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Herbicides form a chemical barrier over the
container media. Though each herbicide controls weeds differently,
they all provide control at the point which germinating seed emerge through
the chemical barrier. If the chemical barrier is disrupted, it will
create a gap where weed seed can successfully germinate and grow.
There are several common practices that disrupt the chemical barrier, these
include but are not limited to: poking holes in the barrier with your fingers
or hands while moving containers around, dropping containers, and containers
blowing over. All these activities should be minimized to prevent
disruption of the chemical barrier. Instruction and explanation of
this concept to the work crew is necessary, as they are typically the ones
responsible for moving and working around the containers. |
| Containers should be placed over some sort
of groundcover, usually stone or weed-fabric. While this method
is effective in suppressing weeds under the covered area, debris from
plants and spilled bark will create an environment where weeds can establish.
Weeds between containers are a source of weed seed (bittercress
and oxalis
can project seed several feet). Other weeds like eclipta
can become established in the drainage holes and out-compete the plant
for water and nutrients. So even the area under containers must be
maintained weed free. |
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Eliminating weeds in non-production areas
such as roadways, drainage ditches, between hoop houses, etc., will drastically
reduce weed seed number and improve weed control. This can be accomplished
with regular mowing of turf areas as long as it’s done often enough to
prevent turf weeds from setting seed. Mechanical removal such
as disking or plowing can be used, though this makes the area more susceptible
to erosion and washouts. Control with herbicides provides effective control. Postemergence herbicides can be used to eliminate existing weeds, and preemergence herbicides used to prevent re-growth. Maintaining weed-free non-cropland areas is probably the easiest and the most effective sanitary practice for reducing weed seed numbers in your containers. |
| Bark piles should be kept weed free.
Not only will these weeds generate seed that can be blown into containers,
but they can also deposit seed and/or vegetative propagules (tubers from
nutsedge, rhizomes from oxalis, etc.) directly
into the media that will eventually be used for potting. When bark
piles are kept weed-free, they do not contribute as a source of weeds (Cross
and Skroch, 1992). Steam pasteurization, solarization, composting,
and fumigation are some treatments that will kill seed and other propagules
in bark piles. These treatments are not likely cost effective for
most nursery operations, and simple sanitation will avoid the need for these
treatments. |
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Use of clean or new pots for propagation
and/or canning will also reduce the number of weeds in your nursery.
A study at Clemson University (Bachman and Whitwell, 1995) demonstrated
that by simply washing propagation pots with pressurized water, the number
of germinated weeds was reduced six-fold. Their study showed that
when dirty pots with debris around the edges were used, weeds (bittercress)
germinated around the edges of the pots, compared to few weeds when new
or cleaned pots were used. |
Use of weed free liners is critical, especially when dealing with
weeds that have extensive root systems such as oxalis, liverworts (rhizoids
instead of roots), and pearlwort. Because roots from these plants
can generate new plants, thorough hand-weeding to remove shoots and roots
is necessary. A single escape weed can generate new plantlets at
an alarming rate. One bittercress plant
can produce up to 5000 seed in just 5 weeks (Bachman and Whitwell, 1995).