Weed control is an important management area in containerized production of nurseries and greenhouses because the market value of ornamentals is determined primarily by their quality, appearance, and aesthetics. Liverwort (Marchantia polymorpha) is a notable problematic weed that exists in nursery and greenhouse conditions. It has a flattened thalloid body that forms a mat-like structure on the top of container media. It thrives well in propagation and container production environments with low ultraviolet radiation, high humidity and/or soil moisture, and high fertility. Hand removal of liverwort is a laborious, time-consuming, and costly operation. Not many herbicides are labeled for liverwort control inside greenhouses as most of them can cause severe phytotoxic damage to sensitive ornamentals. Hence, the goal of this research was to develop an integrated management approach for liverwort infestations in nurseries and greenhouses. Various non-chemical methods including organic mulching, strategic fertilizer placements and allelopathic properties of organic mulches; and chemical methods including pre- and post-emergence application of synthetic and organic herbicides were studied for their effects on liverwort control. Absorption and translocation of 14C labeled radioactive 2,4-D and indaziflam in liverwort thallus were assessed by liquid scintillation spectrometry and phosphor imaging. Results indicate that mulching with rice hull and pine bark provided an excellent liverwort control and no phytotoxicity to Hosta spp. varieties ‘Curly Fries’ and ‘Pandora Box’. Thicker layers of mulching with cocoa hull and hardwood mulches caused phytotoxicity to ‘Curly Fries’ and ‘Pandora Box’, respectively. The sub-dressing and dibble placements of controlled-release fertilizers improved growth of dicot Begonia and monocot Dracaena while minimizing the fresh biomass of liverwort in containerized production. Agar impregnated with maple leaf and shredded cypress mulch based allelopathic extracts showed maximum suppression of liverwort gemmae germination in growth chamber studies. Whereas allelopathic extracts from pine bark and hardwood mulches were most effective for liverwort control under greenhouse conditions. The post-emergence application of glyphosate and 2,4-D at 1X rate and indaziflam at 2X and 3X rates were effective in controlling liverwort. Also, pre-emergence application of indaziflam provided complete inhibition of liverwort gemmae germination and establishment. In the 14C absorption and translocation studies, the total recovery of 14C radiolabeled 2,4-D ranged from 63-80% while it ranged from 49-80% for 14C radiolabeled indaziflam. Phosphor imaging of the translocation samples of liverwort thallus displayed higher movement of 2,4-D as compared to indaziflam in liverwort thallus. The organic herbicide treatments of WeedPharm and Scythe at 2X rate and Avenger at 1X rate provided season-long liverwort control. Overall, a proper utilization of multiple tactics including cultural methods (mulching and strategic fertilizer placement), allelopathy, and chemical methods (pre- and postemergence herbicides) can lead a way to develop an effective integrated control program for liverwort in nurseries and greenhouses.
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