The use of adjuvants in aquatic weed control: good idea or bad practice?

Presentation at South Carolina Aquatic Plant Management Society Annual Conference 2014. This talk presents data on the effects of glyphosate applications at full, half and quarter rate, in combination with the aquatic approved adjuvant TopFilm. The aim of the research was to determine if the proposed EQS for glyphosate, due for implementation in 2018, would affect the ability of aquatic wed managers in the UK and Europe to undertake effective aquatic weed control.. preliminary analysis of the data show that application of half rate glyphosate (2.5 litres per hectare of a 360 g/L formulation Roundup pro Bio) gave similar levels of control to the normal full rate application. Experiments were carried out in a 3 block split plot design with 6 treatments and once untreated control at each site. In one site the reeds were growing in a terrestrial environment out of the water but along a north facing bank, at another site the reeds were growing in shallow water at the toe of the bank and up the bank, and at the third site all the treated reed were growing in shallow water approximately 30 – 40 cm deep. Control appeared to be dose dependent at the two sites with some terrestrial influence, but complete control was achieved at all dose rates when reeds were growing in water. Measurements of regrowth were made in June and October one year after treatment. The June observations showed good control, even at the lower doses, but the October measurements showed regrowth in the plots treated with low dose rates. Most regrowth was from seedling recruitment as the plants observed had no flowers. Where flowers were present in the control plots, this indicated a lack of control of growth form an existing rhizome structure. The talk also addressed the apparent lack of regulation of adjuvants for aquatic weed control and offered a warning about timely defence of their use in protecting natural resources in the USA.