Endothall behavior in Myriophyllum spicatum and Hydrilla verticillata

Abstract

BACKGROUND: Endothall has been used to control submersed aquatic plants since 1960, providing broad-spectrum control of aquatic weeds. Although endothall is considered a contact herbicide, many field observations suggest that it might have systemic activity. The goals of this research were to determine endothall's (i) absorption characteristics, (ii) translocation from shoots to roots, and (iii) potential for desorption in Eurasian watermilfoil (EWM), monoecious and dioecious hydrilla. RESULTS: Endothall absorption was linear in dioecious hydrilla up to 192 HAT, while in EWM and monoecious hydrilla absorptiondata best fit an asymptotic rise function. Endothall absorption in EWM, monoecious and dioecious hydrilla was 3.3, 6.6, and 11.0 times the external herbicide concentration determined by the plant concentration factor. Translocation to EWM roots reached 7.9% of total absorbed radioactivity by 192 HAT, while translocation to monoecious and dioecious hydrilla roots reached 17.8% and 16.4% by 192 HAT, respectively. For all three species, no more than 30% of absorbed endothall moved from the plant to clean water 96 HAT. CONCLUSION: Endothall is a very water soluble compound and yet it accumulated in these three important aquatic weeds at concentrations significantly higher than the external herbicide concentration. These data provide evidence that endothall could have systemic activity in these aquatic species. Following 14 C-endothall applications, more 14 C translocated from shoots to roots compared to the translocation of 14 C for other systemic aquatic herbicides. The final confirmation of endothall's systemic behavior requires that the radioactivity found in the root system of these aquatic plants is 14 C endothall.

2,4‐D and 2,4‐D butoxyethyl ester behavior in Eurasian and hybrid watermilfoil (Myriophyllum spp.)

“…After only 1 h 2,4‐D BEE PCF was 16.78 ± 0.32, 30 times greater than 2,4‐D's PCF at the same time (0.53 ± 0.01). Even though 2,4‐D and 2,4‐D BEE bioaccumulation was greater in HWM than in EWM, increased herbicide accumulation does not necessarily equate to better control 25 and therefore, herbicide absorption does not contribute to 2,4‐D resistance in HWM. One possible explanation for greater herbicide accumulation in HWM could be due to its faster growth rate and lower herbicidal impacts on plant growth.…”

“…31 Another study looking at aquatic herbicide desorption demonstrated that although endothall's log K ow is −0.55, it binds irreversibly to several serine/threonine protein phosphatases; therefore, endothall's desorption in EWM by 96 HAT was only 28.92% ± 15.63% well below equilibrium with the water column. 25 Even though HWM desorption was slightly lower than EWM, 2,4-D and 2,4-D BEE desorption in both plant species is driven mainly by a concentration gradient, and the establishment of a dynamic equilibrium between the shoots and water column; therefore, herbicide desorption does not appear to play a role in 2,4-D resistance in HWM.…”

“…Tubes were filled with unwashed silica sand and a layer of low melting point eicosane wax (Eicosane 99%, Fisher Scientific, USA) was applied to the surface to isolate the root system from the water column. 24,25 Transplanted plants were kept in the laboratory for 2 days prior to treatment to acclimate. For desorption and metabolism experiments, non-rooted 10 cm apical shoots were collected from EWM and HWM stock populations.…”

“…Roots of selected plants were rinsed with tap water to remove any soil residue and transplanted into 15 mL plastic conical centrifuge test tubes (Thermo Fisher Scientific, USA). Tubes were filled with unwashed silica sand and a layer of low melting point eicosane wax (Eicosane 99%, Fisher Scientific, USA) was applied to the surface to isolate the root system from the water column 24,25 . Transplanted plants were kept in the laboratory for 2 days prior to treatment to acclimate.…”

Current Status and Future Prospects in Herbicide Discovery

“…Inhibitors, such as cantharidin and endothall, bind to a hydrophobic pocket of the PP active site. Endothall is a very effective herbicide to manage weeds in aquatic environments [34].…”