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We haven’t touched upon the subject of “good weeds” of which there are many required by fish and wildlife. Perusal of the numerous websites showing pictures and descriptions of weeds -good and bad - will acquaint you with “what’s good”.
What are the remedies?? There are several common remedies:
- Hand pulling
- Harvesting
- Winter Draw Downs
- Hebicide treatments
- Dredging and
- Two uncommon remedies:
- Weed eating fish
- Insects, Weevils
Hand Pulling is a method to clear small areas and margins of lakes where heavy equipment cannot get access. An example might be machine harvesting of water chestnuts before they bloom and hand pulling those weeds in the shallow water and margins.
Harvesting makes use of machines made to operate in water and are equipped with mechanisms for cutting weeds below the surface. A typical harvester is shown below
The
left end contains the cutting mechanism and the hydraulic lifts for raising
and lowering the cutting depth. Behind the cutting mechanism is a traveling
grate for retrieving the cut weeds into the harvester.
To the right of the operator station is the traveling grate used to off-load the “harvested” load of weeds into a barge or on to the shore.
Harvesters do not kill weeds anymore than you kill your grass when you mow it. They merely open up channels by reducing the weed height in the water. Since harvester weed retrieval mechanism is not 100% effective, small cuttings float in the water and may sink to the bottom and re-root, thus spreading the weed infestation. They are very effective for temporary cosmetic fixes. Harvesters must be emptied periodically and great care must be taken in transporting the weeds to the dump site to avoid spilling fragments.
Harvester offloading a load of Water Chestnuts
Early harvesters were quite crude and undeveloped. They demonstrated that weeds could be cut underwater but the lack of weed retrieval caused propagation problems. Notice how simple this machine is.
Winter Draw downs of a water body are intended to be deep enough to expose the interstitial mud containing the targeted weed roots to freezing temperatures. Exposed long enough, the roots will heave and the plant will dessicate. In a perfect cycle the plant will dessicate and the heaving, thawing, and levitation of a rising water level will tear the plant roots from their berth. Draw downs have been effective, and ineffective depending on the co-operation of Mother Nature. Overall, draw downs are an effective tool in the battle against noxious weeds. However, they are not equally effective.
Lycott Environmental, Southbridge, MA, has an article on Draw Downs.
Synopsis
LAKE LEVEL DRAWDOWN AS A MANAGEMENT TOOL FOR AQUATIC
PLANTS
A PAPER BY LYCOTT ENVIRONMENTAL
Southbridge, MA.
Aquatic biologists and limnologists have used lake level drawdown or water level manipulation for many years to aid in the management of aquatic plants in water bodies. Most of the literature published on this management technique indicates that many aquatic plants can be reduced by desiccation and/or freezing.
While this natural phenomenon will help reduce aquatic plants in many water bodies, there are several items that need to be considered, and a number of conditions that must exist for effective management.
CONSIDERATIONS - Text covers 8 considerations: (1) Hydrology budget - how long to empty and refill; (2) Lake water outlet structure - does it allow lake level manipulation with flash boards, or valves, and spillways. (3) Bathymetry - are the contours of the lake bottom such that a drawdown of 3,4 or 5 feet would expose sediment and weeds that are targeted. (4) Private and Public Water Supplies - what effect will there be on shallow wells surrounding the lake when the lake level is lowered. (5) Ownership - Who owns the lake bottom, the outlet structure, are there downstream water rights. All are considerations for a drawdown. (6) Managment - Who manages the drawdown and makes decisions on weather impacts.(7) Gradient - Do yhe downsteam elevation profiles lend themselves to lake drainage at a reasonable rate.(8) Aquatic Plant Species - Are the plant species of the type that can be controlled with drawdowns.
METHODOLOGY - Discusses why management techniques must consider weather, timing, rate of drawdown and its effect on marine life, how long to maintain lowered level, and refill considerations.
CONCERNS - Several concerns are addressed: downstream impacts, Bordering vegetated wetlands, fisheries, and unsafe ice.
POTENTIAL NEGATIVE IMPACTS - covering loss of well water, recreational activity, aesthetics, effects on benthic organisms, doughnut effect, odors, disruption to moorings and docks, and floating weed islands
BENEFICIAL EFFECTS - lists the aquatic plants likely to be affected, phosphorous reduction, sediment scouring, Solar flexion and soil movement, sediment analysis, opportunities to abutters to improve beaches and exposed sediments, sediment consolidation and compression, depth and duration of frost levels.
PERMITTING - Who are the cognizant permitting authorities.
THE FULL ARTICLE IS AVAILABLE AT:
(Lycott Environmental is a long established professional organization
experienced in lake and watershed managment and limnology. Address: 600
Charlton St., Southbridge, MA 01550. Tel: 508 765 0101)
Herbicide Treatments, Dredging, Weed Eating Fish, and Insects (and other topics) for weed control are all covered in summary form by Chapter 5 of Roberta Goodwin’s Book on the University of Florida Web Site
Outline Synopsis of Chapter 5
Four principal methods: Physical removal, Habitat manipulation, Biological
Control, and Herbicides are discussed:
Physical Removal
- Hand Pulling
- Harvesting - with machines similar to previous photo
- Dredging - removal of muck and weeds from bottom
Habitat Manipulation
- Draw Downs (manipulation of water level) with a table showing sensitive plants (for southern waters)
- Light Penetration control - use of dyes
- Bottom (opaque) Covers such as Benthic Barriers
- Nutrient Limitation - such as watershed control, nutrient removal
Biological Control
- Insects
- Pathogens
- Grass Carp
Herbicides - sometimes known as Pesticides
Types
Contact - kill/injure on contact
Systemic - enter the plant system
Broad Spectrum (non selective)
Selective (attack only certain plants)
Toxicities levels of Herbicides - in concentrated form
Fate of Herbicides in the Environment - how they degrade
copper
2,4-D
Diquat
Endothal
Fluridone
Glyphosphate
