Managing Water Weeds (Aquatic Plants): Introduction

Table of Contents

1. Introduction
2. Integrated Weed Management for Water Weeds (Aquatic Plants)
3. Water Weeds (Aquatic Plants) Control Herbicide Rating Tables
   • Habitats and Herbicide Susceptibility of Common Aquatic Plants
     (Table 19-1) (PDF 80kb)
     Classification of Weeds According to Response to Various Foliage Sprays
     (Table 18-2) (PDF 62kb)
4. Herbicide Recommendations for Water Weeds
• Algae and Vascular Submergents
• Emergents
5. Related Links

Introduction

According to the Pesticides Act and Regulation 914 a person requires an Aquatic Vegetation exterminator's licence to use a herbicide to control aquatic plants ( water extermination) and a permit to purchase and apply a herbicide into water. There are some exemptions under Regulation 914 for a license and permit requirements as noted below.

Most, aquatic herbicides are classified into Schedule 2. Persons who hold an Aquatic Vegetation exterminator's licence may purchase a Schedule 2 herbicide for aquatic plant control without a permit. However, a permit is required by the holder of an Aquatic Vegetation licence to use aquatic herbicides on someone else's property.

A person who is the owner of a property, or his or her full time employee, upon which a water body is located does not require an Aquatic Vegetation licence to use a herbicide for aquatic plant control, if the water body is:

• Wholly contained within the boundaries of that property and that has no direct or indirect outflow, other than by percolation,

• A drainage ditch located wholly within the boundaries of his or her own property that at the time of the extermination contains no flowing water.

However, a person who is the owner of a property, or his or her full-time employee, requires a permit to purchase a Schedule 2 herbicide for aquatic plant control in that water body.

Note: Certified growers are permitted to purchase and use Schedule 2, 3, 4, 5 and 6 pesticides for a land extermination only on their own farmland. The use of an aquatic herbicide is a water extermination. Therefore, a permit is required by a Certified grower to purchase a Schedule 2 aquatic herbicide but not for its use.

Reducing or eliminating the flow of nutrients into water bodies is an effective preventative measure to control excessive aquatic weeds. Herbicides only provide temporary control of nuisance aquatic vegetation. Alternate methods such as mechanical removal of submergent plants, dredging or substrate alteration of drainage ditches can provide longer-term control. Mechanical control measures may have an impact on fish habitat and therefore would require approval from the Ministry of Natural Resources. Management techniques for vegetation control in ponds include minimizing nutrient input, dredging excess sediment, logs and other organic debris, decreasing the surface to depth ratio and increasing the rate of pond turnover (flushing). Some aquatic plant and algae life should be accepted and tolerated as a vital component of a healthy ecosystem.

Aquatic vegetation can vary widely; species include completely submerged plants such as Canada Waterweed and algae; free floating plants such as water lilies; and emergent plants such as cattails and bulrushes. Many emergent plants will grow equally as well on the moist shoreline as when their lower stems and roots are in water. Where these emergent species have taken possession of the shoreline, control measures must embrace that area as well as the water.

Stonewort and muskgrass are a gray green to green plant-like algae, attached to the sediment, or free floating. In dense communities this plant-like algae has a very strong musk odour. It is brittle to the touch and will dry to a white powder upon removal from the water.

Tapegrass (wild celery) is found in many recreational lakes, is resistant to all the currently recommended herbicides. It has long rubbery leaves and numerous short roots. Control is possible only by mechanical methods.

For further information on water extermination permits, contact the Ontario Ministry of the Environment Regional Office in your area. See Appendix D, Ontario Ministry of the Environment Pesticide Control Offices.

| Top of Page |

Integrated Weed Management for Water Weeds (Aquatic Plants)

Herbicides provide temporary control of nuisance aquatic vegetation. Alternate methods such as mechanical removal (Submergents), dredging or substrate alteration (drainage ditches) can provide longer term control. Management techniques for vegetation control in ponds include minimizing nutrient input, dredging excess sediment, logs and other organic debris, decreasing the surface to depth ratio and increasing the rate of pond turnover (flushing). Some aquatic plant and algae life should be accepted and tolerated as a vital component of a healthy ecosystem.

The use of herbicides may be complicated by the use of water by livestock or humans or by the presence of fish. If the water is flowing, the effect of the chemical on plant, animal, or fish life downstream must be considered. Flowing water, by diluting the herbicide, makes control less effective.

Emergent species such as cattails and bulrushes may have to be sprayed for 2 or 3 consecutive years to bring them under complete control. The chemicals for cattails and other emergents are sprayed so as to thoroughly wet all exposed foliage. Paraquat and amitrole are most effective when cattails are coming into head. Consult the manufacturer's directions.

The vegetation also varies widely; species include completely submerged ones such as Elodea (Elodea canadensis - Canada waterweed) and algae; free floating ones such as water lilies and emergent plants. Many emergents will grow equally as well on the moist shoreline as when their lower stems and roots are in water. Where these emergent species have taken possession of the shoreline, control measures must embrace that area as well as the water.

Chara (Chara stonewort, muskgrass) are a gray green to green plant-like algae, attached to the sediment, or free floating which in dense communities has a very strong musk odour. It is brittle to the touch and will dry to a white powder upon removal from the water. This plant is difficult to control with moderate doses of algaecides and dense communities should be removed mechanically. Tapegrass (wild celery) (Vallisneria americana); found in many recreational lakes, is resistant to all the currently recommended herbicides. It has long rubbery leaves and numerous short roots. Control is possible only by mechanical methods such as pulling.

Diquat (Reward) provides good control of a wide variety of submergent species including water-milfoil, pondweeds, Elodea canadensis (Canada waterweed) and Coontail. This herbicide is not effective against Chara spp. (Muskgrass) and Nitella sp. Diquat should be applied on cloudy days in late afternoon and care should be taken not to stir up the bottom since turbidity reduces the effectiveness of treatment. Since diquat takes effect rapidly, decomposition of a large plant mass may deplete oxygen levels which can cause fish to suffocate. Thus, in ponds where fish are present and growth is well established, no more than 1/4-1/2 of the pond should be treated at one time. Wait two weeks before treating again. The best time to apply these chemicals is late spring while the plants are growing rapidly. Since this is a contact chemical, control is achieved for one season, and repeat treatments must be made annually.

| Top of Page |

Related Links

• Weeds in Ontario
• Problem Weed Control in Field Crops
• Integrated Pest Management (IPM)
• Pesticide Application and Safety
• Pesticide Companies and Agents
• OMAFRA Sprayer Calibration Calculator
• Search the PMRA website
• OMAFRA Publication 505: Ontario Weeds
• OMAFRA Publication 75: Guide To Weed Control

   

  | Top of Page |