The experimental researches and practices on control and management of S. alterniflora are carrying through, although the functional evaluation of the invasion of the species could come to an agreement (Grevstad et al., 2003; Hedge et al., 2003; Major et al., 2003). The main eradiation or control methods include mechanical method, chemical method, biocontrol method and comprehensive eco-control method.
The mechanical methods is comprised of hand-pulling or manual excavation, covering with special cloth, creating dike to flooding or draining, continuing mowing, flaming, etc.. The effect of hand-pulling is significant for seedling of S. alterniflora. While, for clones or swards of S. alterniflora, it is difficut to pull or excavate by hands. Furthermore, the clones distribute on mudflats and the substrate is soft. Thus, the feasibility of hand-pulling or manual excavation is very small. Experimental results indicated that covering with special cloth for succession two growing season could effectively control small patch of S. alterniflora (Spartina Task Force, 1994). Continuing mowing could restrain the growth. However, it is necessary to mow nine to ten times from spring to autumn, and it must be three to four years for fully eradication of S. alterniflora, and the strategies directly influence the control effects (Taylor C. M. & Hastings, 2004).
The chemically methods is using herbicide to control S. alterniflora. In the chemical control practice in an estuary in the USA, N-(phosphonomethyl) glycene (glyphosate) was the most herbicide registered for aquatic use. The second was the solution of Arsenal (±-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5 -oxo-1H- imidazol-2-yl] -3 -pyridinecarboxylic acid) (Patten, 2002, 2003). The effects of herbicides varied with time and place when or where herbicides were used. Moreover, the effectiveness of herbicides on Spartina infestations appears to be highly variable with considerable variation between application methods. Low volume aerial application at permitted concentrations, although relatively inexpensive at approximately $420 per ha, has been far from impressive with combined mean efficacies of approximately 30% (Major et al.,2003). Wicking and wiping methods have also produced variable results. These methods are not cost effective and only suitable for small infestations. High volume hand held spray applications have been the preferred Rodeo application methods for Spartina control in Washington. Some trials report that Rodeo produces efficacies from zero to 50% (Patten 2000). However, others (Crockett 1997) report efficacies ranging from 85 to 97% control with 1 to 5% solutions of Rodeo sprayed to wet. The major parameters influencing efficacy appear to be the interaction of tidal elevation and period of time from post-spraying to tidal inundation and leaf cleanliness (Crockett, 1997; Patten, 2003).
Herbicides are noxious, and they maybe directly or indirectly impact to the health of human being, fauna and flora (Chen et al., 2004). Thus, the further studies are recommended for herbicide application for S. alterniflora controls.
The looking for and releasing natural enemy become one of the hotspots about biological invasion due to the advantages of biological control, such as durative efficacity, inexpensive cost, and ecological safety. The most promising biocontrol agent appears to be a Homopteran plant hopper (Prokelesia marginata) that feeds on the vascular fluids of Spartina species by piercing the leaf with its stylet (Daehler & Strong, 1995). The other animals in biocontrol practice are P. dolus, Delphacodes penedetecta (Hemiptera: Delphacidae) (Huberty & Denno2001; Ferrenberg & Denno, 2003). The ergot fungus, Claviceps purpurea, also has potential as a biocontrol agent. Littoraria irrorata, Melampus bidentatus, Geukensia demissa, Orchelimum fidicinum, Conocephalus spartinae (Silliman & Zieman, 2001; Grevstad et al., 2003; Pennings & Silliman, 2005). However, some questions are uncertain for the anfractuous interactions between / among biology, such as whether natural enemy will impact to other biology besides Spartina, and introducing natural enemy probably results to new biological invasion. There are arguments about natural enemy introduction, and the status of biocontrol for Spartina is experimental researches.
The principle of ecological control is that according the regular of community succession, using native species with economic or ecological value to replace invasive species through altering the habitat conditions. Bonilla-Warford & Zedler (2002) reported that invasive species Phalaris arundinacea had been replaced successfully by native species Spartina pectinata. The growth of Spartina had been restrained by transplanting Sonneratia apetala in Aoqidao of Zhuhai, Guangdong Province, China (Wang et al., 2003). There are some experimental practices to control S. alterniflora in the salt marsh of Jiangsu Province, China through constructing dike to restrain the dispersal of rhizome of S. alterniflora. At the same time, irrigation with fresh water reduces soil salinity and reconstructs the Phragmites australis wetlands.
The ecological and economic consequences of Spartina invasion varies with the local geographical characteristics and the process of oceanic dynamics. According the results of San Francisco Bay and Willapa Bay, it is very difficult to fully eradicate S. alternilora (Daehler & Strong; 1996). Thus, a more ecosystem-based approach to management, including control, needs to recognize the overall, long-term ecological role of S. alterniflora in the world (Hedge et al., 2003; Majoret al., 2003, 2004). The strategies include limiting the distribution of S. alterniflora through ecological engineering, and at the same time, exploring the economical value of the species. Total flavonoids and biologically mineral liquor could be distilled from the stems of S. alternilora (Qin & Chung, 1992), and the residue could be used as culture medium of mushroom. The strategies not only avoid pollutions but also increase the output of the ecosystem (An & Chung, 1991, 1992; Qin & An, 1998).
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