Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2014
Publication Date: 7/22/2014
Publication URL: http://1080/03601234.2014.922397
Citation: Spencer, D.F. 2014. Evaluation of stem injection for managing giant reed (Arundo donax). Journal of Environmental Science and Health, Part B:Pesticides, Food Contaminants, and Agricultural Wastes. 49:(9) 633-638. DOI:10.1080/03601234.2014.922397
Interpretive Summary: Giant reed is an invasive plant of riparian habitats. One management approach is to treat plants with foliar sprays of herbicides. In some habitats where 1) threatened or endangered species live, 2) organic crops are grown nearby, or plants are growing in residential areas, foliar spray of herbicides may be restricted. An alternative treatment method is to inject herbicides directly into the hollow giant reed stems. However, there is little data on the efficacy of this approach with three commonly used aquatic herbicides. We conducted two field experiments to evaluate this approach. In the first experiment 5 ml per stem of concentrated glyphosate, imazapyr, or triclopyr were injected directly into the stem. Both glyphosate and imazapyr significantly reduced leaf chlorophyll level, the number of living stems in a clump, and the number of new stems produced during the year following treatment. In a second experiment the proportion of stems present in a clump that needed to be treated (0, 10%, 25%, or 100%) was evaluated. Based on the same growth responses as above all of the stems needed to be treated for maximum effect. These results imply that giant reed may be successfully treated by injecting full strength glyphosate (5 mL stem-1) into all of the stems within a clump. While labor intensive this method, offers a new method for managing giant reed in sensitive sites where foliar spray applications may be restricted.
Technical Abstract: Giant reed is an emergent aquatic plant that may be weedy throughout California and the United States. Two herbicides approved for controlling giant reed in California are glyphosate and imazapyr. Foliar applications of these herbicides may be restricted in sensitive areas, such as those which are within the range of threatened or endangered species. We conducted two field experiments at sites in northern and central California. The first experiment evaluated the effects of three aquatic herbicides (glyphosate, imazapyr, and triclopyr) injected into all of the stems within a giant reed clump (5 mL stem-1). In this experiment, leaf chlorophyll content, the proportion of living stems, and the number of new stems produced during the year after treatment declined significantly (> 80%) following injection of either full strength glyphosate or imazapyr. The effects of injecting full strength triclopyr were considerably less. In a second experiment, different proportions (0, 10%, 25%, or 100%) of the stems within a clump were injected with full strength glyphosate. Results indicated that it was necessary to inject all of the stems within a clump to achieve the greatest reduction in the plant growth characteristics measured. These results imply that giant reed may be successfully treated by injecting full strength glyphosate (5 mL stem-1) into all of the stems within a clump. While labor intensive this method, offers a new method for managing giant reed in sensitive sites where foliar spray applications may be restricted.