Gather Background Information
The first step in an IVM program is to gather information on the life cycle and habits of the noxious weed.
The genus Spartina, commonly known as cordgrass, occurs mostly in wetlands and estuaries. Smooth cordgrass, Spartina alterniflora, is a perennial saltmarsh grass that grows in intertidal mudflats. The stems are stout and the rhizomes form an extensive root system that is roughly 5 times larger than its aboveground biomass. Flowers are smooth, lacking hairs, and leaf blades grow up to 18 inches long (Mobberly 1956; Partridge 1987; Bishop 1998).
Once established, smooth cordgrass spreads vegetatively, forming ring-shaped clumps of individual clones. These clones are tall and conspicuous against open mudflats. New stems grow along the outer edge of the ring, gradually increasing its diameter with each growing season, while old, dying vegetation can be found in the middle. As clones spread, they grow into each other, forming a dense monospecific meadow and outcompeting native plants. The success of S. alterniflora can be attributed to its high rate of spread, its tall, dense, canopy that can shade out other plants, and its ability to colonize low intertidal regions (Daehler and Strong 1994; EIS 1993; Callaway and Josselyn 1989).
The geologically young Pacific Coast estuaries have unique open mudflats devoid of vegetation, and are highly vulnerable to Spartina invasion. Spartina can alter ecological processes that govern wetland ecosystem function. Infestations can alter the physical aspect, structure, and spatial configuration of wetlands through dense growth and sediment accumulation. Although the amount of sediment accumulation is variable from site to site, Spartina's dense root and stems effectively trap sediment at higher rates than normal, altering water movement. Large Spartina infestations can turn a wetland into a Spartina meadow. In addition, its ability to colonize low intertidal areas can cause restricted water flow, which clogs navigation and flood-control channels (Smith 1998; Josselyn 1993; Daehler and Strong 1996 a, b).
S. alterniflora's ability to colonize low intertidal mudflats threatens the habitats of migratory and resident waterbirds that require open mudflats for foraging. Spartina also affects fisheries because fish utilize estuaries as nursing grounds or foraging sites.Spartina can also overtake intertidal sea grass beds that provide important habitat for juvenile fish. In Washington, the Pacific oyster industry is concerned about Spartina’s encroachment upon open mudflats, which can decrease the available area for oyster cultivation and reduce oyster growth by decreasing the amount of nutrients reaching the oyster beds (EIS 1993).
Smooth cordgrass, S. alterniflora, is native to the Gulf coasts and the eastern seaboard of the United States, and has been introduced on the Pacific Coast along Washington, Oregon, and California. It has also been introduced worldwide for erosion control efforts in countries such as Great Britain, France, The Netherlands, New Zealand, and China (Partridge 1987; Spicher and Josselyn 1985).
Spartina spreads both by root fragments and seeds, which are both buoyant and dispersed by storms and water currents. Seeds can also be dispersed by wind and waterbirds. Although flowering and seed germination times vary by climate and geographic range, flowers usually appear in late July through August and set seed in late September through October. Spartina seed viability is low and germination is greatly reduced after 1 year.
In cold climates, Spartina dies back in the winter, sending up new shoots each spring; however, in more temperate areas some plants can stay green year round (Callaway and Josselyn 1992, 1993; EIS 1993; Daehler 1996; Smith 1998; Sayce 1988; Kovacs 1998).
Spartina is difficult to control because of its extensive root network. It also spreads rapidly in areas that are hard to traverse. Since Spartina grows in the intertidal zone, the substrates may be soft and muddy.
Glyphosate is the only chemical registered for aquatic use in the U.S. and its use is problematic. Glyphosate readily binds to sediment particles, which reduces the translocation of chemical down to the roots. Daily inundation by tides covers plants with mud and dirt, reducing herbicide effectiveness. In addition, application must be timed with tidal fluctuations to allow glyphosate to dry roughly 6 hours. Decreased drying time gives decreased efficiency.
Some questions, such as those below, can only be answered on site.
Set Realistic Goals
for Your IVM Program
The answers to the following questions can help you set realistic objectives and goals.
Prevention - reducing or eliminating the conditions that allow the weed to spread or gain a foothold. This strategy, which includes good land management, enhancement of desirable vegetation, and public education, should always be employed. Spartina establishes on sites that are devoid of vegetation and can outcompete native plants; therefore, planting competitive vegetation cover may not be feasible for this weed.
Containment - keeping an established weed population in check so that the area infested by the weed does not increase. This strategy can be employed against newly-invading weeds or slowly spreading well-established species. It is especially useful when time and money are in short supply or when the infestation is very large.
Reduction - reducing the area covered by a weed, or reducing the dominance of that weed. This strategy can also be used against new or established weeds, but it requires more resources and more time than containment.
The "Bradley Method" (see Appendix 2), developed in Australia, is a simple yet innovative strategy for natural areas that combines containment and reduction.
Eradication - completely eliminating the weed from the management area. This strategy usually consumes the greatest amount of time and resources and is applicable mainly to newly-invading weeds that are confined to a limited number of small areas.
Establish Monitoring Programs
When planning a monitoring program, keep in mind the context of your target weed: is it invading or has it already invaded?
Locate and record Spartina infestations on a map. (Chapter 2 of the University of Northern Iowa IVRM Technical Manual contains a detailed discussion on how to map and inventory vegetation - see Bibliography). Note particularly sensitive areas on the map, such as critical habitat for threatened or endangered species, agricultural production areas, or areas subject to frequent disturbance and thus prone to invasion. Update maps at regular intervals.
Focus monitoring efforts on sites where problems are most likely to occur (see Distribution). Encourage public sighting and reporting through an education or incentive program (see Educate Vegetation Management Personnel and the Public).
Prioritize the sites you will work on. Make a realistic assessment of your weed management resources, keeping in mind the goals of your project and the cost of a follow-up program after any treatments. Without follow-up, your control efforts will be wasted. It is better to thoroughly control a weed at one or two sites than to use up resources to incompletely control the weed at many sites. If the weed is very widespread, try to determine where it poses the most serious economic, social, or environmental problem and concentrate on those areas.
Plan monitoring and treatment efforts to coincide with critical life stages of the weed. To use your resources efficiently, try to include monitoring with other planned activities in the area.
Maintain records of your monitoring activities. Creating standardized forms will make data collection easier and help remind you to gather all the information you need. Forms work best if they include labeled blanks for all pertinent information and allow the user to check or circle rather than having to write words or numbers (See Appendix 3 for some examples of forms).
Include information such as the name(s) of the person(s) collecting the data, the location, and date of monitoring; a qualitative description of the vegetation, such as the names of the plants or types of plants (native vegetation, annual/perennial weeds, trees, etc.) and stage of growth (germinating, flowering, setting seed, etc.); a quantitative description, such as percent cover, plant density, size of the patch, or if possible, the number of plants.
Note special conditions such as unusual weather events and record treatment history, including information on treatment applications (who, when, where, how, cost, difficulties, and successes). This will allow you to evaluate and fine-tune treatments.
Set Treatment Thresholds
Setting treatment thresholds includes prioritizing and balancing treatments with resources. Weeds are treated when populations increase beyond a predetermined level. This level will largely depend on the characteristics of the site and weed. In some cases the level may be no weeds at all, and in other cases the number of weeds you can tolerate may be much greater.
What is the size of the weed population? The opportunity for control is related to the infested area. Small patches can be more easily controlled than large infestations.
What is the level of the threat? Is the Spartina population changing? Is it in an area where soils are frequently disturbed? Does it threaten agriculture, pastures, or rangeland? Is it encroaching on critical habitat for a rare, threatened, or endangered species? Is it displacing the best examples of native communities?
What resources are available? Do you have the resources required for carrying out your goal?
With the advent of herbicides, prevention as a weed management technique has often been neglected; however, it is a practical, cost-effective, and extremely important part of noxious weed control.
General Weed Prevention Measures
Apply Management Methods
No individual method will control Spartina in a single treatment; diligence and persistence will be required over a number of years to subdue this weed. The treatment methods described in this section will help you to design an integrated program that will suit the circumstances of your particular situation.
Spartina poses challenges to implementing control methods because of its location in soft soils. Special shoes and equipment can make wetlands and marshy areas more accessible. "Mudluks," tire innertubes attached to the bottom of a foot support, increase the contact surface area and facilitate walking on soft mud. Similarly, mudshoes, commonly worn by oyster farmers, are platter-shaped snowshoes with small innertubes on the bottom and straps on the top. A walkway of planks or plywood can also be laid to the treatment areas and boats, airboats, and hovercraft can facilitate movement in the mudflats. Airboats, powered by large air propellers, can negotiate the shallow waters of intertidal areas. Another useful vehicle that makes it possible to reach muddy Spartina sites is the hovercraft, a boat that rides on a cushion of air and "hovers" above the ground (EIS 1993; Bishop 1998; Sayce 1998).
Biological control does not aim to eradicate weeds, but to keep them at low, manageable levels. After their introduction, biocontrol agents can take 5 to 10 years to become established and increase to numbers large enough to cause damage. Once established, effective biological controls provide an inexpensive, long-term, and non-toxic means to control weed populations. Although no beneficial insects have been released for Spartina, greenhouse studies of biological control agents are being conducted in Washington state.
In Willipa Bay, Washington, S. alterniflora clones have been growing in the absence of herbivores for roughly 100 years and are susceptible to insect attack. It is thought that these plants have invested more energy in plant growth and subsequently lost resistance to herbivory (Daehler and Strong 1997a).
Prokelisia marginata, a plant hopper, can severely damage or kill Willipa Bay plants. Tests continue to look at the plant hopper’s potential as a host-specific bio-control agent (Daehler and Strong 1994, 1995, 1997a).
Physical controls for Spartina consist of removing plants by hand, with machinery, or by covering. Integrative management programs to control Spartina on the West Coast are relatively new and studies continue to fine-tune methods for site-specific management.
Diking, Mowing, and Covering
In Humbolt Bay, California, managers took quick action to eradicate a S. alterniflora infestation. Since its eradication, S.alterniflora has not re-colonized the area. The California Department of Fish and Game used a combination of diking to reduce tidal flow and covering to smother the clone. A series of wire gabion baskets, commonly used for streambank erosion control, were lined with plastic and filled with rocks and sand. Two to four baskets, each basket roughly 3 ft tall, were stacked around the Spartina clone, to restrict and stagnate the water around the clone. Although the barricade did not completely stop incoming water, it greatly muted tidal action. In addition, the heavy gabion baskets seemed to prevent roots from spreading to outside areas. The clone was also mowed to the ground, and covered with heavy plastic for 3 years.
The drawbacks to these techniques are the large amount of labor required and its high costs. In addition, diking may not be appropriate or feasible in many areas (Kovacs 1998).
In IVM programs, herbicides are considered transition tools that enable the manager to suppress weeds and replace them with desirable, competitive vegetation. Thus, it is important to select the least-toxic, low-residual herbicide that is effective against the target weed, and to apply them in a judicious manner.
Wiping herbicide onto plants both cleans the dirt off plants and applies herbicide, but is labor intensive. Although crushing or bruising Spartina by foot stomping or driving over plants with vehicles is not effective alone, it can increase Spartina's susceptibility to chemical control. However, if stems are pushed too deep into the mud, it will be shielded from herbicide spray (Doody 1982; Sayce 1988).
In a study by Killbride et al. (1995), ground rather than aerial treatments obtained greater control. Ground treatments also increases herbicide contact supposedly by the dual action of brushing on higher concentrations of chemical and by the cleaning action of the wiper. Ground, compared to aerial applications decrease the amount of herbicide drift.
Applying herbicide to plants before seeds are produced and when the weed is most susceptible are crucial to the effectiveness of the treatment. Herbicide must be applied during an outgoing tide for maximum drying time. Decreased drying time usually results in decreased efficiency.
Vegetation Management Personnel
and the Public
Evaluate the Vegetation Management Program
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