11.1 Introduction
11.2 Structure Provided by Plants
11.3 Influence of Plants on Fish Spawning
11.4 Aquatic Plant Establishment
11.4.1 Plant Selection
11.4.2 Source of Propagule
11.4.3 Propagule Production
11.4.4 Plant Establishment in Reservoirs
11.4.5 Multiple Depths Planting
11.4.6 Post-Planting Monitoring
11.5 Control of Aquatic Plant Growth
11.5.1 Biological Control
11.5.2 Mechanical and Physical Control
11.5.3 Chemical Control Practices
11.5.4 Cultural Control Practices
11.6 Promotion of Terrestrial Plants on Barren Shorelines
11.6.1 Wee-Vegetated Riparian Zones
11.6.2 Seeding
11.6.3 Timing
11.6.4 Seeding Methods
11.6.5 Transplanting
11.6.6 Grasses and Other Herbaceous Plants
11.6.7 Trees and Shrubs

11.1 Introduction

Plants are an important part of healthy, diverse aquatic ecosystems. Specific roles of aquatic plants and terrestrial plants that colonize reservoirs include producing and consuming of oxygen, stabilizing temperature and light, recycling nutrients, controlling turbidity, and providing food, spawning substrate, and habitat for invertebrates and fish. Plants also protect shorelines from erosion, and plant roots stabilize lake-bottom sediment to protect it from the stirring effect of wave action. Additionally, plants are valued for their aesthetic qualities and help provide a more “natural” buffer between the riparian zone and the open water.

Aquatic macrophyte abundance in reservoirs often exhibits two contrasting problems: too many or too few macrophytes. A survey of 1,299 reservoirs ≥250 ac in the USA identified that excessive macrophytes was a concern in nearly 10% of the reservoirs surveyed, and not having enough macrophytes was a concern in over 25% of the reservoirs (Krogman and Miranda 2016). These percentages varied regionally, with excessive macrophytes afflicting nearly 25% of reservoirs in the Coastal Plains ecoregion, and not enough macrophytes troubling over 40% of reservoirs in the Southern Plains and Temperate Plains ecoregions (Figure 11.1).

Three factors commonly preclude development of adequate aquatic plant densities in reservoirs. First, aquatic plant communities may take hundreds or even thousands of years to develop in natural lakes (Doyle and Smart 1993). Because most reservoirs are <100 years old, there has not been enough time to allow the development of a seed bank that can support suitable plant assemblages. Moreover, suitable seed banks may not exist in the reservoir’s watershed. Second, the abiotic conditions in many reservoirs may be too harsh for many aquatic plants. These include high turbidity and large and rapid water-level fluctuations. Third, herbivores, including various fish species, reptiles and amphibians, mammals, birds, crayfish, and insects can prevent the survival of pioneer aquatic plant colonies that eventually may colonize the reservoir.

Macrophytes occasionally can become a nuisance, but how much is too much depends on the reservoir and its use. Some uses of a reservoir are more affected by macrophytes than others, and some types of plants interfere with boating or recreational activities more than others. Generally, plants are not considered to be a problem unless they interfere with desired uses for the reservoir. Some plants have capabilities to become very abundant and are thus apt to become a nuisance. An example is the nonnative hydrilla (Hydrilla verticillata), which is found in a wide range of environments. This plant has a broad tolerance in its environmental requirements and is capable of flourishing under what seems to be difficult conditions. Recreational boaters unwittingly contribute to the spread of hydrilla and other macrophytes by carrying fragments of the plant on their boats, trailers, or fishing gear to other water bodies.

Various problems frequently are attributed to the excessive growth of macrophytes in reservoirs. Oxygen deficiencies due to plant respiration and to decay of deceased plants often are identified as a major problem for various water uses. Excessive protection of prey fish to the extent that normal predator–prey interactions are substantially diminished and alter population dynamics, fish assemblage composition, and possibly fish production are major fishery concerns. Another common complaint is the interference with recreational activities such as boating, water skiing, swimming, and bank angling. Additionally, unsightly and odoriferous accumulations of plant material can develop on the water surface, on beaches, and along property fronts.

Terrestrial plants in regulated zones of reservoirs can provide important habitat to spawning adult fish and juveniles. The regulated zone often turns into bare shorelines or mudflats because of the die-off of flood-intolerant plants, which is caused by annual or semi-annual flooding, wave action, or both (section 7). Some reservoirs, particularly in the West, have steep, bare banks with 100-250-ft drawdowns. Conversely, shallow reservoirs with smaller drawdowns can expose extensive areas encompassing hundreds or thousands of acres and representing a large fraction of the reservoir. These large areas of bare mudflats exposed during drawdowns may be recolonized by terrestrial plants during drought years when water levels remain low but otherwise remain mostly bare and provide low-quality habitat.
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11.2 Structure Provided by Plants

Aquatic vegetation increases the habitat complexity of reservoir ecosystems. An overabundance of plants, however, can interfere with fish feeding. In waters with no aquatic macrophytes, there may be insufficient cover to allow survival of structure- oriented small fish. As vegetation increases to intermediate levels, habitat becomes more complex, invertebrate densities increase, small prey and young predator fish find more refuge from predators, and recruitment into older age groups increases (Dibble et al. 1997; Miranda and Pugh 1997). At high levels of vegetation, especially dense monocultures formed by invasive aquatic species, it is more difficult for fish predators to forage because of the visual barrier or inaccessibility. This lack of access to prey causes overall slower fish growth, favoring small-size fish and reducing the larger fish that commonly make up a fishery. Fish assemblage composition may also shift. Reservoirs with low vegetation densities tend to include a higher abundance of fish species adapted to open-water habitats, whereas reservoirs with a high abundance of aquatic vegetation tend to be dominated by fish species adapted to cover (Bettoli et al. 1993). In addition, many fish that live among aquatic plants are visual feeders, and the shade produced by overhanging leaves and plant canopies improves visual acuity so fish can find prey and avoid becoming prey (Helfman 1981).

Researchers have suggested that a moderate amount of vegetation is optimal for fish production. Vegetation coverage of 20%–80% encourages the formation of stable fish assemblages, and 20%–40% has been reported as optimal (Durocher et al. 1984; Wiley et al. 1984; Miranda and Pugh 1997). This is a relatively wide range, which meets diverse goals of management including maintaining adequate fish and wildlife habitat.
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11.3 Influence of Plants on Fish Spawning

The structure provided by aquatic plants provides important habitat for fish reproduction (Petr 2000). Many fish are obligate plant spawners, directly or indirectly requiring aquatic plants to reproduce. Various fish families use vegetation as nurseries for their young, and reproductive success of nest spawners is improved when they have access to sites with aquatic vegetation, other forms of structure, or both. Fish can derive a number of benefits from nesting near aquatic plants. For example, vegetation can protect nest sites from wave action and sedimentation, which can harm eggs and larvae. Also, parents often use aquatic plant patches or edges as backing to protect nests from predators (Figure 11.2).
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11.4 Aquatic Plant Establishment

Aquatic vegetation is often lacking in reservoirs because of the unnatural fluctuations in water levels and the lack of an established seed bank. A seed bank may take several hundred years to develop in flooded lowlands and may take even longer along reservoir shores where soils originate from uplands (Godshalk and Barko 1985). Also, these upland shores may not be initially suitable for the growth of rooted aquatic plants if soils are hard-packed clay or rocky. To  accelerate establishment of aquatic plants in reservoirs with little or no water-level fluctuations, efforts have been directed at planting native vegetation (e.g., American pondweed Potamogeton nodosus and wild celery Vallisneria americana) in exclosures to produce founder colonies (Smart et al. 1996). Exclosures are critical because small patches of transplanted plants or propagules growing along a barren shoreline quickly will be grazed by terrestrial, aquatic, amphibian, and avian herbivores (Smart et al. 1998). Although the prospect of establishing native plants is appealing because of their potential to transform fish habitat, such programs have had mixed success. Exclosures are prone to failure when they are forcibly entered by turtles and other grazers, and plants that expand outside the exclosures are often cropped by herbivores. Nevertheless, successful establishment of aquatic macrophytes in some reservoirs may be possible (Webb et al. 2012).

Establishment of aquatic plants has had some success through the establishment of a small, protected start-up of high-quality propagules, such as mature transplants, at strategic locations in the reservoir (Webb et al. 2012). This founder colony provides propagules that may allow expansion of the vegetation into a large section of the reservoir. The founder colonies expand through direct vegetative spread and through formation of new founder colonies from fragments or seeds (Smart et al. 1996, 1998; Webb et al. 2012).

Staffing and funding plant establishment programs can be difficult. Often the only way to accomplish all the steps in the establishment process is to partner with local communities, fishing clubs, lake associations, and schools (Figure 11.3). However, involving partners on plant-establishment programs is not a tough sell (Webb et al. 2012). The public can understand the benefit and eventually can see the product of their work. Fishing clubs often benefit directly through increased catch rates.
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11.4.1 Plant Selection

Various plants have demonstrated potential for establishment in reservoirs (Table 11.1), and many others have been considered with limited or no success (e.g., sago pondweed Stuckenia pectinata, coontail Ceratophyllum demersum, muskgrass Chara spp., three-square bulrush Scirpus americanus, wild blue iris Iris missouriensis, swamp dock Rumex verticillatus). However, this aspect of reservoir habitat management is still in its infancy and relatively little is known about how to establish plants successfully. Perhaps an initial strategy may be to plant a diverse group of plants to explore which one(s) does best in the target reservoir (Webb et al. 2012). Species could be selected based on anticipated environmental conditions. For instance, in a reservoir known to fluctuate in water level, focusing on drought-tolerant or flood-tolerant species may be a sensible initial strategy. Planting aquatic vegetation or wetland species in reservoirs with extreme water-level fluctuations is unlikely to be successful. Established emergent plants can tolerate temporary inundation for weeks, but submersed species tolerate exposure and desiccation for only days or hours.
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11.4.2 Source of Propagules

Although commercial suppliers may be a source of propagules, local production may often be preferred (Smart et al. 1998). Only a limited selection of aquatic plant species is available from commercial sources. Additionally, propagules available commercially are often marketed as seeds, tubers, winter buds, or root crowns but seldom as mature plants. These commercially available propagules can be used to culture plants and produce mature plants for establishment in the target reservoir. Commercial propagules are often available only seasonally, and availability may not be timely for a planting project. Moreover, even though a species may be distributed throughout the USA, genetic variability among plants associated with climatic diversity may require finding local sources (Webb et al. 2012).
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11.4.3 Propagule Production

Occasionally, stands of plants suitable to provide propagules may be available from local wetlands. More  commonly, propagules may need to be produced in controlled environments (Figure 11.4). Propagule production for establishing founder colonies has focused on rooted plants. Culture of rooted aquatic plants depends on providing adequate light, adequate nutrients through sediment, and adequate levels of inorganic carbon via the water, all of which can be controlled under culture conditions. Nonrooted submersed aquatic plants obtain light, nutrients, and carbon via the water, so they are more difficult to culture. For this reason, establishment of nonrooted aquatic plants depends on access to specimens in natural populations. Detailed requirements for developing the infrastructure needed for propagule production are listed by Webb et al. (2012).
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11.4.4 Plant Establishment in Reservoirs

Once enough propagules are available, it is time to transplant them into founder colonies in the reservoir. Founder colonies are reportedly most successful when they are well protected from wind and wave action and are initiated in water <6 ft deep with a gradually sloping bottom. Sites with minimal wave action usually are associated with clearer water, are near the back of coves, and tend to have fine-textured substrate.  Soft  substrate  allows  for deep  rooting of plants (about 6 in). If a protected shore is not available, wave action may be buffered with hay bales or other wave breaks (section 5.8.2). Depth is critical during plant establishment (section 11.4.5), and depth can be affected by water-level fluctuations. Protection of the founder colony from herbivores (e.g., deer, turtles, fishes) is critical. Various exclosures have been designed to keep herbivores out (see examples in Smart and Dick 1999; Webb et al. 2012). Within 1–2 years, founder colonies are expected to be expanding beyond the exclosure, although herbivores may halt or slow down expansion (Figure 11.5).

In general, planting may begin as early as practicable before or during periods of active growth to ensure establishment. Depending on latitude, planting may range from mid- spring to late summer (Table 11.1). In reservoirs that experience spring floods, planting can be delayed until water levels return to normal levels. Mature propagules can be planted over a wider range of time. Establishment of a viable population from mature propagules is possible in late summer, but late planting reduces the length of the growing season and may decrease the likelihood of success.

Table 11.1. Native aquatic plants potentially suitable for introduction into reservoirs (adapted from Webb et al. 2012).

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11.4.5 Multiple Depths Planting

Many reservoirs experience water-level fluctuations. Founder colonies planted at a single depth level may spend much of the year out of water or in water that is too deep and little time at ideal depths. Moreover, the period of ideal depth may not always coincide with the optimum growing period for a particular species. Establishing founder colonies at multiple depths increases the likelihood that plants will be actively growing and producing new propagules throughout the growing season. Webb et al. (2012) suggest that emergent species should be planted in less than 1 ft of water, floating-leaved species at 2 ft, and submersed species at 2–3 ft depth. To address fluctuating water levels (±2 ft), multiple exclosures may be constructed to track the water. In many reservoirs water levels may fall throughout the growing season, and establishing three or more depth tiers of plants is possible. As water levels change, plants exposed to desiccation or in water too deep generally decline but may recover when water levels return to suitable depths. Construction of exclosures often involve wire mesh and steel posts that can become a navigation hazard during high water if not marked or installed in isolated areas. Obtaining appropriate permits from the reservoir controlling authority before installation is a good practice.
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11.4.6 Post-Planting Monitoring

Monitoring the results of plant establishment efforts is critical for long-term evaluation of the benefits (Smart et al. 1996). Without information on the possible causes of failed efforts—or successes—progress is slower. If a few propagules are planted in an exclosure, post-planting monitoring simply can involve counting the number of clumps within the exclosure. As the clumps begin to grow together, visual estimates of the percent cover of the plants within the plot or exclosure can be made. Line transects can estimate density and species composition as colonies expand outside the exclosures. Monitoring may be continued even after establishment is certain to track the species composition in the community, and desirable species that are missing or present in low quantities can be added selectively.
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11.5 Control of Aquatic Plant Growth

Control of aquatic plants can rely on various strategies that often can be used in combination (an integrated management plan). Selection of the best treatment or combination of treatments depends on the species of plant, the extent of the problem, economic considerations, and local environmental conditions. Frequently, integrated management can provide more efficient control for less cost with superior results by matching individual controls to the goals and resource limitations of the individual situation. Major classifications of controls used in an integrated plan are outlined below.
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11.5.1 Biological Control

Biological control involves the introduction of a parasite, predator, or pathogen into the environment to suppress an unwelcomed plant species (Madsen 1997). Biological control operates by reducing the target population to lower, desirable densities suitable to maintaining fish habitat and recreational use of the reservoir. Therefore, the goal of biological control usually is not complete eradication of a plant from a water body. Biological control frequently is considered as one of the most environmentally acceptable goals for managing overabundance of aquatic plants.

Several broad types of biological control approaches can be recognized (Madsen 1997). These include introduction of host-specific organisms from the native range of the target plant, the use of opportunistic native or nonnative pathogens or insects, conservation or augmentation of native herbivores, and the use of general feeders or non-host-specific organisms. An example of the last is the Asian grass carp that is used to control most types of submersed aquatic vegetation (Figure 11.6). Biological control is typically a long-term approach for the suppression of a target plant species. A disadvantage of using biological control alone is that results can be unpredictable: control can take too long, overrun target levels, or produce undesirable side effects. This long-term method of suppression is best suited in low-priority areas, at sites where the use of other control strategies would be cost prohibitive, or where the goal is maintaining a lower level that has already been achieved. Biological control is a potentially effective long-term control practice when used in conjunction with the short-term chemical or mechanical options (sections 11.5.2 and 11.5.3).

A concern regarding the use of grass carp as a biocontrol agent is the potential of escaped fish to reproduce in the wild or feed on aquatic vegetation the manager wants to preserve. The development and aquacultural production of sterile triploid grass carp has provided a solution to the reproduction problem. As to the latter problem, grass carp stocking may not be prudent in open systems that are connected to a stream or river because grass carp are attracted to moving water and will leave the stocked water body. Grass carp stocking rates in closed systems typically range between 2 and 50 fish/ac. There is no “magic number” of grass carp to stock to achieve a specific percentage of submersed weed control because optimum stocking rate is dependent upon the type and quantity of aquatic plants present, water temperature, lake morphometry, and desired speed of control. Grass carp remain illegal in many states, and most other states require permits for use of the fish.

Various introduced and native insects (e.g., beetles, weevils, moths, mites) have been used for the control of alligator weed (Alternanthera philoxeroides), water hyacinth (Eichhornia crassipes), hydrilla, purple loosestrife (Lythrum salicaria), Eurasian watermilfoil (Myriophyllum spicatum), giant salvinia (Salvinia molesta), and water lettuce (Pistia stratiotes) (Newman 2004). The use of insects as biological control agents for aquatic plants has yielded mixed results, which is typical and expected of biocontrol programs. However, a few aquatic plants, including alligator weed and purple loosestrife, have been controlled successfully by insects released as biocontrol agents. Control of other plants—including water hyacinth, hydrilla, Eurasian watermilfoil, and giant salvinia—has been less successful. Multiple factors often play a role in the failure of some biocontrol agents to reach their full potential. Insects can be an effective tool in the manager’s toolbox since host-specific biocontrol agents allow management of populations of undesirable species while leaving nontarget plants unharmed (Newman 2004). A major factor that limits insect utility is that unless a potential control agent is species specific, it cannot be introduced into the USA. Therefore, it is unlikely that a plant control program can rely on biocontrol alone.

Biological control also can involve introduction of desirable native plant species to fill the vacant niche resulting from disturbance due to other control measures. If the native species can preempt recovery or reduce the probability of reintroduction of nuisance species, the temporal benefit of the original control measure can be prolonged and the need for additional control inputs may be minimized.
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11.5.2 Mechanical and Physical Control

Mechanical and physical control practices have been used to control many aquatic plants, especially invasive and exotic species.
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11.5.2.1 Hand pulling

Hand pulling is similar to weeding a garden. The whole plant, including the roots, is removed while leaving any desired accompanying plant species intact. This procedure works best in soft sediment, with shallow rooted species, and in small (discrete) areas. Hand pulling can be a highly selective technique, provided the target species can be identified easily (Kettenring and Adams 2011). The process has to be repeated often to control regrowth. When hand pulling nuisance species the entire root system and all fragments of the plant are pulled; even small root or stem fragments could result in additional growth. Once the bottom substrate is disturbed, suspended sediment often greatly reduces visibility, which results in the need to make multiple passes over the same area. The time required by hand-pulling operations varies widely depending on the degree of infestation. Hand pulling usually is used as a component of invasive species management programs to target new infestations with low plant density (generally <500 stems/ac). Hand pulling is often an important follow-up strategy to an herbicide treatment program to extend the duration of plant control.
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11.5.2.2 Hand cutting

Hand cutting can be used for localized removal of invasive aquatic plants. The removal of small patches of vegetation can be accomplished by cutting with hand tools while wading along the shoreline or floating on a small boat in shallow water. This approach is feasible only in areas where water level allows access, usually less than about 4 ft deep. Various commercial companies have developed power and nonpower hand tools specifically designed to remove submersed aquatic plants. Because many submersed aquatic plants spread by fragmentation, hand cutting may exacerbate the problem, but that depends on the plant. If the plant spreads by fragmentation, hand cutting operations may be appropriate only in lakes where the plant has expanded to most of the littoral zone. Cutting pioneer colonies could accelerate the spread of the plant to noninfested areas.
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11.5.2.3 Hand rakes

Hand rakes of varying sizes and configurations are available for aquatic weed control. Many of these hand rakes are lightweight aluminum with rope tethers and are designed to be thrown out into an area and dragged back onto shore. Some are designed to cut the weeds instead of raking them back to shore. While these may be cost-effective strategies to manage small areas, there is a risk that these rakes will make the problem worse by creating weed fragments that can escape and infest other portions of the reservoir.
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11.5.2.4 Mechanical harvesters

Mechanical harvesters are machines that cut and collect aquatic plants (Figure 11.7). These machines can cut the plants 5–10 ft below the water surface and may cut an area 6–20 ft wide. Most mechanical harvesters are highly maneuverable around docks and boat houses and can operate in as little as 12–18 in of water. The plants are cut and then collected by the harvester, stored within the harvester or accessible barge, and then transferred to an upland site (Madsen 1997). The advantages of this type of weed control are (1) cutting and harvesting immediately opens an area, such as boat lanes; (2) plants are removed during harvesting and do not decompose and  reduce dissolved oxygen in the water column as they do after herbicide application; and (3) the habitat remains intact because most harvesters do not remove submersed plants all the way to the lake bottom, i.e., clipped plants remain rooted in the sediment and regrowth can begin soon after the harvesting operation. However, there are disadvantages (WDFW  2011).  These include (1) the equipment is fairly expensive; (2) harvesting may have to be repeated several times per growing season to maintain control  of nuisanc aquatic plants; (3) mechanical harvesting leaves plant fragments floating in the water, which if not collected may spread the plant to new areas; (4) harvesters may affect nontarget organisms such as insects, amphibians, and fish, removing them with harvested material; (5) cutting plant stems too close to the bottom can result in resuspension of bottom sediment and nutrients; (6) harvesters are not species selective; (7) harvesters cannot be used where abundant timber was left in the reservoir basin at impoundment; and (8) a crew operating a harvester can generally clear <5 ac/d, whereas a crew applying herbicide can cover 10–15 ac/d.
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11.5.2.5 Track hoes and draglines

Track hoes are large shovel machines, and draglines use a large cable system to cast and drag a shovel that collects plants and organic material (Figure 11.8). Track hoes have claw shovels that can reach 25–30 ft over the water body, dig down, and pull plants back to shore. Shore-based track hoes or draglines are best suited for channel maintenance, in areas where plants accumulate, or in locations where plants can be pushed to an established collection point. Barge-mounted track hoes or draglines can be used for transportation to off-shore work sites. In that case, plants are loaded on an attending barge and hauled to a disposal site.
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11.5.2.6 Legalities of collection and transportation

Plant collection and transportation in most states is subject to various state and federal regulations. Various permits may be necessary. The laws and regulations in this regard are complex, subject to frequent change, and vary among states. Some species may be under special legal protection because of their conservation or nuisance status. It usually is prohibited to transport certain noxious plants within a state or across state lines. Some collection sites, such as aquatic preserves or parks, may be off limit. Thus, several types of regulation may need to be considered when transporting plants to disposal sites or when collecting specimens for establishing plant colonies.
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11.5.2.7 Water drawdown

Water drawdown can be an effective aquatic plant management method (Cooke 1980). It is used for control of submersed species, and it is most effective when the drawdown depth exceeds the depth of invasion of the target plant species. In northern areas during the winter, drawdown will result in plant and root freezing for an added degree of control (Beard 1973). Drawdown is typically inexpensive and has effects that last two or more years. Drawdowns can have various other environmental effects and interfere with other functions of the water body (section 7).

Plants that are controlled by drawdowns usually include many submersed species that reproduce primarily through vegetative means, such as root structures and vegetative fragmentation. Some invasive submersed species most commonly targeted by drawdown include Eurasian watermilfoil, fanwort (Cabomba caroliniana), Egeria spp., and coontail. However, opportunistic species like hydrilla may expand rapidly following drawdown. A general rule of thumb is to maintain drawdown conditions for 6–8 weeks to ensure sufficient exposure to freezing and drying conditions (Figure 11.9).
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11.5.3 Chemical Control Practices

The use of herbicides for the control of aquatic plants represents one of the most effective management options available. Herbicide control is often the first step in a long-term integrated control program (Madsen 1997). Federally approved com- pounds for aquatic plant use are summarized in Table 11.2. The cost of testing and registering aquatic herbicides limits the number of available herbicide options.
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11.5.3.1 Herbicide use and classification

There are approximately 300 herbicides registered in the USA, but only around a dozen are registered for use in aquatic systems (Getsinger and Netherland 1997). Herbicides labelled for aquatic use can be classified as either contact or systemic (Table 11.2). Contact herbicides act immediately on the tissues contacted, causing extensive cellular damage at the point of uptake. Typically, these herbicides are faster acting, but they may not have a sustained effect, in many cases not killing root crowns, roots, or rhizomes. In contrast, systemic herbicides are translocated throughout the plant. They are slower acting but often result in mortality of the entire plant.

Table 11.2. Characteristics of U.S. Environmental Protection Agency approved aquatic herbicides including trade names, formulation, and whether they target submersed, floating, or emersed plants. Listed in parentheses is whether the herbicide is contact (acts immediately on the tissues contacted) or systemic (translocated throughout the plant).

In treating submersed species, application is made directly to the water column as concentrated liquids, granules, or pellets, and the plants take up the herbicide from the water. The applicator needs to know the water exchange rate to determine the appropriate exposure time and concentration of the herbicide required to control a specific target plant. This value may be different for each target species. Species with significant above-water vegetative surfaces, such as floating and emergent species, can be treated with direct application to the surface of the actively growing plant (Figure 11.10). For these species, care is taken to avoid application if rain events are likely.

Instructions for the use and application of herbicides change often. Whether an herbicide is appropriate for a water body or aquatic system with a particular water use is specified on the product label. Always follow the instructions on the label and check with the appropriate regulatory agencies in your state before applying herbicides to any body of water.
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11.5.3.2 Selectivity

Herbicide activity can be characterized as species selective or nonselective (Getsinger and Netherland 1997). Nonselective or broad-spectrum herbicides control all or most vegetation because they affect physiological processes common to all plant species. Because nonselective herbicides can kill all vegetation they contact and not just the problem species, care is taken that they do not affect desirable plants. Selective herbicides will control only those groups of plants that carry the biological pathways targeted by the chemical active ingredient.
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11.5.3.3 Control of specific plants

A wealth of information is available online about invasive species in general, common nuisance species in particular, and relevant species-specific treatments. Because these are changing often, details are not considered here. The following websites are excellent reference sources and updated often:

The University of Florida Center for Aquatic and Invasive Plants http://plants.ifas.ufl.edu/

U.S. Department of Agriculture Natural Resources Conservation Service, Plants Data- base http://www.plants.usda.gov/

U.S. Army Corps of Engineers, Aquatic Plant Management Information System http://el.erdc.usace.army.mil/apis/

Texas AgriLife Extension Service Aquaplant: A Pond Manager Diagnostics Tool http://aquaplant.tamu.edu/
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11.5.4 Cultural Control Practices

Cultural control techniques focus on a large array of social methods used to prevent or reduce the entry or spread of unwanted aquatic plant species. Cultural control practices can be an essential component of long-term management and prevention of aquatic plant infestations.
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11.5.4.1 Prevention

Prevention is one of the best and most cost-effective methods to avoid aquatic plant infestations (Figure 11.11). A commitment of volunteer time to a plant control program can save thousands of dollars in invasive plant management costs. Volunteer boat cleaning, inspections, and temporary quarantine during transfer of watercraft are all components of prevention programs. However, this type of program does require management, education, and planning. Because nutrients and sediment influence the presence and growth of macrophytes, curtailing their flow into the reservoir is important. Preventive maintenance or actions that can be taken include curtailing fertilizer use; using a phosphorus-free fertilizer on established lawns; developing landscaping practices that do not require nutrients and instead will trap nutrients running into the reservoir; maintaining septic tank systems to prevent failures and supporting laws aimed at preventing construction of septic tanks in unsuitable soil types; and supporting the adoption of ordinances designed to minimize surface water runoff and unnecessary land clearing during construction.

Boat ramp monitoring programs are used to inspect boats and trailers for the presence of invasive species. These are largely volunteer or summer intern positions that try to staff boat ramps during peak-use periods. Inspections can be either mandatory or voluntary and usually only take a matter of minutes. The interaction with boat ramp monitors also provides an opportunity to distribute educational materials.
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11.5.4.2 Education

Education is a key component of prevention. Educating reservoir users and the general public about the threat of invasive species is necessary to prevent new infestations and to sustain effective aquatic plant management programs. Education involves creating public awareness of the problem and familiarizing people with possible solutions.

Education facilitates involvement of both volunteer labor and other resources to accomplish a management goal. Many activities can be used for education, including workshops, public meetings, press conferences, news releases, posters and flyers, popular articles, postings at boat ramps, videos for interest groups, development of publicized web sites, and involvement of recreation associations, fish and wildlife groups, and social media. Well-educated citizens and technically informed agency biologists are essential components in the successful control of invasive aquatic plants. Educational efforts may focus on preventing the spread to new water bodies by educating the nursery and aquarium trade, recreationists and boaters, the general public, and policy makers. A lake association or friends of reservoir chapter can help with these activities (section 13.5).
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11.6 Promotion of Terrestrial Plants on Barren Shorelines

Barren shorelines in reservoirs are caused by water-level fluctuations and their negative effect on flood-intolerant plants (section 7). In contrast to other engineered environments, attempts to establish and improve the vegetation of bare reservoir shores have been few (Allen 1988; Fraisse et al. 1997). Gill and Bradshaw (1971) proposed three explanations to account for those reservoir shorelines that are devoid of vegetation: (1) the environment is so extreme that plants are incapable of colonizing or growing; (2) the environment in the margins is not extreme, but suitable plants for colonization do not grow nearby; and (3) the environment in the margins is sufficiently extreme to prevent natural colonization, but not vegetative growth—if plants were introduced by artificial means, they would flourish. The first explanation is plausible if the extreme environment is caused by water levels that fluctuate relatively quickly or drop too late in the growing season so that time available for establishment is minimal. If so, artificial plant establishment could mitigate this deficiency. The second explanation is unlikely because plants generally have high dispersal ability. To be sure, well-vegetated riparian zones may be encouraged above normal (summer) pool elevation. These can act as “source” sites for colonization of the drawdown area. The third explanation suggests that if suitable seeds are absent from the substrate, or are unable to germinate, then the introduction of propagules may be needed to attain basic vegetation cover (Brock and Britton 1995). Indeed, it has been found that the use of appropriate species and management techniques can create plant communities that will survive and benefit from flooding and exposure (Allen and Klimas 1986; Allen 1988).
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11.6.1 Well-Vegetated Riparian Zones

Properly managed riparian zones are advocated to filter potential pollutants from inflowing runoff, to provide a source of shade and woody debris for the littoral zone, and to maintain desirable aesthetics (section 8). However, a riparian zone also can be thought of as a source of seeds for plant colonization of the fluctuation zone of a reservoir. To be effective as such, the riparian zone needs to include a plant community consisting of upland and wetland species capable of colonizing the fluctuation zone at various times of the year, depending on timing of drawdown. This flexibility can be achieved by maintaining a diverse natural plant community including a mix of aquatic grasses, sedges, and rushes along with upland plants growing on shore. Riparian zone management is discussed in section 8.
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11.6.2 Seeding

Seeding of herbaceous terrestrial plants in dewatered fluctuation zones can succeed if done during the growing season, although historically seeding has had mixed success (Figure 11.12). Candidate plant species for seeding mudflats in regulated zone of reservoirs are suggested in Table 11.3. Hulsey (1959) successfully planted rye in Arkansas reservoirs in late September. In Kansas reservoirs, Groen and Schroeder (1978) planted rye (30–60 lb/ac), ryegrass (10 lb/ac), and wheat (30–60 lb/ac) during September or October. In drawdowns before August, Japanese millet and hybrid sudan–sorghum were planted in Kansas and Arkansas, leading to lush stands (Groen and Schroeder 1978). However, summer drought conditions can lead to poor survival (Ploskey 1986). In some situations it may be possible to raise water level slightly to “irrigate” the seeded vegetation, but this has not been tried. Strange et al. (1982) planted rye, fescue (Festuca spp.), a sudan–sudan hybrid, and a sudan–sorghum hybrid (45 lb/ac) from July to September on the exposed mudflats of Lake Nottely, Georgia. Grasses grew poorly in unfertilized sites but did well when fertilized. The numbers of aquatic insects, small sunfish, and age-0 black basses were higher in seeded areas. Ratcliff et al. (2009) planted barley at Shasta Lake, California, and observed that juvenile black bass abundance over 50 times higher in planted grass.

Various site factors are considered in planning a shoreline revegetation effort (Allen and Klimas 1986). These include water-level fluctuation range and time of year; bank morphometry (i.e., steepness and shape); extent of wave action; animal depredation potential; and soil texture, fertility, and moisture status. Success rates are likely to be highest on sites that are gently sloping (i.e., bank slopes not greater than 1:3 vertical to horizontal), are protected from extreme wave action, have soils conducive to plant growth, and do not support high populations of potentially destructive animals, e.g., beavers, muskrats, and cattle. Sites with adverse characteristics such as steep or vertical banks can be vegetated but will require more effort and expense. Soils consisting predominantly of shrinking and swelling clays or those having high concentrations of sodium salts are less likely to produce plants. Soil analyses can identify such prohibitive characteristics and aid in choosing sites to be revegetated and target plant species, as well as determine if soil amendments will be needed.
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11.6.3 Timing

As a general rule seeding is conducted when favorable soil-moisture and temperature conditions are going to occur. Often, it is best to seed or plant in the fall just after water levels drop so the planting substrate is still moist. Nevertheless, if reservoirs are at their lowest level during December or January and rise very slowly during the spring, seeding or planting could occur during winter to early spring, depending on rainfall availability, temperature conditions, and plant species. Some grass and herbaceous species can be seeded or transplanted in either the spring or the fall, while others establish better in a particular season.
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11.6.4 Seeding Methods

The methods of seeding are determined by location, size, and topography of the reservoir shoreline; time of drawdown; water level; seed mixture; and soil conditions. If the revegetation site will be subjected to fluctuating water levels or wave action soon after planting, seeding is probably not the best plant establishment alternative because the seeds are likely to wash out. If reservoir water levels are lowered long enough for seeds to germinate and plants to grow, seeding will be the most cost-effective means of establishing plants, particularly grasses and forbs. Fowler and Maddox (1974) and Fowler and Hammer (1976) were successful in seeding mudflats in Tennessee reservoirs by means of various techniques, some of which are described below.
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11.6.4.1 Broadcasting

The most common method of seeding on large areas is to disperse seed from a tractor-mounted or all-terrain vehicle (ATV)-mounted broadcast seeder. Broadcasting by hand with a knapsack seeder usually is restricted to small areas or inaccessible sites such as steep slopes. Broadcasting by hand is labor intensive and used only when no other method is applicable. Because of the relatively harsh growing conditions on reservoir shorelines, three to five times the normally recommended amounts of seed may need to be mixed thoroughly with fertilizer and sawdust or sand and broadcasted over the site. The sawdust or sand serves as an indicator of areas already seeded and promotes a more even distribution of seeds. Broadcast seeding is rapid and easy but is typically not recommended for large or fluffy seeds that may plug the equipment, blow away, or be lost to scavenging animals.
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11.6.4.2 Drill seeding and cultipacking

Drill seeding (Figure 11.13) and cultipacking (Figure 11.12) are generally preferred over broadcast seeding. Both of these methods will place seeds in the soil at the desired depth and cover them with soil for germination. Tractors or ATV-mounted seeders may be used. These seeders often have one or several seed boxes designed to seed various seed sizes and mixtures (small and dense, light and fluffy, or medium-heavy seeds) with fertilizer at the time of seeding.

Drills have coulters that will lay open the surface soil for seed placement, leading to better seed–soil contact. Drill seeding has been successful on some reservoirs and can be done cost effectively if terrain and soil conditions permit. The South Dakota Game, Fish, and Parks successfully drill-seeded reed canary grass (Phalaris arundinacea) on a shoreline of Lake Oahe reservoir. Reed canary grass provides spawning substrate for northern pike.

Cultipackers cover the seed with a minimum amount of soil to ensure proper seed-to-soil contact. It resembles a large rolling pin with evenly spaced ridges and dimples. The cultipacker’s primary functions are to break up clods, remove excess air spaces from loose soil and smooth the soil’s surface. This method consists of heavy-duty, smooth, spoke or crowfoot rollers that provide clod-breaking and smoothing capabilities. As with any tillage, it is important not to overwork the soil or work it when it is too wet.

A diversity of equipment is available to spread and bury seeds with ATVs. Up-to-date information can be obtained at web sites that specialize in food plot seeding implements.
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11.6.4.3 Hydroseeding

Hydroseeding involves spraying a slurry of seed, fertilizer, mulch, and water onto a site (Figure 11.14). It is commonly used for seeding steep road banks or the uneven terrain of surface-mined lands. It may be used to vegetate reservoir shorelines by mounting the equipment on a barge that can be towed to otherwise inaccessible sites. Fowler and Hammer (1976) described modified hydroseeding equipment, the aquaseeder, which was developed for the Tennessee Valley Authority and was tested successfully along reservoir regulated zones. Hydroseeding has the advantages of using a one-step application of seeding materials and the ability to seed large areas of rough terrain. Disadvantages are that it can damage seeds, and broad mudflats may be inaccessible to floating hydroseeding equipment. Because of potential soil erosion associated with steeply sloping reservoir shorelines, mulching over the seeds is often required to protect the surface soil. However, mulching is used only if water levels will remain down until the plants have reached a desired size.
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11.6.4.4 Aerial Seeding

Seeding from aircraft is a specialized technique and can be quite expensive unless it is applied to large areas (i.e., >100 ac). It is often used where site features prevent conventional methods from being used. In 1973 and 1974, the Tennessee Valley Authority successfully used this technique with a helicopter and a hopper-spreader unit to vegetate >1,000 ac of mudflat on an experimental basis. The helicopter operated 20 ft above the ground over a 30-ft swath at the speed of 30 mph and spread 20 lb/ac of annual ryegrass. A possible disadvantage of using helicopters for aerial seeding on reservoirs, particularly where drawdowns are erratic, is the difficulty of scheduling the service (Fowler and Hammer 1976). Also, steep shorelines may be difficult to seed with this method because of the inability to achieve a uniform spread and obtain good seed–soil contact.
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11.6.5 Transplanting

In contrast to seeding, transplanting uses one or more of several kinds of planting stocks, including bare-root seedlings, rooted or uprooted cuttings, balled-and-burlapped plants, containerized plants, sprigs, plugs, rhizomes, and tubers. Transplanting is generally more effective than other establishment techniques because root system development and height growth are maximized during the growing season prior to inundation of the site. Nevertheless, transplanting requires substantially more labor than seeding and may be impractical in large areas. Moreover, plants are seldom available from commercial growers and have to be either removed from wetlands or grown in an in-house nursery.
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11.6.6 Grasses and Other Herbaceous Plants

This group of potential transplants may include wetland species of the genera Carex, Cyperus, Eleocharis, Juncus, Panicum, Polygonum, Phragmites, Sagittaria, Scirpus, Spartina, and Typha. There are four forms of propagule types commonly used to establish grasses and other herbaceous plants as transplants on reservoir shorelines.
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11.6.6.1 Sprigs

This propagule is the entire plant dug and removed from its natural habitat and transplanted to the new site. The term “sprig” generally refers to smaller transplants that are obtained by breaking multistemmed plants into smaller clumps containing one to five stems. It is best to leave soil on transplant roots when they are dug to minimize root loss and disturbance. Plants dug during the dormant season usually suffer less from stress and shock than those dug in the late spring and summer.
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11.6.6.2 Rootstocks and plugs

Rootstocks consist of the root system of a plant, including that portion of stem normally growing below ground. The propagule may be divided into sections or clumps for planting; new growth will generate from the old root systems. Plugs are obtained by extracting rootstocks with some type of coring device. This approach was applied to planting marsh in western New York; cores of wetland soil were transplanted in a grid pattern on 3-ft centers and subsequently flooded (Allen and Klimas 1986). The cores contained various types of propagules that were present in the source wetland, including rootstocks, rhizomes, seeds, and whole plants. Plugs can be carried in plastic bags to a shoreline to be vegetated and planted in or out of water. Planting in water, however, is very time consuming and more costly. Using plugs and the coring method described would have its greatest utility in reservoir areas shallowly covered by water, such as some mudflats and shallow-sloped shorelines.
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11.6.6.3 Rhizomes and tubers

Rhizomes are similar to rootstocks but refer to underground stems that often grow horizontally. The rhizomes are dug and divided into sections, taking care to keep at least one viable growth point (node) on each to ensure new growth. Tubers are large, fleshy underground stems often associated with rhizomes. They are usually available to be dug near the end of the growing season.
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11.6.7 Trees and Shrubs

This group of potential transplants may include wetland species of the genera Salix, Cornus, Morus, Nyssa, Populus, and Taxodium. Four propagule types may be used to establish trees and shrubs in the drawdown zone of reservoir shores: bare-root seedlings, cuttings, and balled-and-burlapped and containerized plants. These four types exhibit various advantages and disadvantages.
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11.6.7.1 Bare-root seedlings

Bare-root seedlings are young plants with exposed root systems that are transplanted from nursery beds or from natural stands to the planting site. Seedlings of trees and shrubs are usually hand planted, using either a mattock or planting bar (dibble) for preparing a hole. Bare-root transplants are successful for many tree and shrub species, but because site conditions can be restrictive, survival will probably be higher with container-grown stock (Allen and Klimas 1986). The advantages of using bare-root stock are that seedlings are easier to handle, are less costly, and are easier to plant. These characteristics make bare-root materials appropriate for planting larger areas.
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11.6.7.2 Cuttings

Cuttings are sections of the shoots of a plant and include nodes in the section cut. Cuttings may be unrooted or rooted. To obtain rooted cuttings, roots have to develop in an appropriate rooting soil, possibly treated with a root stimulator. If planted as unrooted cuttings, the cut section can be placed in the substrate at the planting site. The size of cuttings may vary from thin slips (<0.5-in diameter) to large poles (4-in diameter, 10 ft long) (Allen and Klimas 1986). When cuttings are planted, they need to extend deep enough into the soil to be firm and relatively difficult to pull out; only 1–2 in may be left above ground to prevent moisture loss, with any excess pruned off. Cuttings may be pushed directly into the soft soils of recently dewatered areas (Gray and Leiser 1982). Not all trees and shrubs will reproduce from cuttings; only those that sprout readily from the stem are likely to grow. Examples of woody species that readily sprout from the stem include all willows (Salix spp.), some poplars (Populus spp.), river birch (Betula nigra), swamp privet (Forestiera acuminata), and some alders (Alnus spp.). Use of unrooted cuttings could be an economic method of plant establishment, so some pilot testing plots may be considered.
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11.6.7.3 Balled-and-burlapped propagules

Propagules that are balled-and-burlapped refer to large trees and shrubs >5–7 ft tall that have been nursery grown with balled-and-burlapped root systems. These propagule types are normally too expensive for most shoreline revegetation projects, except in recreation areas that are subject to periodic inundation and for which higher planting costs can be justified.
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11.6.7.4 Containerized propagules

Containerized tree and shrub propagules are those that have been grown in pots or similar containers. Plants grown in gallon-sized or larger containers are often available for tree and shrub species used in regular commercial landscaping but are limited in variety. Consequently, they may not be best for use on reservoir shorelines that are periodically inundated, unless a nursery has been contracted to grow flood-tolerant species. Survival frequently is reduced because of limited root systems in relation to size of the tops of the plants (Allen and Klimas 1986). The main advantage of containerized plants is that they have developed root systems and stems that are ready to grow when they are placed into the ground. However, containerized plants cost considerably more than other propagule types. Therefore, they are often reserved for high-priority recreation sites or other such sites requiring greater assurance of success.

At Lake Fork, Texas, containerized buttonbush (Cephalanthus occidentalis) was introduced successfully on the exposed littoral zone during a prolonged drought (R. Ott, Texas Parks and Wildlife Department, personal communication). These specimens persisted when the reservoir level recovered. However, similar introduction of additional containerized specimens in the same area following water-level recovery was unsuccessful because wave action uprooted the specimens before establishment could occur.
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11.6.7.5 Spacing

Spacing of plantings generally ranges from 2 to 15 ft centers. Nevertheless, spacing is influenced by the project goal. Spacing for aesthetic improvement of a project area may be different than when the goal is to improve fish habitat. Other factors that may be considered in selecting the plant spacing includes growth patterns, survival rate, time of planting, and propagule type.
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