at 92% of continuous swards, while lower doses (0.45 – 1.35 g/m 2 ) removed <40% (Zhao et al ., 2020).
Surfactants in herbicides: Surfactants are chemicals that allow herbicides to disperse more easily in water. Evidence suggests that glyphosate-based herbicides can be toxic to aquatic organisms, such as amphibians, water fleas and fish and this toxicity has been linked to the concentrations of surfactants in the herbicide (Pless, 2005; Mikó & Hettyey, 2023).
Case study: San Francisco Bay, USA
Spartina alterniflor a was introduced to San Francisco Bay in the 1970s. S. alterniflora crossed with the native species S. foliosa , producing some hybrids that grew vigorously. The Spartina hybrids outcompeted the natives and expanded their range due to their higher tolerance to inundation and salinity. The presence of the native S. foliosa , which is valuable in structuring the shoreline, makes controlling invasive S. alterniflora more difficult. The spread of S. alterniflora led to an estimated loss of 27 – 80% of the foraging area for birds. A federal state programme to eradicate Spartina was established in 2003 and herbicide application began in 2005. The herbicide used was imazapyr, which is one of only two herbicides permitted to be used in estuaries in California. Imazapyr was applied using helicopters, all-terrain vehicles, boats, and on the ground with backpack sprayers. In 2005, S. alterniflora and Spartina hybrids covered 327 ha of the Bay. By 2019 coverage was 11.4 ha. This equates to a reduction of 96%.
From 2000 – 2001 the total cost of the Invasive Spartina Project was 21 million US dollars.
Lessons learned:
● Between establishing the programme in 2000 and implementing the programme in 2005, S. alterniflora spread extensively. Therefore, delaying treatment made Spartina removal even more difficult. ● Mapping S. alterniflora occurrence before herbicide application would mean applicators do not have to decide where to spray, saving time. ● The herbicide requires six hours of drying time (depending on the weather conditions), therefore the timing of application is critical in terms of weather and tides. It should also be applied during the growing season before seed set.
Source: Strong & Ayres (2013, 2016)
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