Based on the techniques that are currently being utilised by industry to manage sagittaria in Australia. The
options that are proven to be effective include:
Applying the herbicide glyphosate in all situations at high rate (3 to 10 times label rate, permit
required), up to three times per year. There is some evidence that a single application per year in
autumn will prevent further spread, but strong evidence that three applications per year (Nov, Feb
and Apr) will prevent seed production and reduce sagittaria abundance substantially. Reportedly,
efficacy is greater when water levels are low. There are however resistance issues due to over use of as single chemistry.
Physical removal techniques to mechanically or manually remove infestations are widely used in
sagittaria management. These techniques are used to restore irrigation channel function and prevent
further spread and establishment. Mechanical excavation has been utilised to eradicate outlier
infestations. These methods are cost prohibitive at a large scale and difficult to implement effectively when infestations have increased to cover large areas. At a site scale, manual removal has also been utilised but this method is very labour intensive, requiring great effort to produce effective results, the technique is generally utilised against low density populations and new outbreaks, with the aim of achieving site eradication.
The herbicides imazapyr and dichlobenil can be utilised effectively. However, only in specific situations where permits and label restrictions can be complied with, which effectively restricts their use to irrigation channels under certain conditions and on‐farm irrigation systems, respectively. Therefore, where small infestations are present and access allows, infestations should be removed via mechanical excavation.
Although this is expensive, control is effective where all material can be removed, including seeds and tubers in the sediment. To achieve this, at least the top 30 cm of sediment should be removed. It is critical to ensure machinery is clean when it leaves infested sites and that any sediment and plant material is disposed of where it cannot re‐infest waterbodies.
Where infestations are larger and targeting eradication is not feasible, the herbicide glyphosate is the most useful option, provided glyphosate is applied at high rate and three times per year (permits required). Specific
detail to improve the effectiveness of regimes using glyphosate are not available (e.g. timing, water level, which proprietary formulation, etc.). Likewise, further information to refine glyphosate regimes for eradication versus containment is not available.
Consideration can be given to the herbicides dichlobenil and imazapyr, which will both give more effective control, but only under minor use permits or within the label restrictions. TThe option of using either of these herbicides, or others listed in Section 3.4, provide the most likely alternatives to advance sagittaria management in the long term.