Quinoclamine is an herbicide under development for control of liverwort, a weed common in nursery crops. With respect to liverwort control, quinoclamine has been considered to primarily have POST activity. However, some PRE activity has been reported. Growth media sorption studies with 14C-quinoclamine indicate that only 0.64% of the quinoclamine amount that enters the media remains unadsorbed and thus available to be taken up by established plants or propagules. Computer modeling revealed that a large portion of the surface of the quinoclamine molecule is positively charged, which likely is the reason for its high adsorptivity. In a simulation of PRE activity, hydroponically grown liverwort and germinating gemmae were exposed to increasing quinoclamine concentrations. Phytotoxicity to both plants and gemmae was obtained with a minimal concentration of 4 to 6 mg L−1. Based upon the projected use rate, and assuming minimal vertical infiltration depth, the theoretical concentration of quinoclamine within the aqueous phase of a pine bark substrate would be approximately 8 mg L−1. In toto, results indicate that the projected use rate will result in sufficient quinoclamine in the aqueous phase of a pine bark substrate to provide PRE control of gemmae propagules as well as to contribute to the efficacy of POST applications to established liverwort.
Nomenclature: Quinoclamine; liverwort, Marchantia polymorpha L.