Main page Foliage Sporocarps (flowers) Rhizoids (roots) Control
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 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.
- Topdressing fertilizers is the number one way to INCREASE liverwort
growth and accelerate its spread through your container yard. By
incorporating fertilizers (into your media), you remove most of the nutrients
from the container surface (though not all nutrients) and thus make it more
difficult for liverworts to grow. Dibbling fertilizers will further
reduce liverwort populations. Dibbling involves placing the entire
amount of fertilizer for each container beneath the rootball of the liner
while potting up. Many fertilizer manufacturers recommend against
this practice due to concerns over liability. Some crops are sensitive
to dibbling fertilizers because of high salt levels being so close to the
plant's rootball. However, in our research, and the work of many
other scientists, indicates that many species of plants grow well when
fertilizers are dibbled. In fact, dibbling fertilizers generally results
in superior plants compared to incorporating fertilizers, and similar sized
plants compared to topdressing. Many nurseries use this method routinely.
Before dibbling fertilizers with your plants, conduct small trials
to see if it works with your cropping system. Also, only use products
that are rated to deliver nutrients for 8 to 9 months or longer. Controlled
release fertilizers that release their nutrients in 3 to 4 months are more
likely to injure your crops when dibbling. And it is generally better
to dibble fertilizers in the spring, and not in late fall (due to potential
build-up of salts during extremely cold conditions of winter).
- Consider ways to modify your irrigation practices to limit overwatering.
Many growers overwater their container crops. Water is abundant,
and generally overwatering will not injure crops (except in some cases
where overwatering causes root disease). So it is 'safer' for growers
to overwater rather than risk under-watering. However, liverworts (and
pearlwort) thrive in wet conditions, and any practice that limits the amount
of water will decrease liverwort vigor.
- Changing your media to a mix that has better drainage will also
reduce liverwort vigor. Coarse media that drains well, especially near
the surface, is ideal. Coarse bark, pumice, perlite, and vermiculite
would work well to increase drainage. Peatmoss, choir, compost, sawdust,
and fine bark will increase a media's water holding capacity and thus increase
liverwort vigor. For optimum liverwort control and optimum crop growth,
try to develop a mix that is coarse enough so that it dries on the surface
rapidly, but fine enough to retain and provide adequate water to crop roots
below the surface of the container.
- Another way to decrease liverwort vigor is to increase air flow
throughout your crop (and thus decrease humidity near the container surface).
Can you lift the sidewalls of your hoophouse, or raise the sidewalls
of your Cravo? Can you arrange your plants with wider spacing or in
straighter rows to increase air circulation between plants and around the
container surface? Anything that increases airflow and decreases humidity
should help reduce liverwort vigor.
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:
- My experience is that Roundup provides poor liverwort control (which
of course can only be used on nursery floors, and not in containers).
- Acetic acid (5%) provided excellent liverwort control, and can
be used as long as you use products
containing vinegar that are legally labeled for weed control..
- In general, products used for postemergence liverwort control will
work better if sprayed before sporocarp
formation (personal communication with Sven).
preemergence herbicide trial for liverwort control
2003 postemergence herbicide trials for liverwort control
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