The control of Alternanthera philoxeroides with herbicides: a review
Alternanthera philoxeroides (Amaranthaceae, EPPO List of IAP) is so far only recorded in France and Italy in the EPPO region. It is invasive in other parts of the world, such as Australia, China, India, New Zealand, USA and the control of A. philoxeroides is generally considered to be difficult.
A. philoxeroides is more vigorous in aquatic habitats, but it also occurs in terrestrial habitats including pastures, urban areas and arable crops. As a consequence, other than threatening native plant communities by forming dense stands, A. philoxeroides also competes with pasture species, and crops such as rice for which yield losses of up to 45% have been reported.
This plant requires a warm growing season but can tolerate a wide range of climatic conditions, including winter frosts, which will kill exposed material. Although it is able to flower, seeds are not reported in its introduced range and the plant reproduces solely by clonal growth. Fragments of the plant are spread naturally by water.
The plant exhibits a phenotypic plasticity with its different growth forms occurring in aquatic and terrestrial environments, which is an important adaptative strategy to allow the plant to establish in a wide range of habitats. Differences in morphology may affect herbicide control efficacy. In addition, a number of other factors are considered to play a role in the tolerance of A. philoxeroides to herbicides, such as:
- Poor translocation out of leaves;
- Poor translocation to roots resulting in sub-lethal tissue concentrations;
- Exudation of glyphosate (and possibly other herbicides) by underground tissues;
- Poor translocation to quiescent buds;
- Auto-abscission or breakage of nodal tissue with high herbicide concentrations.
Evidence suggests that soil-applied herbicides provide better control than foliar-applied herbicides, this may be because the issue of poor translocation is circumvented.
The plant can be controlled effectively with glyphosate, although the management of subsequent fragments may be necessary. Substantial biomass reductions are achieved when multiple applications of herbicide are made per year. For example in Australia, the best control of A. philoxeroides has been obtained with imazapyr and metsulfuron-methyl, although satisfactory results have also been reported with glyphosate and triclopyr TEA.
Dugdale TM ; Champion PD (2012) Control of alligator weed with herbicides: a review. Plant Protection Quarterly 27(2), 70-82.