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Marchantia polymorpha may be the most troublesome weed problem in containers (in Oregon).

Before talking about how to kill liverworts, let's talk about conditions in which liverworts thrive.  Liverworts grow vigorously in conditions with high humidity, high nutrient levels (especially nitrogen and phosphorus), and high soil moisture.  In an environment that has any of these 3 conditions, it will be difficult to control liverworts (even when using herbicides).  In order to effectively control this weed, you must make growing conditions for the liverworts as difficult as possible.  To do this, you should attempt to create an environment where the ambient air is dry, the surface of the container is dry (as dry as possible), and nutrients are not available on the container surface.  

Preemergence Control

Preemergence is the best way to control liverwort, however, liverwort cannot be controlled with herbicides alone.  For effective control, you must use cultural practices that deprive liverworts of the moist, high fertility, and humid conditions it thrives in.  And for added control, a preemergence herbicide along with modification of your cultural practices will help considerably.  

Postemergence Control

There are no herbicides labeled for postemergence liverwort control in containers.  Sven Svenson did a great deal of work on postemergence control, however, the products he found to be successful were generally also phytotoxic to nursery crops as well, or not labeled for nursery crops (and thus not legal).  So, it does no good for me to list products that are illegal to use anyhow.  But here are a few points to consider:

2003 preemergence herbicide trial for liverwort control

2003 postemergence herbicide trials for liverwort control

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