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Agriculture
Canada
Research Direction generate
Branch de la recherche
Technical Bulletin 1989-6F
aguculture CANADA
GOT 89/03/31 NO.
03
L IBRAF.Y/P inLIOTI -1ECJJE OTTAV A Kl A CT 5
Aquatic vegetation on the
Canadian prairies: physiology,
ecology, and management
630 . 72
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Canada1
Digitized by the Internet Archive
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http://archive.org/details/aquaticvegetatio19896alla
Aquatic vegetation on the
Canadian prairies: physiology,
ecology, and management
J.R. ALLAN, T.G. SOMMERFELDT, and J.A. BRAGLIN-MARSH
Research Station
Lethbridge, Alberta
Technical Bulletin 1989-6E
Lethbridge Research Station Contribution No. 14
Research Branch
Agriculture Canada
1989
t opies >>t (luv publication are available from
Di | K Ulan
soil Science Section
Research Station
Research Branch, Agriculture Canada
P.O Box 5000, Main
1 ethbridge, Mberta
1 IJ 4B1
Produced l>\ Research Program Service
C Ministei ol Suppl) and Services Canada 1989
Cat No \~>»-s I989-6E
lsB\ 0-662-16807-0
Cover illustration
The dots on the map represent
Agriculture Canada research
establishments.
CONTENTS
Page
SUMMARY i
INTRODUCTION 1
WATER IN THE LANDSCAPE 2
AQUATIC ECOSYSTEMS 5
Environment (abiotic or non-living component) 6
Biological community (biotic or living component) 8
AQUATIC PLANT CLASSIFICATION 10
Algae 10
Aquatic macrophytes 11
AQUATIC MACROPHYTE LIFE CYCLES 13
GOALS FOR MANAGEMENT PROCEDURES 15
Short-term management techniques 15
Long-term preventive management 16
AQUATIC VEGETATION MANAGEMENT TECHNIQUES 19
Non-chemical techniques 19
Habitat manipulation 19
Biological control 21
Chemical (herbicide) control 23
Algae 24
Submergent macrophytes 25
Floating-leaved macrophytes 26
Free-floating macrophytes 26
Emergent macrophytes 27
Marginal or ditchbank weeds 27
WATER QUALITY IN RELATIONSHIP TO AQUATIC PLANT GROWTH 28
APPENDIX I 31
SUMMARY
This publication describes the aquatic ecosystem and discusses the
interrelationships between the nonliving environment and the living
biotic communities. Emphasis is on the understanding of the life cycles
of aquatic plants and how their growth should be limited before it
becomes excessive.
Aquatic vegetation management techniques are discussed and control
procedures are given for specific aquatic vegetation problems in
different aquatic environments. This information should assist farmers,
irrigators, irrigation managers, water users and environmentalists in
understanding and planning integrated aquatic vegetation management
programs to preserve the Prairies' freshwater resources.
RESUME
Cette publication deer it l'ecosysteme aquatique. II y est egalement
question des relations reciproques entre le milieu abiotique et les
collectivites biotiques vivantes. On insiste surtout sur la comprehension
des cycles biologiques des plantes aquatiques et sur les moyens de
restreindre la croissance de ces plantes avant qu'elle ne devienne
excessive.
De plus, on traite des techniques de gestion de la vegetation aquatique
et on propose certaines mesures de controle a adopter pour regler des
problemes precis a ce chapitre dans divers milieux aquatiques. Grace
a ces renseignements, les agriculteurs, les irrigateurs, les exploitants
d'entreprises d' irrigation, les utilisateurs des ressources en eau et
les environnementalistes seront en mesure de mieux comprendre et de
planifier des programmes de gestion integree de la vegetation aquatique
en vue de preserver les ressources en eau douce des Prairies.
INTRODUCTION
The industrial and agricultural development along the East Slope of the
Rocky Mountains has created enormous demands for freshwater supplies and
these demands will increase in the years to come. Nearly one-half of
Canada's total irrigated land is in Alberta's 13 irrigation districts.
With new dams, improved on-stream storage, and more efficient delivery
systems, Alberta could double its 578,000 ha of land presently under
irrigation. However, aquatic vegetation can seriously impede the
movement of water through irrigation conveyance systems, reducing the
canal flow rates by as much as 91% of design carrying capacity. At
present, over 12,000 km of canals and drains in Alberta are plugged with
excessive aquatic weed growths. Some canals require as many as four
aquatic herbicide treatments per year to permit the irrigation districts
to meet peak water demands. Weed control costs in older main delivery
canals can reach $2,500/km per season.
This manual will outline the theories and goals of vegetation management
and the techniques available to control excessive aquatic vegetation in
agriculturally associated freshwater ecosystems. Information on the
composition of aquatic ecosystems is presented here to enable managers
to keep their system healthy, i.e., to maintain excellent water quality
while preventing excessive weed growth. A healthy freshwater ecosystem
permits the development of a management program that will generate
revenue from the system through aquaculture, the growth and harvesting
of aquatic organisms that can be marketed as food or food byproducts.
- 2 -
WATER IN THE LANDSCAPE
Water has always added to the aesthetic value and recreational potential
of land. The farm pond or dugout was originally built to supply water
for livestock and to irrigate the family garden. Later it was found it
could be used for domestic purposes excluding cooking and drinking.
Recently, the farm pond has begun to supply potable water after
filtration and water treatment. It also has a potential for boating,
fishing and swimming as well as being an attractor of wildfowl and wild
animals. When trees and shrubs were planted and a picnic table was
added for family outdoor meals, the pond became a place for relaxation
for the entire family as well as a source of water.
As leisure time increased, the public made greater demands for
water-based recreation. Urban parks have been developed along the
shores and banks of lakes and rivers. Abandoned gravel pits have been
converted into parks with biking and walking paths and man-made ponds
have been constructed to supply shallow ponds for leisure activities.
Golf course designers construct ponds to act as water hazards to
complement the sand traps and greens, which provide challenge as well as
aesthetic beauty for golfers and club members.
Urban land developers construct small lakes, 10 to 15 ha in size, as
focal points for new urban communities. The purpose of these man-made
lakes is to collect surface runoff to provide irrigation water for the
adjacent park areas and for the enjoyment and relaxation of the people
of the community.
As urban development continues, city planners are faced with increased
surface runoff problems from city streets and parking lots. This runoff
overloads the sewage treatment facilities. Storm water can not be
dumped directly into the river systems because it contains contaminates
such as silt and organic material washed in from the streets. The water
must be stored in storm-water retention or storage ponds to allow the
silt and other material to settle and then it can be released slowly
into natural drainage systems. While these ponds do not contain water
of top quality, they can be used as focal points in city parks and green
strips .
Even agricultural irrigation reservoirs, on-stream storage ponds,
irrigation canals and drainage canals developed for the production of
food are subjected to public pressure for further development into
recreational areas. Canal banks and shorelines are excellent habitats
for waterfowl and wildlife and large reservoirs offer recreational as
well as commercial fishing possibilities.
The vast diversity of these aquatic environments is evident; a great
variety of physical, chemical and biological characteristics exist in
each system. However, they all have one thing in common: they are all
highly eutrophic, meaning that they are nutrient-rich.
- 3 -
Eutrophic bodies of water are characterized by a shallow to intermediate
depth, variable surface area, and oxygen levels that decrease sharply in
the summer. They are subjected to nutrient enrichment from surface
runoff and water temperature that rises rapidly in the summer, and they
contain an abundance of dissolved nutrients and sediments that wash in
from the surrounding land. These factors contribute to an overabundance
of aquatic vegetation.
The seasonal growth and decay of this vegetation has a compounding
effect on the aquatic ecosystem. The excessive growth of rooted aquatic
macrophytes causes stagnation of the water column. This stagnant water
generally has a higher temperature than that of flowing water.
Increased water temperatures stimulate the growth of algae, both
filamentous and planktonic, which in turn increases the organic content
of the ecosystem. This creates a greater demand for dissolved oxygen.
With the continued demand, the levels of dissolved oxygen drop and fish
and related organisms are killed, which adds more organic matter and
stagnation to the ecosystem. Bacteria begin to work on the decaying
organic matter, odors are released into the water, the aquatic
environment deteriorates further, and the aesthetic quality is
destroyed.
For maximum fish growth and reproduction there must be at least 50% open
water (research data from the United States suggest as high as 60% open,
weed-free water for maximum sunf ish and perch production) . This allows
for a normal size gradient from fry up to mature adult fish. The open
water is the area for the adults while the fry seek refuge in aquatic
vegetation in the shallower areas.
Trout require a minimum dissolved oxygen content of 3.0 ppm; serious
die-off occurs at levels below 2.0 ppm. Widely fluctuating oxygen
levels tend to shift the fish population from game fish to the coarse
fish. As the water column warms in the summer, the ability of the water
to retain oxygen decreases and the heavy phytoplankton blooms appear.
When these blooms die, the biological oxygen demand increases and as the
oxygen levels in the water decrease, even the coarse fish die off.
As the water body deteriorates, the nutrients and organic matter
continue to increase and the aquatic vegetation becomes even more
abundant. When the vegetation reaches the surface of the water, it
forms mats which raise the surface water temperature. This increases
water loss through increased evapotranspiration from the water's
surface. Once this aquatic vegetation starts its prolific growth, it
continues to increase in density, causing further deterioration in water
quality and a subsequent large buildup of organic matter, which drops to
the lake bed and contributes nutrients for further weed growth.
In a very short time, usually three to five years, a water body can lose
its aesthetic value, the fishery can be destroyed, the water quality
- 4 -
deteriorates, odors develop from the rotting vegetation, and where the
water is used for irrigation the aquatic vegetation and debris begin to
plug intake screens and pumps. Dense vegetative growth will also block
turn-outs, thus preventing the movement of water from the water body.
The goal in aquatic vegetation management must be to prevent the buildup
of excessive vegetation. Corrective steps after the buildup occurs are
very expensive and, in the case of aquatic herbicides, the treatments
must be applied year after year. To develop a successful aquatic
vegetation management program we must first understand the aquatic
ecosystem: what makes up the total ecosystem; where the water and
nutrients come from; how the different components interact with each
other, and, finally, how a semblance of balance can be maintained to
keep the aquatic ecosystem healthy, viable, and functional.
- 5 -
AQUATIC ECOSYSTEMS
Aquatic ecosystems are dynamic systems which are in a state of slow but
continual change both physically and biologically. Like most biological
organisms, they undergo a constant aging process. Natural freshwater
lakes can be viewed as small worlds composed of environmental factors
and living organisms organized and bound together by interdependences of
food and interrelationships of energy. These lakes may be influenced by
surface runoff from the surrounding land and by the people who use and
manage this land. Human activities may accelerate the natural aging
process through increased and enriched surface runoff and the lake thus
may become highly eutrophic over a shortened period of time. Young
aquatic ecosystems begin nutrient-poor, with a low organic matter
content that restricts the biological component of plants and fish.
This is called an oligotrophic water body. As the water body matures,
it receives more nutrients and silt from surface runoff, the organic
content of the water increases and the aquatic vegetation becomes more
abundant. This vegetation offers food and shelter to numerous aquatic
organisms. This in turn begins to support a small game fish
population. The body of water is now called mesotrophic.
When the water body reaches middle age it has received years of fertile
runoff and is very nutrient-rich with a high organic matter content in
the water column as well as the sediments. The aquatic vegetation is
overabundant and there is very little open water. This overproduction
of organic matter causes the oxygen levels to fluctuate widely and the
fishery to shift to a few coarse fish. If organic matter production is
allowed to continue, the water body will in time fill in with organic
matter and become a marsh and then a swamp or muskeg. This is the
natural aging process for a freshwater ecosystem.
Agriculturally associated freshwater ecosystems are usually aquatic
systems that are made or at least modified by man. They may be small
lakes, reservoirs, ponds, or dugouts that contain standing water; they
are lentic environments. If the water is moving, such as in rivers,
streams, creeks, irrigation delivery canals, farmer supply canals and
drainage canals, the water system is referred to as a lotic
environment. This distinction is important since we will see later
that the type of aquatic vegetation and the preventive and corrective
vegetation management techniques applied will depend on the type of
aquatic environment involved.
These aquatic environments are only a small part of the total farm or
irrigation district. They are composed of the physical environment,
namely the water, the sediment of the pond bed, shorelines or banks, and
the living organisms or biological community. The surrounding or
adjacent land that supplies the surface runoff is the watershed and
development on this watershed comprises the urban or rural land use
pattern. The water may come from the local watershed or it may
- 6 -
originate from an outside source such as irrigation water. It may stay
on the site or pass through the site. The quality of the water is
dependent on the quality of the input as well as the quality of the
water that is discharged. The critical point to remember is that the
better the water quality the fewer the aquatic vegetation problems/ and
hence less erosion and flooding, lower maintenance costs, fewer problems
with irrigation equipment, fewer water taste and odor problems and
greater aesthetic benefits to the landowner and the general public.
Large natural lakes with their large volume of water are essentially
self-sustaining and require only radiant energy, the non-living or
abiotic environment, and the communities of living or biotic organisms
to function. These organisms act in the roles of producers, consumers,
and decomposers to make the ecosystem function. Generally, the large
system is very stable and essentially self-sustaining, being maintained
more or less independently of the influence of other outside
communities. The smaller agriculturally associated ecosystems, however,
are much less stable and require outside help to maintain their
equilibrium. Because change will manifest itself very rapidly, the
system must be monitored closely. This should be viewed as a positive
point since it means that we can manipulate the agricultural ecosystems
to prevent excesses or correct deficiences. It only requires that the
manager spend as much time on the aquatic ecosystem as on the rest of
the agricultural holdings.
Environment (abiotic or non-living component)
The environment or non-living component of the aquatic ecosystem is
composed of the sediments and soil of the banks and shores of the water
body, and the water. The water is the most visible and important of the
three. Of the many extraordinary properties of freshwater that
contribute to its ability to maintain life in aquatic ecosystems, none
is more important than the capacity of water to hold substances in
solution and its ability to enter into numerous chemical reactions.
Many of the naturally occurring elements of the earth's crust can be
found in inland fresh water. Some of these substances occur in minute
concentrations but in most cases they are only needed in minute
quantities to support aquatic life.
Of all the chemical substances in fresh water, oxygen is one of the most
significant both as a regulator of metabolic activity in the communities
and the individual organisms and as an indicator of the health of the
aquatic ecosystems. This oxygen exists as a dissolved gas in the water
and may be derived from atmospheric oxygen or from the photosynthetic
activity of green plants. The oxygen moves through the water column and
may enter the sediments where it takes part in the oxidation of various
compounds. The extent to which a compound may undergo oxidation-
reduction processes is dependent on the concentration of other oxidizing-
reducing systems and their products in the sediments and water column.
- 7 -
This oxidation-reduction potential or redox potential is important to
the cycling of the nutrients such as phosphates from the sediments and
their subsequent availability for the excessive growth of aquatic
vegetation.
The other major dissolved gas in the aquatic ecosystem is carbon
dioxide. This gas contributes three essential factors to the water.
First, it acts as a buffer in the water to protect against rapid shifts
in the acidity-alkalinity state. Through its reaction with water,
carbon dioxide may form a weak acid, neutral salts, or a weak base in
the water column. The maintenance of the near-neutral conditions in
mineralized fresh water is due to the carbon dioxide-bicarbonate-
carbonate complex. The second contribution is the role of carbon
dioxide in regulating biological processes such as seed germination and
plant growth as well as being involved in animal respiration and oxygen
transport in blood. The third and most important contribution is that
carbon dioxide is a source of carbon, one of the most versatile of all
the elements in the aquatic ecosystem. Carbon dioxide and water supply
the major components of carbon, oxygen, and hydrogen necessary for all
living organisms.
The most conspicuous dissolved compounds found in varying concentrations
in fresh water are the major anionic compounds such as carbonates,
sulfates, phosphates, and nitrates and the minor anionic compounds of
chlorides, sulfites, silicates, and nitrites. These compounds occur in
combination with the major cationic elements of calcium, sodium,
potassium, magnesium, and iron to form ionizable salts. Occurring at
much lower concentrations are the minor or trace cationic elements of
cobalt, zinc, copper, manganese, molybdenum, and boron. Generally, both
the qualitative and quantitative composition of the fresh water are
influenced by the geochemistry of the watershed surrounding the basin
through which the surface runoff flows to reach the water body.
The inorganic composition of the water body is further modified by
precipitation and concentration of salts due to evaporation. The total
concentration of dissolved compounds or minerals is a useful parameter
for describing the suitability of the water for irrigation, livestock or
domestic use. This measure, total dissolved solids, is the dried
residue of the water containing both inorganic and organic materials.
The quality and quantity of the dissolved solids in large part determine
the type and abundance of aquatic vegetation found in the ecosystem.
The sediments of aquatic ecosystems differ from terrestrial soils in a
number of fundamental ways, thus providing a unique environment in which
the aquatic plants take root and derive much of their nutrients.
Sediments are typically anaerobic except for a few centimeters at the
interface of the water column with the sediment bed. The inorganic
compounds are primarily in the reduced state. At the interface with the
water column the inorganic and organic compounds may undergo oxidation
and diffuse up into the water column. Generally, there is a rich
- 8 -
organic layer of particulate matter of decaying vegetation from 25-30 cm
thick that floats over the sediment. Numerous adaptations are required
by the submerged rooted aquatic macrophytes and their root systems to
exist on this unique substrate and function under these physiological
stresses. The aquatic plants exert a pronounced effect on the physical
and chemical properties of the bottom sediments. Once submerged plants
are established, their vegetative tops stimulate the settling of
additional sediments by decreasing the water flow velocity and creating
underwater currents.
Although extensive literature is available on the role of the
rhizosphere of agronomically important terrestrial plants, little is
known about aquatic plants. It is safe to suggest that the microfloral
rhizosphere of aquatic plants probably plays a critical role in the
nutrient uptake and subsequent vegetative growth of aquatic plants.
More research into the interactions between the aquatic plant root
systems, the sediments, the availability and uptake of nutrients, and
the microfloral rhizosphere will give us a better understanding of the
nutritional physiology of aquatic plants. This will lead to the
development of innovative, ecologically safe vegetation management
techniques to prevent excessive plant infestations and to even encourage
beneficial aquatic vegetation.
Biological community (biotic or living component)
All agriculturally associated aquatic ecosystems are composed of
biological communities of plants, animals, bacteria, and fungi. The
maintenance of these communities is dependent to a great extent upon
food relationships and energy flows that involve interactions between
the non-living environment and the biological communities. In a small
system these relationships are so closely connected that a change in one
nutrient can cause a serious disruption in the entire ecosystem. The
basic operation of the community's metabolism rests on the roles that
the different organisms perform at various nutritional levels in
maintaining the transfer of energy in the form of food through the
various individuals of the aquatic ecosystem.
The aquatic vegetation makes up the group referred to as the primary
producers. These organisms use nutrients from the water and sediments,
dissolved carbon dioxide from the water, and solar energy to produce
energy-containing organic substances through photosynthesis with the
oxygen released back into the water. The organic substances are used by
the plants to grow and reproduce. The consumers, mainly animals, are
incapable of synthesis of matter from the sun's energy and hence depend
directly on the producers. Within this group we recognize the
herbivores, which feed on aquatic vegetation, and the carnivores, which
feed upon herbivores or other carnivores. Both subgroups use the
dissolved oxygen given off by the green plants to grow and develop while
returning carbon dioxide and energy from respiration to the water
- 9 -
column. The decomposers are composed of heterotrophic bacteria and
fungi which in turn break down the organic substances from both the
producers and consumers and return the inorganic and organic nutrients
to the water column to be recycled by the producers.
The various links in the food chain represent different levels of food
synthesis/ feeding and being fed upon, and nutrient release by decay.
The aquatic ecosystem is thus a pyramid with the dissolved nutrients at
the base. The algae and aquatic macrophytes or producers occupy the
next level. Located on and in the sediments of the water body are the
bacteria and fungi of the decomposer group that break down the organic
matter. The next level is composed of the grazing herbivores followed
by the small carnivores such as trout fry. Last are the medium and
large carnivores such as the perch, trout, and finally the pike of the
consumer group.
While our major concern is the management of aquatic vegetation of the
agriculturally associated aquatic ecosystem, it can readily be seen that
the entire ecosystem is interrelated and what we do to one small segment
may have a pronounced effect on the entire system.
- 10 -
AQUATIC PLANT CLASSIFICATION
The aquatic vegetation, or primary producers, is composed of two major
groups of plants: the microphytes or algae and the macrophytes or
vascular plants. Before any vegetation management program can be
developed for our agriculturally associated aquatic ecosystems, the
water bodies must be surveyed and the specific problem areas examined.
After surveying, the nuisance aquatic vegetation must be properly
identified.
Algae
Algae are plants of simple structure and organization and lack true
leaves or flowers. They reproduce asexually by continuous vegetative
growth and from specialized cells or minute spores. Generally
free-floating, a few specialized species may become attached to
submerged rocks, grow on damp soil, or even grow on the ice face of
glaciers. Algae vary in size from microscopic forms to giant seaweeds
that extend several hundred feet in the oceans. They are found in
oceans, lakes, ponds, swamps, rivers, creeks, and canals where they can
grow down to the depth of light penetration. Algae are considered
primitive because the individual plant cell is capable of carrying out
all the critical life processes without the assistance of specialized
cells or tissues found in higher plants.
The algae found in our agricultural water systems are subdivided into
three subgroups:
1. phytoplanktonic algae
2. filamentous algae
3. branching algae
The phytoplanktonic algae are microscopic, free-floating, only
slightly mobile and exist at or near neutral buoyancy, usually existing
in the upper 1 to 2 meters of the water column where they are subjected
to the surface movements of water currents and wind. Phytoplankton
production is influenced by sunlight, water temperature, dissolved
inorganic and organic nutrient content of the surface water, the size,
shape, slope and type of pond bed, and water currents. Phytoplankton
are best known for the production of summer water blooms which cause
colored water because of the rapid proliferation of algal colonies. In
agricultural water systems the green water usually comes from species of
Anacystis, Microcystis, and Anabaena; blue to blue-green water from
Aphanizomenon; and reddish-brown water from Oscillatoria, Melosira,
Fraqilaria, and Navicula. Generally, phytoplankton do not interfere
with irrigation systems but may cause serious problems in ponds and
dugouts where toxic algae can kill hogs, sheep, and cattle. These
plants decrease the aesthetic quality of the water, may cause
objectionable odors and tastes, and in isolated incidences may cause
- 11 -
summer fish kills because the collapse of the massive blooms causes
serious oxygen deficiencies or releases toxins into the water column.
During the collapse and death of individual phytoplankton blooms,
bacterial populations may build up because of the breakdown of the algal
cells and the release of organic matter into the water. This can cause
additional nutrient enrichment, odors, and objectionable taste problems.
The filamentous algae are colonial types that consist of long,
stringy, hair-like strands of cells. They may be attached to the pond
bottom, draped over rooted macrophytes, or form floating mats or 'scums'
on the surface of the water. The filaments may be bright green to
yellow-green in color and appear as cotton-like masses on the surface of
the water (Cladophora) ; be dark green in color and feel like coarse
horse-hair (Pithophora) ; or appear as loose, slimy strands, bright green
and rising from the pond bottom (Spirogyra) . The filaments may form
large mats that can clog screens, intakes, pumps, and sprinkler heads of
irrigation systems. During hot, sunny weather the algae may trap air
bubbles in the filaments and float up to the surface where it forms
extensive mats that interfere with water-based recreation. These
surface mats also increase the adsorption of radiant energy from the
sun, causing the water temperature to rise. This in turn increases the
evapotranspiration of water. During periods of drought this water loss
can be critical to farmers and ranchers.
Branching algae are the most advanced algae possessing stems and
branches. They grow attached to the pond bottom but lack true roots.
They are usually found in hard water and have a gritty feeling when
crushed because of the high calcium deposits in their vegetative parts.
They are low-growing and generally cause very little trouble to the
farmer or rancher. The low-growing, creeping habit makes it an
excellent plant to stabilize and hold down the silt of pond or dugout
bottoms. Branching algae are excellent cover for small aquatic
organisms such as freshwater shrimp, which serve as food for fish.
Chara and Nitella are the only representatives found in Canada and may
be mistaken on first glance for coontail or water milfoil. The key
difference is that the algae lack true roots and do not have true flower
heads. When crushed, Chara will give off a strong musky, fish smell.
Aquatic macrophytes
The aquatic macrophytes or vascular hydrophytes are classified very
simply according to their habit of vegetative growth:
1. submergent macrophytes
2. floating-leaved macrophytes
3. free-floating macrophytes
4. emergent macrophytes
5. marginal or ditchbank macrophytes
- 12 -
Subroergent macrophytes grow completely submerged at water depths from
0.5 to 5 meters and are rooted in the hydrosoil. Although the plants
are totally submerged, the flower heads may extend to the surface of the
water and above for wind or insect pollination. The leaves may be
thread-like, ribbon-like, broad or finely dissected. Four distinct
types of leaf attachment occur in the submerged macrophytes. Whorled
leaf arrangements have more than two leaves attached at the same point
on the main stem (Ceratophyllum demersum, Myriophyllum spp., and Elodea
canadensis) . Opposite leaves are those with just two leaves attached at
one point on the main stem but the leaves are attached opposite each
other ( Zannichellia pulustris and Najas f lexilis) . The alternate leaf
attachment is where a single leaf is attached to each point along the
main stem (Potomageton crispus, P. praelongus, P. richardsonii, P.
gramineus, P. f iliformis, P. pectinatus, P. vaginatus, P. zosterformis,
P. pusullus, P. f riesii, P. berchtoldii, P. foilose, and Ruppia
occidentalis) .
The floating-leaved macrophytes grow on submerged soils at water
depths of 0.25 to 3.5 meters. In crowded habitats, the large leaves
float to the waters surface on long flexible petioles. This subgroup is
represented by the waterlilies (Nymphaeo and Nuphar spp.) as well as a
few dimorphic pondweeds (Potomageton natans, P. gramineus and P.
vaseyi) .
Free-floating macrophytes are typically unattached plants that float
freely on or just below the surface of the water. Some species may have
extensive root systems extending down into the water column. In Canada,
they range from the subsurface floaters with no roots (Utricularia spp.
and Lemna trisulcata) to the surface floaters with very simple roots
(Lemna and Spirodela spp.).
Emergent macrophytes are rooted in waterlogged soils, soils covered by
up to 0.5 meters of water, or on exposed mud flats above the waterline
but where the water table is within 0.25 meters of the soil surface.
The plants are mainly perennials growing from creeping rhizomes or
rootstocks. The mature leaves and stems as well as the flower parts are
aerial. This subgroup is represented by Typha, Scirpus, Juncus, and
Carex spp., Phragmites maximus, Zizamia aquatica, and Flumen festuccea.
The marginal or ditchbank plants are really terrestrial plants
commonly found along waterways, ditchbanks, and in moist, seepage waste
areas. These include many of the grasses (Gramineae spp.) such as manna
grass, wild millet, cut-grass, blue joint grass, and reed canary
(Glyceria spp., Echinochloa spp., Leersia oryzoides, Calamagrostis spp.,
and Phalaris arundinacea) . Also in this subgroup are the woody
herbaceous shrubs and trees of Cottonwood, willows, wild rose, and water
hemlock (Populus spp., Salix spp., Rosa acicularis and Cicuta spp.).
- 13
AQUATIC MACROPHYTE LIFE CYCLES
After identification of the aquatic weeds, the complete life cycle of
each group of aquatic macrophytes must be determined, from the breaking
of dormancy of the seed or tuber to the early development of the
seedling to the initiation of flowering and the subsequent development
of the seed, overwintering turion or winter bud. The rate of vegetative
growth is important since chemical control measures are usually most
effective and economical during a brief time of early plant growth or
just after the initiation of flowering. Late in the season the mature
plants are usually more resistant to the herbicide because of a heavy
layer of marl (calcium carbonate) encasing the leaves, which prevents
the absorption of the herbicide. Also, the total plant biomass may be
so great that the dosage necessary to build up a toxic level of
herbicide in the aquatic plant tissue makes the application of the
herbicide uneconomical, environmentally impractical, and perhaps even
unsafe. It is imperative that the mode of reproduction in the different
aquatic plant species be fully understood.
The aquatic macrophytes in western Canada increase and become serious
weed problems through prolific asexual or vegetative reproduction.
After the first introduction, over 90% of the subsequent reproduction is
by vegetative means. A cut or broken stem tip, 2.5-5.0 cm long and
containing two whorls of leaves, can produce roots in 3-5 days, become
attached to the substrate in 5-7 days, and will produce a water milfoil
plant in 4 weeks. Canada waterweed and coontail can also reproduce by
this fragmentation method and spread quickly throughout the aquatic
ecosystem in two growing seasons.
Where overwintering buds, dormant apices, and specialized overwintering
turions are formed at the ends of the vegetative shoots, the use of
mechanical harvesters actually spreads the aquatic plant infestations
and increases the density of the plant populations. The cutting of some
rooted submerged aquatic plants by mechanical means tends to make the
plants bushier and, as the plant matures, there are many more vegetative
stem tips which give rise to overwintering structures. These drop to
the mud of the pond or canal bottom and remain dormant until the
following spring when they begin to grow as the water warms up. The
tuber-producing pondweeds can also be stimulated to produce large
numbers of axillary tubers and stoloniferous runners when subjected to
cutting.
The pondweeds, particularly P. pectinatus, are known for their prolific
production of tubers when given sufficient nutrients and space, with
ideal physical and chemical conditions of the substrate. One tuber of
P. pectinatus planted in a child's wading pool in April and given ample
light, nutrients, warm water, and a rich organic mud for a substrate can
produce up to 36,000 subterranean tubers, 6,000 seeds, and 1,000
axillary tubers in a single growing season.
- 14 -
Once established in a reservoir or canal, the plant begins a prolific
vegetative reproduction by runners, dormant apices, tubers, turions or
seeds and rapidly develops a dense stand which slows up the flow of
water and causes a further deposition of silt and organic matter, which
further stimulates aguatic plant growth.
Geotextiles and geomembranes (such as polyethylene, polyvinyl and butyl
rubbers) used to line ponds and canals are often held in place and
protected from the sun by a 5-25 cm layer of soil on top of the liner.
The soil provides a good seedbed for shallow-rooted pondweeds such as P.
pusillus to become established and to spread by runners and small
vegetative dormant apices. A layer of soil, 2.5-5.0 cm thick, above the
herbicide-treated canal bottom is enough to permit the shallow-rooted
aquatic weeds to become established. However, the herbicide in treated
soil below this deposition is still effective for the control of
deep-rooted aquatic species.
It should be evident that control and management techniques must be
matched to the problem plant species and their mode of vegetative growth
and reproduction. From the general life cycles of the four different
groups of aquatic plants one can determine the most susceptible times
within the life cycle of the plant and select control procedures that
are most effective to control the problem infestation with the least
impact on water quality and the environment.
- 15 -
GOALS FOR MANAGEMENT PROCEDURES
Short-term management techniques
Until a long-term management program can be developed to manage the
varied aquatic ecosystems, temporary or cosmetic corrective measures of
integrated mechanical and chemical techniques will have to be used.
Although critics may complain of the pollution and destruction of our
environment through the use of aquatic herbicides, it is just as
criminal to sit back and do nothing. Aquatic plants have a tremendous
capacity to reproduce and to spread once introduced into an aquatic
environment, and to eventually destroy the aquatic ecosystem through
stagnation of the water, the subsequent deposition of mineral sediments,
and the production of large amounts of organic matter from the decaying
plant matter. This organic matter decomposition depletes the water
column of oxygen and causes deficiencies, particularly during the winter
months when the water is ice-covered. Odor and taste problems may
develop as well as destruction of the fish population from lack of
oxygen. Stagnation also causes reduced circulation of the water and
subsequent stratification of the water column. The aquatic ecosystem is
in a constant state of change. Today's technology helps maintain and in
some cases improve the water quality of our freshwater ecosystems when
they become stressed through overuse and abuse. Many management
techniques can, in reality, restore the ecosystem to its normal sequence
and rate of change.
Many different aquatic plant harvesting machines have been developed
since the mid 1940s. Basically, the harvesters have been designed as 1)
underwater cutters which cut the weeds and an inclined porous conveyor
which collects the cut material and loads it into a holding compartment;
2) a transporter system to move the cut material from the cutter holding
compartment to the shore; and 3) an unloading facility on shore to move
the material from the transporter to trucks for delivery to a disposal
site. Recent modifications have included equipment to dewater, shred
and compact the bulky plant material to make transportation and disposal
more economical. The big advantage of cutting and harvesting the
aquatic plant material is the removal of the plant nutrients and organic
matter from the water column and the aquatic environment.
The main disadvantages are the fact that the plants start regrowth
immediately after cutting and develop a bushier habit of growth and
stimulate greater development of asexual reproductive structures. Dense
aquatic weed populations slow the forward cutting speed of the
harvester, because of the resistance of the matted cut material on the
pick-up conveyor belt. Speeds exceeding 1 km/hr cause a large
displacement of water in front of the cutter/conveyor and the cut plant
material tends to move around the pick-up system. Any plant material
that escapes the pick-up system acts as a source of new aquatic plant
infestations. The increased bulk of plant material, which is about 85%
- 16 -
water, increases the problems of transportation and disposal since the
material must be drained of water and then dried down for final
disposal. Mechanical cutting tends to be very capital- and
labor-intensive and is a slow, tedious process. One must weigh the cost
and slowness of the cutting operation along with the potential for
developing bushier aquatic plants and spreading of aquatic plant
infestations throughout the ecosystem against the advantage of removing
the organic matter from the ecosystem, the removal of some of the
nutrients bound up in the plant material, and the fact that no new
foreign substances are added to the freshwater ecosystem. The
environmentally acceptable mechanical cutting method may, in fact, cause
the spread of the problem and do more harm than the spot treatment with
a small amount of aquatic herbicide.
Aquatic herbicides are easy to apply and require a minimal amount of
capital expense and labor. Since they are so easy to apply, a
misconception may be that if there is nothing else to do, then go out in
the boat and "treat the weeds". However, aquatic herbicides are just
like medicine; you must prescribe the correct herbicide at the
prescribed dosage for the specific problem aquatic plant at its most
susceptible growth stage. Applied too late in the season or at too low
a dosage, the herbicide may just chemically prune the target aquatic
plants. If a herbicide is applied too often, the plant may develop a
resistance to it or, worse still, the herbicide may select out resistant
aquatic plant species that can take over the ecosystem. Treating an
aquatic plant biomass that is too extensive will create serious problems
when the plant material drops to the pond bottom and causes an organic
matter buildup. A problem of real concern is the use of aquatic
herbicides to treat only the visible result of a deeper, more basic
problem, causing the excessive growth of specific plant species in the
freshwater ecosystem. Once started, the aquatic herbicide program must
be planned as a yearly maintenance procedure to selectively control
excess vegetation, to minimize interference with water use, and to apply
the herbicide at the correct time to attain maximium effectiveness.
In old, mature ecosystems the best program would be an integrated
program using mechanical and chemical management techniques. Here the
overabundance of aquatic vegetation is cut to remove it from the lake or
pond. This removes some of the nutrients and a fair amount of the
organic matter. Then herbicides could be applied at a reduced dosage to
kill the remaining plants and to prevent regrowth and reinfestation due
to fragmentation and clippings.
Long-term preventive management
Most bodies of freshwater will become infested with aquatic vegetation
in time. Aquatic plants are necessary for the stabilization of the
sediments, the oxygenation of the water column, and the shelter and
protection of aquatic organisms. Seeds and tubers of aquatic
- 17 -
macrophytes are important sources of food for waterfowl and wildlife.
Aquatic ecosystems should be designed and managed to control excessive
aquatic plant growth through the manipulation of the water body and the
surrounding watershed. Aquatic plants do not grow well on rocky,
gravelly or clay pond or canal beds. They prefer an organic-rich
substrate with a steady supply of nitrogen and phosphorus. They grow
very slowly at water temperatures below 15°C and cannot tolerate
shading. With this knowledge, guidelines can be set for the design of
ponds, reservoirs and irrigation conveyance systems to minimize
potential aquatic weed problems.
The bottoms of ponds and canals should be excavated down to clay to
prevent seepage and to provide a harsh environment for the introduction
and development of aquatic seedlings. If the pond or canal site
contains a high percentage of coarse-grained soils, then the bottom
should be lined by 'blanketing' with a 30-cm layer of packed clay. If
clay is not available at the site then the pond or canal should be lined
with geotextiles. Slopes and canal banks should be lined with rocks and
gravel to prevent erosion. If geomembranes or geotextiles are used for
lining the pond or canal, then the covering material should be coarse
and nutrient-poor. Once a harsh environment is established in the pond
or canal it is imperative that the silt content of the introduced water
be controlled through the use of silt traps and sediment catch basins.
Little is accomplished if the rocky bed is allowed to silt in, because
just 2.5-5.0 cm of sediment is enough for shallow-rooted aquatics to
become established. This is particularly important during
rehabilitation work because all the improvements are for nothing if part
of the system can still release sediments and nutrients into the newly
renovated pond or canal. Canals in southern Alberta can deposit enough
sediment at bends in the canal in one season to permit the deposition of
sediment-rich substrates for colonization by P. pusillus . After the
pondweeds become established, the sediment deposition extends further
upstream and increases in depth. Soon the deeper-rooted pondweeds such
as P. pectinatus and P. richardsonii begin to appear in the center of
the siltbar. Once established, the pondweeds extend into the harsher
areas between the rocks and coarse gravel and continue to spread.
Within five years the rehabilitated canal can be so infested that the
delivery capacities are seriously reduced because of restricted flow.
The weed bed can now serve as a source of plant inoculum for the rest of
the canal system downstream.
The surrounding area must be landscaped and managed to prevent the
introduction of nutrients from soil and organic matter carried into the
pond by surface runoff and wind erosion. In the western Prairies the
wind can be a problem and every effort should be made to establish
windbreaks and shelter belts to prevent soil drifting into the ponds,
dugouts, and canals and to retain snow for spring runoff. Shelter belts
must be placed far enough away from the pond, reservoir, and canal bank
to allow for a grass vegetative filter area to intercept sediment in the
spring runoff. This will prevent the direct introduction of organic
- 18 -
matter into the water. The area must be fenced to keep livestock away
from the water's edge, thus preventing the destruction of the banks and
the introduction of nutrients from manure. Particular attention should
be paid to runoff gulleys and field drainage areas to prevent flash
flooding and soil erosion.
Lastly, "dilution is never the solution"! Waste water must be treated
to prevent the introduction of nutrients and organic matter into a water
body. Through the use of biological vegetative filters, most of the
sediment and oxygen-demanding organic matter can be removed before the
runoff reaches the water body. Livestock runoff should never be allowed
to drain directly into a water body without first passing through a
vegetative filter.
The water user must remember that the better the water guality, the
cheaper its cost and the fewer the problems that will arise. The poorer
the water quality the more algae and hence the greater the problems with
irrigation intakes, pumps, delivery systems and sprinkler nozzles. Poor
water quality also means more expense in setting up and maintaining a
farm and ranch domestic water treatment facility. Poor water quality
also means greater aquatic plant problems which contribute to increased
water loss through evapotranspiration and increased water temperature.
With increased water temperatures there is increased algal and bacterial
growth which creates odor and taste problems as well as potential toxic
water problems.
19 -
AQUATIC VEGETATION MANAGEMENT TECHNIQUES
Non-chemical techniques
The mechanical methods of aquatic plant removal developed over the years
all seem to neglect the fact that aquatic plants have the capacity to
reproduce vegetatively from stem fragments, specialized stem apices,
tubers, stoloniferous rhizomes, axcillary tubers and runners. Cutting,
chaining, dredging or drag-lining, and pulling all tend to leave the
root system, the crown at the substrate, and usually part of the
vegetative plant intact. Regrowth begins immediately and with the
healthy root system the plant grows even faster. In the case of
cutting, the underwater plant becomes more bushy, increasing the
potential for more turions and overwintering apices. Timing the cutting
to remove the vegetative top growth before the tubers have developed and
hence before there is a reserve food supply in the plant can be very
effective in controlling some rooted submerged macrophytes. Combining
the removal of the excessive vegetative top-growth or 'standing crop' of
the aquatic plant population with timely injection of herbicides
underwater, just above the new regrowth, will kill the plant back to the
substrate and in some cases may even destroy the crown and root system.
Dredging or drag-lining is used extensively in the irrigation conveyance
systems of southern Alberta but this has a tendency to spread the plant
tubers. Mud and water that escape in the dredging operation spread a
thin layer of nutrient-rich substrate and numerous tubers and rhizomes
along the canal. These catch in crevices and give rise to new
infestations.
Recently, new machines such as rotovators and hydro-jets mounted on
barges have been designed and prototypes tested to dislodge the tubers,
rhizomes, root systems and crowns from the muddy sediments. These
research machines are in the experimental stage but may offer some
long-term control once the design has been perfected. The important
aspect of this engineering is that we are recognizing the significance
of destroying the root systems. For control of aquatic weeds the plant
must be dislodged from the substrate and then collected and removed from
the water.
Habitat manipulation
Aquatic vegetation is only the visible symptom of a deeper underlying
problem or cause. Aquatic plants can be harvested from now until the
end of time but they will always grow back. They can never be
eradicated because of their fantastic vegetative reproductive ability.
A single plant can colonize a pond, reservoir or canal system in three
to five years. Once established in a freshwater environment, the
aquatic plants not only spread through that system vegetatively but form
- 20 -
seeds that can then be spread to other systems by migrating duck and
geese.
We must learn to manage the growth of aguatic vegetation and control the
spread of aguatic weeds in our freshwater systems. By designing our
freshwater ecosystems to limit the sunlight, manage the water
temperatures to maintain cool water, restrict the inflow of necessary
plant nutrient and prevent the accumulation of rich organic sediments
necessary for the rooting of aguatic macrophytes, we can do much to slow
up the establishment of overabundant aguatic weeds. A healthy aguatic
environment actually reguires some vegetation to support the aguatic
invertebrate populations and a viable sport or commercial fishery.
Water level manipulation has long been one of the most often practised
but least understood technigues. Certainly the lowering of the water
level in the winter will achieve a degree of control through the
freezing of the exposed crowns. Recent studies have shown that there is
a minimum freezing period of 60 days and a minimum temperature of -10°C
to kill tubers of P. pectinatus. It is probably safe to assume that
each aguatic plant species has its own specific temperature
reguirements . Dormant apices and turions of a number of species appear
to be much more resistant to low temperatures but less tolerant of
desiccation. Preliminary studies suggest that the combination of
freezing and desiccation proves much more effective for aguatic plant
species with specialized overwintering vegetative structures that lie
within the top 5.0-7.5 cm of the sediment surface.
A drawdown treatment in the summer for periods as short as 10 days
appears to achieve good control through the desiccation of the aguatic
plant tops, crowns and shallow root systems. This has been seen in
irrigation canals and along pond banks during the last few drought years
on the Prairies. Generally, the peak demand is for summer water but
alternate storage sources could be designed to permit occasional summer
drawdowns. Success is only achieved if the sediments are dried out. An
elevated water table or saturated sediments prevent the aguatic plants
from being killed.
Related to this is the increasing of the pond or dugout water level to
flood out or drown aguatic plants at the beginning of the flowering
stage of the life cycle. Studies have shown that pondweeds such as P.
richardsonii, P. illinoisis, P. pectinatus and P. zosteriformis can be
killed by raising the water level 5.0-8.0 cm above the plant tops after
the plants begin to initiate flowering but before the flower buds open.
This is attributed to the disruption of the final stages of the life
cycle with the initiation of flowering and the approaching senescence
stage. The increased water depth does not permit the plants to complete
the flowering and seed development stages and the vegetative stage is
completed. However, since tuber formation has already taken place, this
technigue will do nothing towards alleviating the following years'
problems .
- 21 -
The introduction of cool water can slow the growth of rooted submerged
aquatic macrophytes. Another technique is to circulate the water
throughout the water body by moving colder water from deep in the pond
or lake up to the surface by aeration. Stagnant water tends to be
warmer because of summer heating and in shallow water bodies this
stimulates vegetative macrophyte and algal growth. If colder water can
be circulated through the entire pond and moved from deeper water to the
shallower areas, the cooling effect will inhibit aquatic vegetative
growth. Oxygenation through aeration is also beneficial with the
cooler, more oxygenated water restricting the growth of some
phytoplankton species.
Although research is lacking on the effect of oxygen levels in the water
column on the growth of macrophytes, it is known that low oxygen levels
stimulate algae production. Blue-green phytoplanktonic algae prefer
warmer water temperatures (above 22°C) and oxygen levels below 2.0 ppm,
whereas filamentous algae prefer oxygen levels above 5.0 ppm. Thus the
use of aerators to mix, cool, and oxygenate the water all assist in the
reduction of some nuisance aquatic vegetation. In western Canada the
use of wind power has proven effective in running air compressors which
supply air to air stones located on the bottom of dugouts, ponds and
small irrigation reservoirs which aid in the cooling, circulation, and
aeration of farm and ranch freshwater ecosystems. All these habitat
improvement techniques make the aquatic ecosystem that much better for
the growth and development of aquatic organisms including fish species.
Biological control
Aquaculture has been practised in many countries of the Old World and in
Asia to supply food to the local inhabitants. The principles are based
on maintaining a healthy and balanced aquatic ecosystem. The prime
function of aquaculture in Israel is to grow sufficient fish to meet the
demand for 20-25 kg per person per year. Through the careful selection
of specific fish species it is possible to establish a polyculture
which will utilize the entire water column from surface to substrate.
It is even possible to select species that will feed in the mud of the
pond bottom. The incorporation of other aquatic organism such as eels,
shrimp and mussels permits the further purification of the water.
Research in Israel and Germany has shown that aquatic vegetation and
aquatic organisms can be used to purify water after domestic use.
In North America we grow enough food on the land so our freshwater
resources have been used primarily for recreation, but the increased
population growth has still put intense pressure on the aquatic
ecosystems and the surrounding watersheds. This is seen in the nutrient
enrichment of our waterways and the subsequent proliferation of aquatic
vegetation and the deterioration of much of our surface water quality.
In Canada aquaculture can be used to restore and maintain a healthy and
balanced aquatic ecosystem and provide the added advantage of supplying
- 22 -
fish protein. We cannot expect to maintain our freshwater resources in
the pure primitive state while using our land intensely to support our
present population. We must look at every available technology to
improve and maintain our freshwater resources. In Canada there seems to
be a real potential for biological control of aguatic vegetation.
Since the mid-1960s extensive research has been conducted around the
world on the use of herbivorous organisms to harvest and control aguatic
vegetation. Most of the research has been directed towards the
determination of the efficiency of the white amur fish ( C tenopharyngodon
idella) as a biological control agent for controlling noxious aguatic
weed growth. Emphasis has been on the evaluation of the effects of
space and plant nutrients resulting from the destruction of excessive
weed growth in the aguatic ecosystem.
The Netherlands has about 150,000 ha of surface water, much of it in
canals and drainage ditches. Filamentous algae create the major
problems, but these waterways also contain extensive populations of
higher plants. The Dutch started to investigate the potential for the
use of the white amur or grass carp in 1966 with the importation of fish
from Hungary and Taiwan. The impact studies in the Netherlands showed
that the fish caused less ecological damage than herbicides and that
dramatic changes in water guality did not occur. Czechoslovakia has
been importing the white amur from Russia for the control of rooted
aguatic macrophytes since the mid-1960s.
Austria has used the white amur since the early 1970s and has stocked
most of its lakes and ponds with the fish. It has been in major
Austrian river systems for the last 16 years without reproducing
naturally. In West Germany the stocking of white amur has proven not
only economical and cheaper than herbicides but environmental impact
studies on the effect the grass carp has on native fish species have
shown that the survival and growth of native species have not been
adversely affected.
In North America the U.S. Army Engineers Waterways Experiment Station
has been planning and conducting large-scale operations and management
tests using grass carp to control aguatic plants such as hydrilla
(Hydrilla verticillata) in the state of Florida. Their original
research was concerned with the efficiency of the diploid fish as well
as the long-term effect of the fish on the water guality. In 1980, the
Bureau of Reclamation, Division of Research entered into a cooperative
agreement with the U.S. Fish and Wildlife Service, The California
Coachella Valley Water Users Organization, the Imperial Irrigation
District of California and three State of California agencies to conduct
research into the evaluation of the sterile triploid white amur for
controlling aguatic weeds in the irrigation canals in southern
California.
- 23 -
The favorable results from these studies prompted the Province of
Alberta to establish a research committee on the potential use of
biological organisms such as sterile grass carp to control aquatic
vegetation in southern Alberta irrigation canals. The Committee is
composed of representatives from the Alberta Fish and Wildlife Division,
the Vegreville Environmental Research Centre, and the Pollution Control
Branch of the Alberta Department of Environment; the Alberta Department
of Agriculture, Irrigation Planning Division; Agriculture Canada,
Lethbridge Research Station; and the Irrigation Projects Managers
Association of southern Alberta. The research project is investigating
certified imported stocks of grass carp fry under quarantine for
potential diseases and parasites and studying their growth and
development under laboratory conditions. The field studies will
determine the seasonal water quality and vegetative biomass of selected
southern Alberta irrigation canals before and after the introduction of
sterile grass carp. Investigations will include the growth and survival
of these fish under Alberta climatic conditions.
If these studies prove successful then further research into the
potential for the use of other herbivorous organisms such as other fish,
snails, and crayfish should be conducted. Studies on the harvesting and
marketing of the grass carp as a source of fish protein for human food
and as food supplements should be conducted.
Chemical (herbicide) control
Excessive aquatic weed infestations can be killed, controlled, or
maintained at acceptable plant population densities through the use of
aquatic herbicides and plant growth inhibitors. They offer an effective
way to restore the flow rate of water through irrigation conveyance
systems. Generally, the management of nuisance aquatic plant biomass is
easiest and most economical through the use of aquatic herbicides.
However, chemical management techniques are usually short-term, lack
target plant specificity, may have undesirable side effects on other
aquatic organisms, and be toxic to specific aquatic animals. The
aquatic herbicide program is only a treatment and not a cure. Hence,
once the herbicide program is started, it must be continued on a yearly
basis.
Before any aquatic herbicides are applied to water the applicator must
become familiar with the federal, provincial and local regulations.
Only federally licensed herbicides may be used and the label
restrictions must be followed. Standard safety precautions must be
followed and particular care must be taken to avoid herbicide spillage
where children and pets may come in contact with the herbicide. In
public waters a provincial permit is required and the applicator must be
licensed by the province.
- 24 -
The small 13.5-22.5 liter garden pressure-type sprayers available from
most hardwares, garden supply stores, and farm supply centres are more
than adequate for treating small ponds, dugouts, and irrigation
conveyance systems. For ponds and lakes greater than 5-10 ha the use of
larger commercial or farm field-type sprayers is recommended. In many
cases the sprayer with its tank and pressure system can be loaded onto a
flat-bottom boat or pontoon boat with a small outboard motor and be used
for lakes up to 50 ha in size. It must be remembered that a large body
of water cannot be treated at one time. Generally, no more than 10 to
20 per cent of the surface area should be treated at one time with
successive treatments every third day. This is to prevent a massive
oxygen depletion from the decaying aquatic vegetative biomass that is
knocked down by the herbicide. Thus, large sprayers and large boats are
of little value in aquatic herbicide spraying.
Granules can be spread by hand-operated, crank-type seed or fertilizer
spreaders for spot treatment of areas around boat launching sites,
docks, and swimming areas. Large commercial versions are available for
tractor power takeoff or battery operation but again the goal should not
be to see how much can be done in one day but to treat a small area very
uniformly with no skips or excess material applied at any point.
Helicopters have been used in the United States for liquids and granules
but it is impossible to see any such application in Canada because of
the diversity of our aquatic environments, the diversity of our
irrigated crops, and the multiuse concept of our aquatic ecosystems.
Aquatic herbicide applications should start near the shore and move out
into deeper water so that fish and other aquatic organisms are driven
out of the treatment area. Particular attention must be paid to inflow
areas since the herbicide must have sufficient contact time with the
aquatic vegetation to permit absorption. Inlets and spillways must be
closed and the treated water generally ponded for a minimum of three
days before it is allowed to flow out of the area.
Where possible, the aquatic herbicide treatments should be made in the
late spring or early summer when the aquatic plants are young and
actively growing. In the case of emergent vegetation, applications must
be made at the early inflorescence stage before the plants begin to
flower. Treatments must be made on calm days to avoid the possibility
of spray drift. It has been found that late evening applications allow
the herbicide to mix through the water column and be absorbed more
readily by the aquatic vegetation during darkness. This also applies to
the application of herbicides to emergent, floating-leaved and ditchbank
vegetation where the herbicide is absorbed by the plant tissue and
translocated down the stem and into the rootstocks during darkness.
ALGAE
The most common algae problems are from filamentous algae in dugouts and
irrigation reservoirs where they cause stagnation and plug intake
- 25
screens, pumping systems and nozzle heads in irrigation delivery
systems. Phytoplanktonic algae are usually associated with domestic
water supply reservoirs and small farm and ranch systems. Here the key
to success is the early application of herbicides before the algal
population becomes dense since early application will have a better
chance of getting the entire infestation and will enable the water
manager to use less herbicide and hence be more economical. The water
manager must check the pond or irrigation reservoir daily since an algal
bloom may appear overnight. Algae exist in the water column all year
round but under cool water temperatures they exist near the bottom of
the water body. As the water temperature warms and the sunlight begins
to penetrate beneath the surface of the water, the algae begin to grow.
As the water temperature approaches the 22 °C point, growth is greatly
accelerated and the scums and dense floating mats begin to appear at the
surface of the water. In the spring, daily checks should be made of the
water bodies and daily microscopic examination of surface and subsurface
water samples is an excellent practice for domestic reservoir water
managers. Although every water body is different, water managers can
generally become acquainted with their own systems. Through experience
they will learn to anticipate when the critical first treatment in the
spring is necessary and then read the seasonal signs for possible
retreatment.
The herbicide used and the dosage required will depend on the type of
algae involved, the degree of infestation, the water chemistry of the
pond or reservoir, and the use to which the water is put. Appendix I
lists the herbicides registered for algae control and the restrictions
placed on each chemical. On the Prairies, the surface water is
generally hard with a pH in the high 7 to mid 8 range and will require
lower dosages applied in split treatments three to four times per
season. For a split treatment, the recommended dosage is divided in
thirds and applied as a surface spray every second day over a one-week
period. This split treatment is also a good idea where trout are in the
pond since trout are very sensitive to copper sulfate at levels above 1
ppm. Early treatment before a dense algae population occurs will ensure
that when the algae are killed there is no serious oxygen depletion.
The destruction of the algal population and the subsequent decay of the
algal organic matter can cause a serious drop in the dissolved oxygen
content of the water column. If this starts to occur it may be
necessary to provide supplementary oxygen by aeration. Aeration cools,
circulates, and oxygenates, making a healthier aquatic ecosystem.
SUBMERGENT MACROPHYTES
The submergent aquatic plants spend their entire life cycle beneath the
surface of the water, except during flowering and pollination. The key
to successful herbicide control of these plants is to apply the
herbicide when the plants are actively growing and before the vegetative
biomass becomes too great. This means applying the herbicide beneath
- 26 -
the surface of the water just above the growing tip. With granules this
is a simple matter but with liquid herbicides this requires the
injection of the material underwater. A pressure-type application
system and an extension system to permit delivery of the herbicide
1.0-1.5 meters underwater must be used. The herbicide should be diluted
with 5-10 parts of clean water to permit uniform application of the
material to the test area. Remember that beneath the surface of the
water there is very little water movement so the application should be
made in a criss-cross manner, north to south first and then east to
west. It has been found at the Lethbridge Research Station that evening
applications permit the herbicide to diffuse through the water column
and to be more uniformly absorbed by the submergent aquatic plants.
Evening applications also permit a reduction in the herbicide dosage by
up to 25 per cent.
For large water bodies, spot treatment or channel cutting is a very
effective way to reduce the aquatic nuisance population and at the same
time not create serious oxygen depletions from massive weed kills.
Remember, if it has taken many years to build up a serious aquatic weed
infestation, it cannot be corrected with one massive herbicide
treatment. Plan the control program to remove the aquatic infestation
for 3-5 years and the management program for another 2-4 years.
FLOATING-LEAVED MACROPHYTES
Floating-leaved aquatic plants such as water lilies and water smartweeds
are valued by fishermen and outdoor enthusiasts but may cause serious
problems when they take over a pond or boating area. Herbicides must be
applied to the actively growing leaves by surface spraying. It is best
to add a wetting agent to the herbicide mixture to ensure uniform
coverage and hence maximum absorption of the herbicide. Spray to the
point of runoff. Evening spraying has proven effective since the
herbicide is absorbed and translocated down the stems to the underwater
tubers before the plants are exposed to sunlight again.
FREE-FLOATING MACROPHYTES
The free-floating aquatic plants such as the bladderworts, coontail,
some buttercups and the duckweeds must be surface-sprayed but without
the addition of wetting agents. The plants exist in the upper 12 cm of
the water column and will absorb the herbicide from the water. Evening
spraying has proven very effective on the Prairies. The lowest
recommended dosage should be used since the plants appear very sensitive
to all registered aquatic herbicides.
- 27 -
EMERGENT MACROPHYTES
Emergent aquatic plants grow in moist, water-saturated, swampy shoreline
areas and extend out into the water to a depth of 30 cm from the shore.
Most emergent plants are greatly valued by wildlife for food and
shelter. They also stabilize the shoreline and banks to prevent water
erosion. Before any control program is started, the long-term impact of
vegetation removal must be examined. Foliar herbicide sprays should be
applied in the early summer at the time of emergence of the flowers or
inflorescences. At this time there is a narrow one-month period when
the translocation of photosynthates in the plant is down from the leaves
into the tubers and this is the most effective time for herbicide
application to achieve total plant kill. Depending on the season, this
is usually from the 15th of June to the 15th of July with effective
control dropping off during August to almost no control in September.
During this 'window' period it is necessary to have maximum absorption
of the herbicide and so additional wetting agent must be added to the
spray mixture. The spray must be applied to the point of runoff and
every leaf must be thoroughly covered. Cattail control has been
improved by evening applications so the herbicide is absorbed overnight
and translocated in the carbohydrate stream down into the tubers. This
is particularly true when using the herbicide Gramoxone.
MARGINAL OR DITCHBANK WEEDS
Many of the marginal and ditchbank plants are valuable plants for
waterfowl and wildlife as shelter for nests and cover for the young.
They also prevent bank erosion and act as vegetative biological filters
to prevent the introduction of sediments and nutrients from surface
runoff. At times it may be desirable to remove the vegetation from the
bottom of the canal bed but leave the grass species on the upper inner
banks and over the tops of the banks. Here the foliar application of a
herbicide should be made in large volumes of water and sprayed to the
point of runoff. The addition of a wetting agent will assist in
ensuring uniform coverage and maximum herbicide absorption.
For the control of terrestrial weeds the manager should use the
recommendation for the control of weed species used by farmers but must
exercise care to avoid the contamination of irrigation water by
overspray and spray drift.
The use of the wick applicator is excellent since the weeds are wiped
with the herbicide-saturated wick and there is no chance of herbicides
getting into the irrigation water. The wick applicator also permits the
treatment of tall weeds while leaving the low-growing grasses
untouched. This retains the grasses for ditchbank stabilization and
surface runoff filtration.
- 28 -
WATER QUALITY IN RELATIONSHIP TO AQUATIC PLANT GROWTH
Water quality is just begining to be recognized as important not only to
the development of aquatic vegetation but also to the effectiveness of
aquatic herbicides. Much more research is necessary before the full
role of the nutrients in the water column and the sediments is
understood. Knowledge of the effect that seasonal variations in
nutrient content have on the growth and development of algae and aquatic
macrophytes is just beginning to enable us to establish guidelines for
freshwater lakes, reservoirs, dugouts and irrigation conveyance
systems. It is wise for all water users and water managers to start
accumulating a database on their aquatic systems now. At least one
sampling should be made every spring, midsummer, early fall and once
through the ice in midwinter. These measurements will enable the
manager to compare the water quality from year to year and should
provide advanced warning of potential problems. Summer measurements
will assist in the better utilization of aquatic herbicides under
varying levels of pH, electrical conductivity, water hardness, soluble
salts concentrations, and total solid and total dissolved solid
concentrations. This information is also useful when designing and
installing domestic water filtration and purification systems.
- 29 -
SELECTED REFERENCES
Allan, J. R. and Braglin-Marsh, J. A.. 1987. Chemical analysis of
surface and irrigation water in relation to aquatic plant management.
Technical Bulletin 1987-1-E. Research Branch, Agriculture Canada,
Ottawa.
Bardach, J. E., Ryther, J. H. and McLarney, W. 0. 1972. Aquaculture.
The farming and husbandry of freshwater and marine organisms.
Wiley-Interscience Publications, John Wiley and Sons, Toronto.
Bennett, G. W. 1971. Management of lakes and ponds. Van Nostrand
Reinhold, New York.
Fasset, N. C. 1966. A manual of aquatic plants. The University of
Wisconsin Press, Madison, Wisconsin.
Gangstad, E. 0. 1986. Freshwater vegetation management. Thomas
Publications, Fresno, California.
Gunnison, D., Barko, J. W. 1988. The rhizosphere microbiology of
rooted aquatic plants. Miscellaneous Paper A-88-4. U.S. Army Engineers
Waterways Experiment Station, Vicksburg, Mississippi.
Mackenthun, K. M. , Ingram, W. M. and Porges, R. 1964. Limnological
aspects of recreational lakes. U.S. Department of Health, Education,
and Welfare, Public Health Service Publication No. 1167. U.S.
Government Printing Office, Washington, D.C.
Mitchell, R. 1972. Water pollution microbiology. Wiley-Interscience
Publications, John Wiley and Sons, Toronto.
Moultonn, F. R. (ed. ) 1939. Problems of lake biology. Publication No.
10/ American Association for the Advancement of Science. The Science
Press, Lancaster, Pennsylvania.
Reid, G. K. 1961. Ecology of inland waters and estuaries. Reinhold
Publishing, New York.
Rutter, F. 1953. Fundamentals of limnology. University of Toronto
Press, Toronto.
Sculthorpe, C. D. 1967. The biology of aquatic vascular plants.
Edward Arnold (Publishers) Ltd., London.
Soil Conservation Service. 1971. Ponds for water supply and
recreation. Agric. Handbook No. 387, U.S. Department of Agriculture.
U.S. Government Printing Office, Washington, D.C.
Warren, C. E. 1971. Biology and water pollution control. W. B.
Saunders Co., Toronto.
- 30 -
Welch, P. S. 1952. Limnology. McGraw-Hill Book Co., New York,
Wetzel, R. G. 1975. Limnology. W. B. Saunders Co., Toronto.
- 31 -
APPENDIX I
The use of chemicals in aquatic ecosystems is subject to federal
registration of the herbicide and then provincial regulations as to
their use, mode of application, restrictions on using treated water and
waiting periods before treated water can be used for irrigation,
livestock watering or human consumption. Contact provincial authorities
to obtain regulations and permits where necessary. The labels must be
read carefully and followed. All necessary health regulations must be
followed to protect the applicators and the general public.
ACROLEIN
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rates:
Time of application:
Restrictions:
2-propenal
Submergent
Contact herbicide causing disruption of
cell enzyme systems.
Irrigation ditches - moving water
Injected beneath the water at 0.6-11 L/cm
(0.12-2.3 gal cfs) applied over 0.5-4.0
hours.
Apply when plants are young and water
temperature is over 20°C.
Treated water must not be used for
drinking water or released into sources of
drinking water.
AMITROLE
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rate:
Time of application:
Restrictions:
1H-1, 2,4-triazol-3-amine
Emergent
Inhibits photosynthesis and regrowth from
buds; slow absorption but good
translocation throughout plant.
Drainage ditches and marsh areas
Foliar spray to the point of runoff in 45
L of water with additional wetting agent
at 2.25-11.2 kg/ha.
Early infloresence stage to appearance of
mature flower head.
Avoid contaminating drinking water
supplies and spray drift onto other crops.
AQUASHADE
This is a water-soluble dye that suppresses algal growth by reducing the
penetration of sunlight into the water column. Its use is only
practical in fountains and small ornamental water gardens.
- 32 -
COPPER CHELATES
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rates:
Time of application!
Restrictions:
8% copper as copper ethylenediamine or
copper triethanolamine complexes
Filamentous and planktonic algae
Acts as general cell toxicant. Copper
chelate is absorbed from the water column.
Farm ponds and dugouts - standing water
0.2 5-1.0 ppm applied to the water column
as a surface spray. Split treatments
applying 1/3 of the dosage every second
day may prove more effective and safer
when fish are in the pond.
Apply at FIRST sign of algae. Early
application permits lower dosages to be
used.
Not for use in public or potable water
systems.
DALAPON
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment!
Dosage rates:
Time of application:
Restrictions:
2, 2-dichloropropanoic acid
Emergent
Absorbed by roots and foliage and
translocated throughout the plant.
Accumulates in young tissue and buds.
Drainage ditches and marsh areas
Foliar application at 11.2-22.4 kg/ha in
450 L water with additional wetting agent
sprayed to point of runoff.
Early inflorescence to mature flower head.
Do not spray in high winds; avoid spray
drift. Formulations mildly corrosive so
wash equipment throughly.
DICAMBA
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment;
Dosage rate:
3 , 6-dichloro-2-methoxybenzoic acid
Emergent (cattails)
Selective herbicide absorbed and
translocated from both the leaves and
roots with translocation to the apical
meristems. Growth-hormone type of
activity causes defoliation, swelling of
stems, destruction of conductive tissue,
death of growing points and necrosis of
the plant.
Marshes, swailles, swampy areas
Cattails require 4-6 kg/ha dicamba plus 6
kg/ha of dalapon.
- 33 -
Time of application:
Restrictions:
Apply at early growth stages up to the
early inflorescence stage, wetting foliage
to point of runoff.
Avoid direct application to water bodies
and do not use treated water for
irrigation for 14 days or for livestock
for 7 days.
DICHLOBENIL
Chemical name:
Type of plants controlled:
Mode of action:
Type of aguatic environment;
Dosage rate:
Time of application:
Restrictions:
2, 6-dichlorobenzonitrile
Submergent, floating-leaved and emergent
Nonselective herbicide absorbed mainly by
the roots but with some absorption by
submerged stems and leaves. Disrupts
plant cell division in the growing tips
causing death.
Ponds and ornamental water gardens
Applied to dewatered pond beds at 5.5-17
kg/ha or as granulars spread over the
surface of the water which sink through
the water column.
Apply to dewatered pond, reservoirs and
shorelines in early spring before aguatic
plant growth begins. May be applied as a
granular formulation spread over the
water's surface from a boat.
Treated water should not be
irrigation, livestock watering,
consumption. A 90-day waiting
reguired prior to the use of
treated waters.
non-selective and may
vegetation.
used for
or human
period is
fish from
Herbicide is
kill shoreline
DIQUAT
Chemical name:
Type of plants controlled;
Mode of action:
Type of aguatic environment;
6,7-dihydrodipyrido[l,2-a:2 ' ,l'-c]
pyrazinediium ion
Submergent, free-floating, floating-leaved,
emergent, and filamentous algae
Contact type, non-selective, rapidly
absorbed by foliage but very little
transloction. Forms a free radical in the
plant that is readily reoxidized releasing
very active free radicals such as
peroxides within the plant cells.
Drainage and irrigation canal, farm ponds
and dugouts, reservoirs and lakes
- 34 -
Dosage rates:
Time of application:
Restrictions
2.25-4.50 kg/ha in 45 L of water injected
underwater for submergent vegetation
or surface-sprayed for free-floating,
floating-leaved or filamentous algae.
Evening applications assist in mixing
throughout the water column giving uniform
coverage and better absorption by the
plant material before herbicidal activity
begins in daylight.
Must be applied after the green plant
material begins to show in the water but
before the plants begin to flower and
become encrusted with marl. Water
temperature should be 20°C.
Do not use treated water for irrigation
for 5 days or until chemical analysis
shows less than 0.01 mg/L Diquat ion. Do
not apply to muddy water or to plants
heavily encrusted with marl or mud. Do
not apply in high winds and avoid spray
drift to food forage or desirable
vegetation. Applicators should exercise
extreme caution in handling Diquat.
DIURON
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rate:
Time of application:
N' -(3,4-dichlorophenyl) -N,N-dimethylurea
Ditchbank grasses and broadleaf deep-
rooted weeds
Herbicide is readily absorbed through the
root system and translocated upward into
the plant. Disrupts the Hill reaction in
the plant cells.
For general weed control in drainage and
irrigation ditches where the ditch beds
are intermittently filled and drained.
For total annual weed control apply at
4.48-12 kg/ha and for grasses and
deep-rooted perennials at 12-35 kg/ha.
Higher rates will give 3-5 years control.
Apply in 450-900 L water to ensure uniform
coverage of area to be treated.
Apply to dry canal beds in the fall before
freeze-up. Adsorption increases as clay
content and organic matter content of soil
increase. Leaching from treated soils in
the spring flush is greatest from sandy
soils.
- 35 -
Restrictions:
Be sure to flush the canal with irrigation
water in the spring before using ANY water
for irrigation.
ENDOTHALL
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rate:
Time of application:
Restrictions:
7-oxabicyclo[2, 2, l]heptane-2/3-dicarboxylic
acid as dipotassium salt
Submergent vegetation
Contact type herbicide that inhibits
protein synthesis. Very limited trans-
location throughout the plant.
Lakes, farm ponds and dugouts
72-119 L/ha as a liquid and 374-631
kg/ha. Herbicide must remain in contact
with the target plants for 2 hours.
Apply to young, actively growing
vegetation when water temperature is at
least 18°C.
Do not use treated water for irrigation
for 7 days, do not use for livestock or
domestic use for 7-14 days, do not swim in
the water for 24 hours and do not eat fish
from treated water for 3 days. Applicators
should use due care and read all label
instructions.
GLYPHOSATE
Chemi c al name :
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rate:
Time of application:
N- ( phosphonome thy 1 ) glyc ine
Emergent aquatic vegetation and green
ditchbank vegetation
The herbicide apparently disrupts the
biosynthesis of phenylalanine and other
aromatic compounds in the growing plant.
Dry drainage and irrigation canals and
shorelines for cattails and general weeds
and brush
Emergent vegetation at 7.0 L/ha hectare
sprayed to the point of runoff. Ditchbank
vegetation at 5.3-8.8 L/ha applied to
green foliage.
When vegetation is actively growing and
with emergent aquatic vegetation, best
results are obtained in the early
inflorescence state until the beginning of
the mature seed head.
- 36 -
Restrictions:
Avoid spray drift and direct application
to surface of water. Do not use
contaminated water for irrigation or
livestock use. Do not apply within 0.8 km
upstream of domestic water intake. Do not
exceed the 8.8 L/ha rate. Effects on
target plants may not appear for up to 4
weeks depending on the growth stage of the
plants .
MCPA
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rate:
Time of application:
Restrictions:
(4-chloro-2-methylphenoxy) acetic acid
Emergent aquatic vegetation and ditchbank
weeds and brush
Selective broadleaf foliage herbicide
acting as a growth regulator absorbed
through the foliage and readily
translocated throughout the plant.
Generally accumulates and is active in the
meristematic tissue.
Dry drainage and irrigation canals and
along shorelines
0.6-1.12 kg/ha applied as a low volume
spray in 9-100 L water with additional
wetting agent.
Apply to actively growing plants where the
herbicide is in contact with the plant for
2-4 days. Herbicide is readily washed off
by rain.
Avoid spray drift and contamination of
adjacent water bodies.
PARAQUAT
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment;
Dosage rate:
1,1' -dimethyl-4,4 ' -bipyridinium dichloride
salt
Submergent, free-floating, floating-leaved
and emergent vegetation
Contact type of herbicide absorbed by the
foliage; may be translocated via the xylem
under certain growing conditions.
Emergent vegetation and as a 1:1 mixture
with diquat for submerged vegetation
General emergent control at 0.6-1.12 kg/ha
with a compatible surfactant. For
submerged vegetation injected underwater
as a 1:1 mixture with diquat at 4.5-9.4
L/ha mixed 10:1 with clean water.
- 37
Time of application:
Restrictions:
Apply in the late spring to early summer
when the plants are actively growing.
Treat before the biomass gets too great.
For submerged vegetation inject underwater
to the area just above the growing plants
and criss-cross the plot to ensure uniform
coverage. Evening application to emergent
and submerged aquatic vegetation seems to
improve herbicide uptake.
For emergent vegetation avoid spray drift
and contamination of standing water. Do
not use treated water for irrigation for 5
days or until chemical analysis shows less
than 0.01 mg/L. Do not apply to muddy
water or to plants heavily encrusted with
marl or mud. Do not apply in high winds
and avoid spray drift.
SIMAZINE
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rate:
Time of application:
6-chloro-N,N' -diethyl-1, 3, 5-triazine-2,4-
diamine
Used as a selective herbicide for the
control of broadleaf and grassy weeds in
perennial grasses used for ditchbanks and
as non-selective control of all vegetation
in the canal bottoms of intermittently
filled and drained irrigation canals in
community pastures.
Herbicide is absorbed through the roots
with little foliar absorption.
Translocated to the apical meristematic
tissue where it inhibits photosynthesis.
Dry drainage and intermittently filled
irrigation canals. Beach area above the
high water level.
For selective control of broadleaf weeds
in established grasses apply at 2.0-4.5
kg/ha in 80-100 L of water to ensure
uniform coverage. For total vegetation
control apply in the fall to dewatered
canal bottoms at 15-22 kg/ha in 150-200 L
water to ensure complete coverage. Do not
treat above the usual operating water
level of the canal.
Generally apply to bare soil as herbicide
must be root-absorbed. For total
vegetation control apply in the fall just
before freeze-up. The winter moisture
will wash the herbicide into the soil
where it will be bound in the top 10 cm of
soil.
- 38 -
Restrictions:
Simazine is strongly adsorbed on clay and
muck soils with little leaching downward
due to its low solubility in water. To be
safe, the first irrigation water in the
spring should be flushed out of the system
and wasted. Carefully and correctly
applied herbicide to the canal bottom will
give 3-5 years control before retreatment
is necessary. Subsequent treatments at
5-10 kg/ha generally restore weed control
for another 5 years.
2,4-D
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
Dosage rate:
Time of application:
Restrictions:
2.4-D as dimethylamine salt (liquid)
Emergent aquatic plants and broadleaved
weeds and brush
Selective as a systemic growth regulator
with hormone-like activity. Readily
absorbed from the roots and foliage and
translocated throughout the plant.
Inhibits or stimulates cell division in
meristematic tissue causing necrosis in
young tissue and death in mature tissues.
Dry drainage and irrigation ditches
Canal bank vegetation at 1-2 kg/ha;
emergent vegetation at 2-4 kg (active
equivalent ) /ha .
Apply in early spring when vegetation is
actively growing. Additional water and
wetting agent applied to the point of
runoff will assist in the uptake of the
herbicide.
Liquid formulations are for use on
emergent and ditchbank weeds and brush.
Do not spray during high winds and prevent
spray drift to nontarget vegetation. Do
not use contaminated water for irrigation,
livestock watering or domestic use for 3
weeks OR until chemical assays contain
less than 0.1 ppm (0.1 mg/L) of 2,4-D acid.
2,4-D
Chemical name:
Type of plants controlled:
Mode of action:
Type of aquatic environment:
2,4-D as butoxyethanol ester (Granular)
Submergent aquatic vegetation, especially
the water milfoils
Same as above
Drainage ditches and farmponds and dugouts
where water is not used for irrigation
- 39 -
Dosage rate:
Time of application!
Restrictions:
9.5-38 kg/ha using the higher dosage for
heavy infestations.
Apply granulars through the water column
in early spring while the submerged
vegetation is actively growing. Use
criss-cross application methods to ensure
uniform coverage. Plots should be
separated by a buffer, untreated plots of
egual size.
Do not use treated water for irrigation,
livestock watering or domestic use until
chemical assays of treated water contain
less than 0.1 ppm of 2,4-D acid. Contact
local fish and game authorities for
specific restrictions on fishing and
swimming.
- 40 -
Figure 1. Typical prairie aquatic ecosystems. A. Shallow irrigation
reservoir located along the foothills of southern Alberta. B. Main
delivery canal out of Travers Reservoir near Taber, Alberta. C.
Henderson Lake at Lethbridge, Alberta, which serves as an on-stream
irrigation storage reservoir and recreational lake in the center of the
city. D. Typical farm dugout used for livestock watering and
irrigation as well as domestic water after filtration and purification.
- 41 -
Figure 2. Life cycle of the submergent rooted aquatic macrophyte,
Potamogeton richardsonii . A. Vegetative shoot of pondweed. B. Leaf
structure showing the clasping characteristic of the leaf blade around
the stem. C. Flower bud initiation in the axil of leaves underwater.
D. Flower head extended to the surface of the water for wind
pollination. E. Details of the flower head showing formation of a
single seed at the tip of the flower head. F. Young shoots of pondweed
at the sediment surface before water is turned into the reservoir. G.
Young pondweed rhizome taken from 15-20 cm beneath the sediment surface
in the spring. H. Same rhizome 7 days later showing the young plant
vegetative shoot and the horizontal rhizome continuing its growth and
the appearance of young roots at the site of the next vegetative shoot.
- 42 -
Figure 3. Life cycle of the submergent rooted aquatic macrophyte,
Potamogeton pectinatus . A. Vegetative shoot of pondweed. B.
Appearance of the plant in flowing water. C. Appearance of the plant
in standing water growing with other rooted aquatic plant species. D.
Overwintering tuber. E. Sprouting tuber showing root and shoot
development. F. Vegetative shoot showing the runner and the start of a
second plant from the parent tuber. G. Flower head showing the
characteristic space or separation of the first and subsequent flower
whorls. H. Details of the flower head showing flower structure.
- 43 -
Figure 4. Life cycle of the submergent rooted aquatic macrophyte,
Myriophyllum verticil latum. A. Vegetative shoot of water milfoil. B.
Mature plant of water milfoil showing the production of overwintering
buds or turions at the tip of each vegetative branch. C. Appearance of
the plant in flowing water. D. Appearance of the plant in standing
water with other rooted aquatic plant species. E. Stem fragments
showing root development at the base of the shoot. F. Leaf structure
of overwintering turion. G. Typical leaf structure of water milfoil
plant. H. Flower head at the surface of the water. I. Flower head
extending into the air for wind pollination. J. Details of flower head
showing characteristic flower bracts used to identify Myriophyllum spp.
K. Details of Myriophyllum spp. turions.
- 44 -
Figure 5. Life cycle of the free-floating aguatic macrophyte,
Utricularia vulgarius . A. Vegetative shoot completely lacking roots
but possessing small black bladders that assist in the trapping of
aquatic organisms for food. B. Overwintering turion of the common
bladderwort. C. The expansion of the turion in the spring when water
temperature reaches 15°C. D. Details of leaf structure showing the
small bladders. E. The free-floating bladderwort along the shore of a
stock-watering pond showing the showy flower. F. Details of the flower
head. G. Typical habitat of the common bladderwort showing the
numerous flower heads.
- 45 -
Figure 6. Life cycle of the floating-leaved aquatic macrophyte,
Nymphyia odorata. A. The typical plant growing under greenhouse or
ornamental water garden conditions. B. Aerial view of water lilies
growing in lakes in northern Alberta. C. Crown of water lily plant
showing vegetative shoots. D. Tuber of water lily plant showing
extended leaf petiole. E. Water lily plant planted
ornamental water garden. F. Detail of floating leaf
plant. G. Water lily plant with fully open flower. H.
opened water lily flower.
in tub in an
of water lily
Detail of the
- 46 -
Figure 7. Life cycle of the emergent aguatic macrophyte, Typha
latifolia. A. Colony of cattails growing at the edge of a pond. B.
Underground rhizome system showing two vegetative shoots and the root
system. C. Young cattail shoots in 10-20 cm of water. D. Mature
plant showing leaf formation and structure. E. Crown of a mature plant
with root system. F. Early infloresence stage or 'window' when plants
are most susceptible to chemical control showing male flowers above the
female flowers. G. Young flower head with developing female portion
and the male portion above after the pollen is shed. H. Mature cattail
head just begining to shed the wind-disseminated seeds. I. Exploded
cattail seed head with winged seeds ready to be wind-blown to potential
marsh sites.
1IBRARY HIM IOTHEUIJI.
AGRICULTURE CANADA OTTAWA K IA nC5
3 T073 aaat,so?5 b
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