant problems?

Chemical treatment is only one of a number of band-aid treatments which remove the plants temporarily. Other types of band-aids include phosphorus precipitation chemicals, chemical or physical shading, harvesting, aeration, and water level manipulation. However, none of these band-aids cure the problem: excessive nutrients, primarily phosphorus. Phosphorus inputs must be limited by diverting nutrient laden runoff, use of fertilizers which contain no phosphorus, and the development of marshes and greenbeits (natural grass-shrub areas) to remove nutrients before they reach the lake or pond. Realistically, this may take years or may even be impossible as is the case in storm runoff storage ponds and lakes. Ponds and lakes may also have high levels of phosphorus in the lake basin which would reduce the effectiveness of limiting phosphorus inputs. Under these conditions, chemical treatment may be a desirable alternative to weed-choked or algal-filled lakes.

APPENDIX 1

IN ALL CASES, USE CHEMICALS SPECIFICALLY LABELED FOR AQUATIC USE AND FOLLOW THE WAITING RESTRICTIONS ON THE CHEMICAL CONTAINER! Never use chemicals from a container that lacks an up-to-date commercial label stating restrictions for aquatic use. The waiting periods below are a summary for chemical dosages on label instructions. DO NOT EXCEED DOSAGES IN THE LABEL INSTRUCTIONS.

by Donald L. Garling Department of Fisheries and Wildlife
Michigan State University
East Lansing, MI 48824

Links to other pond pages:

Mechanical Harvest of Nuisance Pond and Lake Weeds

Pond Construction
Pond and Lake Resources

Pond Permits

RESOURCES:

Handouts/booklets available from MSU Extension:

- "Managing Michigan Ponds for Sportfishing" describes construction, fish stocking, weed control.

MSU Extension, Genesee County: (810) 732-1470
NRCS (Natural Resource Conservation Service): (810) 766-5192
Soil Conservation District: (810) 230-8781
MDNR (Shiawassee District): (517) 625-4600
MDNR (Permits): (517) 373-9244
MDNR (Information): (517) 373-9400

Michigan State University Extension programs and materials are open to allwithout regard to race, color, national origin, gender, religion, age,disability, political beliefs, sexual orientation, marital status, or family status. MSUE-Genesee County is funded jointly by Michigan State University, the U.S. Department of Agriculture and the Genesee County Board of Commissioners. MSU is an affirmative-action equal opportunity institution.

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