plants by hand. However, this is a slow process and would therefore be impractical at a larger scale (Hedge et al. , 2003).
Time of treatment: The time of the year the control measure is taken can influence its effectiveness. Evidence from China suggests that the optimal time for mowing is early June to early July, i.e. from the end of the vegetative growth period to the flowering stage (Xie et al. , 2019). Use of heavy machinery: It can be challenging to use heavy machinery in wet, soft, intertidal sediments. Furthermore, vehicles can displace or compress any vegetation present and could have potential adverse impacts on benthic invertebrates in the sediment (Evans et al. , 1999; David Melville, pers. obs.).
4. Implementation
Cutting or mowing: Cutting/mowing creates open areas more quickly than herbicides (David Melville, pers. obs.). Cutting and mowing can be done with hand-held equipment or with mowing machines (boats) capable of accessing both land and water. However, Hedge et al. (2003) reported that mowing machines were too fragile to use in estuarine environments. The timing of mowing needs to be considered. Sheng et al. (2014) found that this mowing reduced Spartina stem height but did not eradicate it. Herbicide: Current global practice suggests that the two most effective herbicides are haloxyfop and imazapyr, with high kill rates shown in New Zealand, USA and China (Brown & Raal, 2013; Strong & Ayres, 2016; Patten et al. , 2017; David Melville, pers. obs.). Other herbicides shown to negatively affect Spartina abundance include: imazameth, glyphosate, 2,2-dichloropropionic acid (commercially Dalapon) and cyhalofop butyl (Reynolds et al. , 2023). Given the small number of studies which have investigated the effectiveness of some individual herbicides, it is important to use caution when drawing conclusions about their ability to control Spartina at scale. Flooding: Flooding areas where Spartina grow can kill the roots by decreasing the oxygen availability. A study in China found waterlogging at depths of at least 30 – 40 cm is the most effective at reducing Spartina (Xie et al. , 2019). This was effective when combined with mowing in either June or August. This can only be done in areas where the water levels can be controlled over a longer time, so not on open tidal flats. Sheng et al. (2014) found that waterlogging and mowing together were the most effective at reducing Spartina. Covering: Spartina can be covered over temporarily with fabric to prevent photosynthesis and inhibit plant growth. Alternatively, Spartina can be covered with inter- or sub-tidal soils, but this can increase the height of the treated areas. Where this is carried out in the upper intertidal areas, it risks reducing the width of open tidal flat areas that are extremely important for feeding of migratory shorebirds (Mu & Wilcove, 2020). At a site in Xiaoyangkou, Jiangsu, China, placed sediment in fact provided roosting habitat for shorebirds. However, this was subsequently lost as Spartina grew up through dumped sediment (David Melville, pers. obs.).
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