Technical Report No. 9

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

Douglas A. Bulthuis and Mary Jo Hartman

October 1994

Bibliographic Citation
Bulthuis. Douglas A. and Mary Jo Hartman. 1994. Effects of application of glyphosate during summer on epiphytes of 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. 9, Mount Vernon, Washington. 40 pp.

Abstract
The herbicide glyphosate (Rodeo® with X-77® spreader) was applied at five concentrations with a backpack sprayer onto experimental plots at three sites: an intertidal Zostera marina site, an intertidal Z. japonica site and a subtidal Z. marina site at which the leaves were floating on the water surface at the time of application of glyphosate. 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 and epiphytes by the flooding tide. Application of glyphosate had no effect on biomass of epiphytes as measured by total chlorophyll content of the epiphyte community and total dry weight of epiphytes in the eight weeks following application at the Z. japonica site and at the subtidal Z. marina site. At the intertidal Z. marina site, total chlorophyll and chlorophyll c of epiphytes in the highest treatment plots was about one-half the biomass in the control plots after two weeks, but the glyphosate treatment had no effect on total biomass of epiphytes during the rest of the eight week study period. There was not any increase in the chlorophyll breakdown product, phaeo-pigment at any of the sites. It is suggested that the glyphosate had little measurable effect because water retained on the leaf surface reduced absorption of the herbicide and because of the short time of exposure to the herbicide (three hours or less) before flooding tide. The natural epiphyte community on Zostera marina fluctuated widely; total chlorophyll decreased by 1/4 during the eight week study period. The biomass of the natural epiphyte community on Zostera japonica was much lower than the community on Z. marina throughout the eight week study period.