Use of herbicides to control alligatorweed and restore native plants in managed marshes

Published source details Allen S.L., Hepp G.R. & Miller J.H. (2007) Use of herbicides to control alligatorweed and restore native plants in managed marshes. Wetlands, 27, 739-748.
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This study is summarised as evidence for the following.

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	Use herbicide to control problematic plants: freshwater marshes Action Link

Use herbicide to control problematic plants: freshwater marshes

A replicated, randomized, paired, controlled, before-and-after study in 2004–2005 in two freshwater marshes invaded by alligatorweed Alternanthera philoxeroides in Alabama and Georgia, USA (Allen et al. 2007) found that spraying the vegetation with herbicide had no significant effect on native plant biomass after 1–2 growing seasons. Native plant biomass varied a lot depending on herbicide type, dose and application date, but was statistically similar in sprayed and unsprayed plots in 24 of 24 paired comparisons (sprayed: <1–210 g/0.25 m²; unsprayed: 76–129 g/0.25 m²). Alligatorweed biomass did not significantly differ between treatments in 14 of 24 comparisons (for which sprayed: 18–92 g/0.25 m²; unsprayed: 54–78 g/0.25 m²) but was lower in sprayed plots in the other 10 comparisons (for which sprayed: <1–22 g/0.25 m²; unsprayed: 54–78 g/0.25 m²). The study also provided short-term data on alligatorweed cover. This was depressed after 2–4 weeks for all herbicide types, doses and application dates (sprayed: 0–32%; unsprayed: 25–69%; before spraying: 17–62%). Methods: Sixty-four 5 x 5 m plots (in four sets of 16) were established across two alligatorweed-invaded freshwater marshes, managed for waterfowl. Herbicide was applied to 48 of the plots (12 random plots/set), in all possible combinations of herbicide type (triclopyr amine or imazapyr), dose (low, medium or high) and application date (April or July 2004). Alligatorweed cover was surveyed one week before spraying and for 12 weeks after. Vegetation was cut from plots, then dried and weighed, in October 2004 and 2005.

(Summarised by: Nigel Taylor)