San Francisco Estuary Invasive Spartina Project
Control Program
Treatment Methods

Treatment methods used by the Control Program include a range of manual, mechanical, and chemical methods. Some of these methods are aimed at killing target cordgrass populations, while some are “support techniques,” which facilitate implementation of a removal method or provide temporary control pending a more permanent solution. Each of these control methods is presented in the two following tables, with treatment types divided between mechanical and chemical methods. Detailed descriptions follow the tables, and can be quickly accessed by clicking on the respective column headings.

See chemical methods.

Table 1. Summary of Mechanical Spartina Treatment Methods

Hand-pulling and
Manual Excavation

Covering/ Blanketing

Pruning, Mowing & Burning

Mechanical Excavation & Dredging

Appropriate Setting

Seedlings, particularly in newly infested areas. Appropriate for small clumps and isolated clones, or sparse infestations.

Small to medium size clones. Larger stands are not easily covered due to the labor-intensive nature of transporting and installing the fabric, and high cost.

Small to medium area. To reduce biomass and facilitate other methods, to stop seed production and other infestation expansion, or prevent cross-pollination. Use repeatedly to stress and kill plants.

Large individual clones >25 feet in diameter or clusters of clones in the mid to lower tidal zone that can be accessed by floating dredge, or by excavator in the upper marsh.

Removal Technique
Removal of plant and below ground material up to 4 feet deep.

Covering blocks light from reaching the plants and interrupts photosynthesis.

Mowing- cut plant at, near, or just below the soil surface for best results; Chemical mowing- use weak concentration to stop seed set and preserve standing biomass for clapper rail refugia
Burning- use handtorch to burn seed head, or controlled burn to clear standing necromass to expose seedlings; Pruning- clip seed heads.

Cutterhead dredge (or similar) on floating barge or excavator removes entire plant and root mass to a depth of 1 foot, and disposes in upland.

Equipment Requirements
Shovels, trowels, bags, wheelbarrows, handcarts, sleds, trucks for transport of removed material.

Geo-textile fabric or black plastic, grommets, stakes.

Clippers, weedeaters, small mechanical cutters, handtorches, helicopter with boom for chemical mow.

Dredge or excavator, trucks to remove material (if not slurried and piped to destination)

Workforce Requirements
Depends on the age and density of the population. An approximate 10-person workforce would be required to pull or dig out a low-density seedling area of about 0.25-acre in an 8-hour day.

Approximately 2-5 persons would be required to place covers over treatment areas, depending on the size of the area. Requires periodic monitoring for tears or movement of covers.

Varies depending on method (and height and density of vegetation). Approximately 2-3 persons required to treat a 0.25-acre area with weedeaters over 8 hours.

One operator per vehicle, and 1-2 persons needed on site during operations.

This method can take place during any season, but is most frequently done in the spring. 1-2 visits per location per year are needed to prevent reestablishment or resprout.

Placing covers early in the growing season would eliminate the need for mowing. Covers must remain in place for two growing seasons to kill plants.

Mowing can be done during growing season. Seed heads form in summer and fall. Eradication by mowing alone would require up to 4-6 treatments annually, for a minimum of 2 years. Burning to expose new growth would be conducted in spring.

Any time of year.

Depends on the diligence of the work crew. Any portion of rhizome left behind can potentially sprout and re-establish the clone. Complete removal results in eradication.

Covering has been successful in the S.F.   Estuary on small patches up to 36 feet in diameter. Failure results from improper installation and/or maintenance. Improperly sealed seams (or lack of sufficient overlap) allow plants to grow through or around the covers. Wind or tidal action may dislodge covers. Sediment may accumulate on the covering.

Results of field tests are variable, and dependent on the frequency and the start date. Repeated application eventually weakens rhizomes and reduces energy reserves. One application often invigorates a plant. Therefore, multiple treatments are necessary.

Large-scale demonstration work in Washington indicates a high level of efficacy.

See mechanical methods.

Table 2. Summary of Chemical Spartina Treatment Methods

Herbicide, Ground or Boat Application

Herbicide, Aerial Helicopter Application

Appropriate Setting
Small, medium, and large individual clones and meadows. Application of herbicide may be used in conjunction with seed head clipping and mowing; must allow sufficient regrowth after mowing to absorb herbicide.

Large, heavily infested areas, meadows, or difficult to access sites. According to ISP’s PEIS/R, aerial treatments must be greater than 0.25 mile from a sensitive receptor.

Removal technique
Imazapyr and/or glyphosate herbicide is combined with a surfactant & colorant and is sprayed, wiped, or painted on foliage, or applied as a paste on cut stems.

Imazapyr/surfactant mix applied by spray apparatus attached to a helicopter consisting of a boom with multiple nozzles for broadcast delivery, or a spray ball for spot treatment.

Equipment Requirements
Imazapyr or glyphosate herbicide, surfactants, colorants, backpacks, spray truck, shallow-bottom boat, airboat, tracked amphibious vehicle, hovercraft.

Imazapyr herbicide, surfactants, colorants, helicopter with boom or spray ball.

Workforce Requirements
1-2 persons needed for small infestations. Backpack crews in heavily infested areas with difficult access would range from 2-6 persons. Typical crews for large infestations would include 2-3 persons per ground application vehicle, or 1-3 persons per boat with support from 1-3 trucks.

Pilot and a ground crew of approximately 2-4 persons.

Mid-summer through early fall

Mid- summer through early fall.

The length of time from application to high tide (i.e. dry time), wind and weather conditions, application method, and timing of application in the plant's life cycle are all important factors. Efficacy can range from 0-100 percent.

The length of time from application to high tide (i.e. dry time), wind and weather conditions, application method, and timing of application in the plant's life cycle are all important factors. Efficacy can range from 0-100 percent.


Aquatic herbicide application. Aquatic herbicides have proven to be highly effective in eradicating populations of cordgrasses. Imazapyr and glyphosate are the only herbicides currently approved by the U.S. Environmental Protection Agency (USEPA) and the California Department of Pesticide Regulation (CDPR) for use in estuarine environments. While glyphosate has been available for estuarine vegetation management in California for some time, imazapyr was registered for estuarine use in the State of California on August 30, 2005. Both imazapyr and glyphosate herbicides are systemic broad-spectrum herbicides that are normally applied to and absorbed by foliage, and are circulated (translocated) throughout the plant and down into the belowground roots and rhizomes (a horizontal underground stem that sends out roots and shoots from buds). Because Spartina clones propagate rapidly via rhizomes, the translocation of the herbicide into the rhizomes and their ensuing cell death effectively prevents further spreading of the clone once the aboveground portion of the plant has died. Both herbicides block specific enzymes in the synthesis of certain amino acids in plants. The ensuing disruption of protein synthesis leads to interference in cell growth resulting in chlorosis and tissue necrosis of new leaves. The Control Program will use a number of herbicide delivery systems including backpack sprayer, conventional spray truck, amphibious tracked vehicle, hovercraft, shallow-bottom boat, airboat, and aerial application via helicopter where appropriate. Because the application of herbicide is highly effective with very low environmental impact compared to non-chemical control methods, it is the preferred control option on about 95% of the Spartina treatment sites. For a full description of the mode of action of these herbicides and an evaluation of their potential toxicity, please refer to the Programmatic Environmental Impact Report (PEIR) for the Control Program (, and the Addendum of May 2005 ( which includes an environmental assessment by Leson & Associates (2005) specifically on the use of imazapyr to control Spartina in the San Francisco Estuary.

Imazapyr: Low Impact Tool for Invasive Spartina Control in the San Francisco Estuary
(Invasive Spartina Project Fact Sheet Series, Aug. 2006)
This brochure provides a broad overview.
(PDF, 683 KB)  

Hand-pulling and manual excavation. Manual removal methods are the simplest technology for removal of cordgrass. Manual removal includes pulling cordgrass plants out of marsh sediments or using hand-tools such as spades, mattocks, or similar tools to cut away as much cordgrass as possible within reach. Manual removal methods are effective primarily at removing aboveground plant parts, but are less effective at removing belowground rhizomes that rapidly regenerate shoots. Unless digging removes the entire marsh soil profile containing viable rhizomes and buds, its effect is equivalent to pruning, since roots left in contact with moist soil often retain viability and regenerate in place, or disperse to establish new populations. The vigor with which remaining rhizomes resprout and regrow is often proportional with the severity of the disturbance. Frequent re-digging and maintenance is needed to exhaust rhizome reserves of energy and nutrition, and the population of buds capable of resprouting.

Manual removal is most effective on isolated seedlings, or very young discrete clones (asexually reproduced colonies of cordgrass) or clumps. Manual excavation in tidal marshes is extremely labor-intensive. Most cordgrass colonies occur in soft mud in which footing needed for digging is impossible or hazardous, even for workers on platforms, mats, or utilizing snowshoe-like boots adapted for walking on mudflats. Because digging and excavation are not practical on larger areas and can cause relatively greater damage to the sensitive marsh environment as compared to aquatic herbicide, these techniques are the preferred control option on only about 4% of the Spartina treatment sites.

Mechanical excavation and dredging. Mechanical removal in marshes uses equipment specially designed for working in semi-terrestrial, semi-aquatic wetland environments, such as amphibious dredges fitted with excavators or clamshells, “cutterhead” dredges, or terrestrial excavators working from mat structures on the marsh surface. Some locations allow use of conventional shallow-draft, barge-mounted dredging equipment working within reach of the marsh from the margins of navigable channels, particularly at high tide. Where cordgrass colonies lie adjacent to levees or roadways, track -mounted excavators can work without entry into the aquatic or wetland environments. Mechanical excavation working to the full depth of the rhizome system (up to 1 foot) in tidal marshes has the potential to be significantly more effective than manual excavation.

Covering/blanketing. This method typically involves crushing the Spartina so that it is even with the substrate, covering the entire plant with opaque geotextile fabric, and firmly staking the cover completely around a patch of cordgrass. This excludes light essential to photosynthesis (transformation of solar energy to food energy), and “bakes” the covered grass in a tent of high temperature and humidity.

This technique can be used for small, discrete clones where the geotextile fabric can be fastened to the marsh surface securely with stakes for a sufficient period of time to kill the plants. High tides, high winds, and tide-transported debris common in tidal marshes often make this technique difficult or impossible. Care must be taken to cover beyond the edge of the clone to a distance sufficient to cover the expected vegetative expansion from the rhizomes for at least one growing season. If rhizomes spread beyond the reach of the blanketing cover, rhizome connections to exposed, healthy stems can translocate (pipe) foods to the stressed, starving connected portions of the clone under the fabric, and increase overall survival. Staking geotextile tents on soft mudflats is very difficult, and is not feasible in many situations.

Pruning, Mowing, burning, and flaming. Cordgrasses are well adapted to disturbances that “crop” or otherwise remove aboveground biomass. A single event that removes living or dead aboveground cordgrass biomass generally just stimulates cordgrass growth, and as soon as a cordgrass stand resprouts, it begins to “recharge” its roots and rhizomes with new food reserves. If vegetation is removed with frequency, roots and rhizomes are prevented from regenerating reserves of energy and nutrition and cordgrass begins to die back as its organs of regeneration and storage become exhausted. If the cordgrass is mown close to the mud surface, it also severs the connections that transport oxygen from the leaves to roots growing in extremely anoxic (oxygen-deprived) waterlogged sediment, an additional source of stress on the plant that may eventually lead to mortality.

Repeated close mowing may be used to increase physiological stress to a point that cordgrass cannot regenerate, but this method is only feasible to use on small discrete stands of Spartina. The use of mowing (or burning) for cordgrass eradication in open mudflats and marshes would require very frequent treatment of all aboveground growth until the cordgrass rhizome/root systems become exhausted. For robust stands of Atlantic smooth cordgrass hybrids, this may require weekly treatment for more than one growing season. Generally, this is not feasible on a large scale in these environments with very soft, unconsolidated sediments or complex channel networks that must be crossed to reach the plants. In these cases, repeated entry to the marsh can have a very damaging effect on native salt marsh vegetation, and would not be possible during the endangered California clapper rail breeding season (Feb. 1 to Aug. 31), as access to occupied sites is forbidden during this time.

Mown vegetation without viable seeds or propagules may be left in place or removed from the site. Vegetation containing viable seeds or propagules would require removal from the treatment site and disposal in a suitable area not conducive to cordgrass growth.

Controlled burning may be used in some situations to remove vegetation prior to other treatments, or to prevent pollen and seed dispersal in founder colonies invading new sites. Burning would be used only in suitable locations, and only during periods of low-wind conditions (especially early morning), when fire hazards in succulent vegetation of tidal pickleweed marshes would be manageable. Ignition, however, may be difficult in vigorous cordgrass stands on mudflats.

Burning may prove very useful prior to herbicide treatment to clear dense areas of standing dead cordgrass that remains from the previous year’s treatment. This standing “necromass” can be so dense in previously treated monocultures as to impede the herbicide’s contact with the seedlings and other new cordgrass growth on the site. Burning this dry dead plant matter could open up the area and allow the subsequent treatment to achieve more complete coverage, producing more consistent results.

Selective pruning (partial mowing with “weed-whackers” or flaming with hand torches) may be used to remove flowerheads and seedheads of discrete colonies to prevent flow of pollen from contaminating seed production of native cordgrass, and to prevent seed production within founding colonies. However, pruning would have little or no effect on the clone’s growth rate or overall health and must be followed up with other methods to control spread.

An additional technique that may be utilized is “chemical mowing”, or the use of low concentration herbicide applications applied aerially that simply stop seed production and slow vegetative expansion, but are not actually strong enough to kill the plants. Normally we would want to maximize our efficiency and eliminate as much Spartina as possible in a given treatment. However, some sites contain high densities of California clapper rail and little other vegetation than non-native cordgrass. In these cases, it may be advantageous to preserve the aboveground biomass as cover for the rail, while limiting the spread by disrupting seed production. This method would assist the cordgrass eradication efforts of adjacent landowners by ensuring that their lands were not re-infested from seed or vegetative propagules. These would be temporary measures as part of a phased treatment approach on selected sites, which would eventually be followed up with eradication methods.  

The methods discussed above have been selected from a larger set of potential control methods based on efficacy, damage to the marsh habitat, water quality impacts, cost, risk to human health and safety, and feasibility. Several other methods including flooding/draining, burning, crushing and mechanical smothering, and mechanical ripping/ flailing/maceration were evaluated in the ISP’s Programmatic EIS/R but are not currently included in the ISP Control Program.

Program Approach Implementation Strategy


Preserving Native Wetlands


Home About Contact