Mechanical and chemical control of smooth cordgrass in Willapa Bay, Washington

摘要

We evaluated four methods to control smooth cordgrass (Spartina alterniflora Loisel), hereafter spartina, in Willapa Bay, Washington: mowing, mowing plus herbicide combination, herbicide only for clones, and aerial application of herbicide for meadows. We used a single-hand application of Rodeo(R) formulated at 480 g L-1 acid equivalence (ae) of the isopropylamine salt of glyphosate (Monsanto Agricultural Co., St. Louis, MO; currently Dow AgroSciences, Indianapolis, IN) with the non-ionic surfactant LI 7000 (2.0% v/v) on clones, and a single aerial application with X-77 Spreader(R) (0.13% v/v) on large meadows. We compared efficacy using changes in stem density and stem height I yr post-treatment. Stem densities and heights within clones were reduced by all treatments. The mowing plus herbicide combination and single-hand spray were equally more efficacious than repeated mowing at two sites, whereas at a third site, the mowing plus herbicide combination was the most efficacious. Aerial application of the herbicide resulted in an average of 91% of intended deposition, but both treatment and control plots showed similar increases in stem density and decreases in stem height. A subsequent aerial application of glyphosate with the non-ionic surfactant, R-11(R) to the study area the following year resulted in no statistically significant change in stem density on our former treated plot, but stem height decreased. However, on our former control plot, stem density significantly decreased, whereas stem height increased. We conclude that the mowing plus herbicide combination consistently provided the best control of clones, but hand application of the herbicide was almost as efficacious. The aerial herbicide applications we monitored provided little or no control indicating the need to improve efficacy if aerial treatment is to be a viable control strategy.