Topramezone Herbicides were registered for aquatic use U.S. EPA in late 2013. It is currently sold under the trade name Oasis®. It is a systemic herbicide that is applied to the water column for submersed plant control, directly to foliage of floating and emergent vegetation, or dewatered sites. Topramezone is the first herbicide belonging to new chemical class called pyrazolones. In sensitive plant species, topramezone inhibits the enzyme 4-Hydroxy-Phenyl-Pyruvat-dioxygenase (4-HPPD) leading to a disruption of the synthesis and function of chloroplasts. Consequently, chlorophyll is destroyed by oxidation resulting in bleaching symptoms of the growing shoot tissue (white or pink coloration) and subsequent death of the above ground portion of the pant.
Topramezone is newly registered and is under evaluation to determine optimum exposure periods and concentrations for hydrilla control. Generally, topramezone is applied at 30-50 ppb and maintained at or near the initial concentration for a minimum of 60 days. Applications are made to actively growing plants early in the growing season before mature plants can build carbohydrate reserves, mat at the water surface, and slow growth and subsequent herbicide response. Topramezone is absorbed into the plant tissue and symptoms generally first appear in 7-10 days. Topramezone is under evaluation for foliar applications to control water hyacinth and water lettuce.