ARS | Publication request: Influence of application timing on the impact of glyphosate on giant reed (Arundo donax L.)

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 2011
Publication Date: January 27, 2012
Citation: Spencer, D.F., Ksander, G.G., Tan, W., Liow, P., Whitehand, L.C. 2012. Influence of application timing on the impact of glyphosate on giant reed (Arundo donax L.). Journal of Aquatic Plant Management. 49:106-110.

Interpretive Summary: Giant reed is an invasive plant of riparian habitats. There is little data on the efficacy of glyphosate treatments made at different times in giant reed’s life cycle that could be used to select an appropriate application regime. We conducted two experiments where 1.5% glyphosate had been applied to different life cycle stages. By one year after treatment all of the treated container-grown plants at Davis did not have any living stems regardless of the treatment month. For naturally grown giant reed near Fresno, plants treated in September had significantly lower leaf greenness than untreated plants while plants treated in the other months did not show detectable differences from each other or the untreated plants. Plants treated in September and October had the lowest proportion of living stems per square meter one year after treatment. The lowest number of new stems produced was observed for plants treated in September. These results indicate that September treatments with 1.5% glyphosate resulted in greater kill of giant reed than treatments applied in other months. Differences between the field and container-grown plants were likely due to smaller plants in the containers which may be less able to recover from damage due to the reduced rhizome mass. These results are important if the goal is to minimize the number of treatments, reduce labor costs, and minimize impacts on sensitive habitats by reducing the number of site visits and the amount of herbicide used.

Technical Abstract: Outdoor experiments were conducted at Davis, California and near Fresno, California. Plants received an application of 1.5% glyphosate solution in either September, 2006, October, 2006, November, 2006, April, 2007, June, 2007 or August, 2007. Leaf greenness, number of living and dead stems, and the number of newly emerging stems were measured monthly until September 2008. By one year post treatment all of the treated container-grown plants at Davis did not have any living stems regardless of the treatment month. For naturally grown giant reed near Fresno, plants treated in September had significantly lower leaf greenness values than untreated plants while plants treated in the other months did not show detectable differences from each other or the controls. Plants treated in September and October had the lowest proportion of living stems m-2 one year after treatment. The lowest number of new stems produced was observed for plants treated in September. These results indicate that September treatments with 1.5% glyphosate resulted in greater kill of giant reed than treatments applied in other months. Differences between the field and container-grown plants were likely due to smaller plants in the containers which may be less able to recover from damage due to the reduced rhizome mass.