Evaluating the efficacy of aquatic herbicides on emergent rotala (Rotala rotundifolia)

Carl J. Della Torre III, Lyn A. Gettys, Samantha N. Sardes


Rotala (Rotala rotundifolia) is a relatively new invader of flood control canals in south Florida. Rotala is well-controlled by 2,4-D and triclopyr, but irrigation restrictions associated with some auxin-based herbicides can limit their use because many homeowners, growers and other stakeholders draw irrigation water from flood control canals. In this project we examined the effects of most products labeled for aquatic use on the emergent growth form of rotala. Modes of action included three auxins, seven enzyme inhibitors (two PPO, three ALS, one EPSPS and one HPPD) and one unclassified product. Herbicides were tested at maximum and half-maximum label rates; a silicone surfactant was included in all mixes. The auxins performed as expected and the EPSPS inhibitor glyphosate had little effect on rotala. The PPO inhibitor flumioxazin was more efficacious than the PPO inhibitor carfentrazone but provided only short-term control. The most effective ALS inhibitor was imazamox, which resulted in better control than penoxsulam and bispyribac-sodium. Plants exposed to fluridone (PDS) and topramezone (HPPD) showed early characteristic bleaching; some regrowth occurred but regrowth was lower in plants treated with 16 oz/acre of topramezone than with 7.7 oz/acre of fluridone. Further testing is planned to evaluate combinations and a wider range of rates in non-auxin products that performed well in these experiments.

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283