Impact of herbicide retention time on the efficacy of foliar treatments for control ofcrested floating heart

摘要

Crested floating heart [Nymphoides cristata (Roxb.) Kunt-zel], hereafter referred to as CFH, is a floating leaf plant native to Southeast Asia where it is considered a common weed in rice fields (Burks 2002). In the United States, CFH is found throughout Florida and has recently spread to Louisiana, North Carolina, South Carolina, and Texas (Willey 2012). Currently, there are no host-specific insect herbivores that feed on CFH, and grass carp are ineffective as a control agent (Singh et al. 1966, Willey and Langeland 2011). Mechanical harvesting and winter drawdowns have also proven ineffective at controlling CFH (Middleton 1990, Willey and Langeland 2011). Initial herbicide screening conducted by Willey et al. (2014) found that a subsurface application of endothall or diquat or a foliar application of imazamox or imazapyr are the most effective means to control CFH. Foliar applications of flumioxazin alone and in combination with glyphosate as well as foliar applications of carfentrazone-ethyl plus glyphosate were also effective at reducing CFH biomass in small-scale trials (Glomski et al. 2014). Although several herbicides have been identified as having activity against CFH in small-scale trials, ongoing management efforts in the field have beeninconsistent. Some resource managers have suggested that for foliar-applied treatments, rapid loss of herbicide from the surface of the CFH leaf may be attributed to disturbances from boat wakes or wave action. In comparison with native floating-leaf plants such as nuphar (Nuphar advena), water lily (Nymphaea odorata), and American lotus (Nelumbo luted), CFH has a much smaller leaf and grows from individual root crowns versus formation of extensive underground rhizomes. Although the native "lilies" can require management in some situations, they are typically considered valuable habitat and there is limited published work focusing on control of these plants.