Technical Report No. 8

EFFECTS OF APPLICATION OF GLYPHOSATE ON THE EELGRASSES ZOSTERA MARINA AND ZOSTERA JAPONICA IN PADILLA BAY, WASHINGTON

Douglas A. Bulthuis and Travis C. Shaw

December 1993

Bibliographic Citation
Bulthuis, Douglas A. and Travis C. Shaw. 1993. Effects of application of glyphosate on the eelgrasses Zostera marina and Zostera japonica in Padilla Bay, Washington. Washington State Department of Ecology, Padilla Bay National Estuarine Research Reserve Technical Report No. 8, Mount Vernon, Washington. 45pp.

Abstract
The herbicide, glyphosate (Rodeo® with X-7® spreader), was applied at five concentrations with a backpack sprayer to intertidal Zostera marina and Z. japonica and onto subtidal Z.marina whose leaves were floating on the water surface during low tide. Glyphosate was applied in July, 1992 during some of the lowest tides of the year to maximize the time of exposure before inundation of the eelgrasses by high tide. Glyphosate had no consistent effect on Z. marina nor Z. japonica in either microhabitat in the two months following application as measured by density of shoots, percent cover of live and dead leaves, above- and below-ground biomass or concentration of chlorophyll in the leaves. Nor was there any difference between treatment and control sites 12 months after application as measured by density and above ground biomass. It is suggested that the glyphosate did not have any measurable effect because of water retained on the leaf surface reducing absorption of the herbicide and because of the short time of exposure to the herbicide (three hours or less) before the flooding tide.