January 2021 - 30

RESEARCH
CONTROLLING
WEEDS
in Container
Production
Can growers control weed growth in container production using strategic fertilizer placements?
BY DEBALINA SAHA
W
eeds can reduce the overall quality and market value of the
ornamental plants, as they compete for water, nutrients, space,
light and oxygen and can even harbor pests and pathogens. In
container production, weeds can reduce the growth of ornamental plants
by more than 50%, as they are more competitive with ornamentals in
restrictive growth environments.
In greenhouses and other enclosed structures, the main limitation for
weed control is the lack of herbicide options and their restrictions to be
used inside greenhouses. In addition, there are several ornamental species
that are sensitive to herbicides. Strategic placement of controlled release
fertilizers (CRFs) within the container can be used as an alternative method
to control weeds. CRFs can be placed within a container by four different
methods (Figure 1): top dressing, the container is filled with standard
substrate and then CRF is applied on the top of surface layer; subdressing,
the CRF is added in form of a layer at a depth of 2 inches from the top;
incorporation of CRFs is mixing of the fertilizer with the substrate and then
filling up the containers; for dibble, the CRF is placed in a small pocket at a
depth of 2 inches from the top.
Top dressing and incorporation of CRFs are the most popular methods
and are the general industry standards. A trial was conducted at the
Mid-Florida Research and Education Center in 2018 on strategic fertilizer
placements and their effects on weed growth and reproduction. The results
from this trial showed that the popular top dressing and incorporation
promote weed growth in comparison to subdressing and dibbling.
30 JANUARY 2021 GPNMAG.COM
THE TRIAL
One gallon plastic containers were filled with a substrate composed
of bagged pine bark mixed with sand at a 8:1 (pine bark:sand, v:v) ratio.
Dolomitic lime was incorporated into the pine bark/sand mixture to make
the pH approximately 5.5 at the time of filling the containers. Fertilizer
(Osmocote Plus micronutrients 17-5-11 [8 to 9 mo.], ICL Specialty
Fertilizers) was added to each container at 36.5 g (6.2 g N, 1.8 g P, 4.0 g K),
representing the manufacturer's recommended high rate, via incorporation,
topdressing, subdressing or dibbling. Incorporation of fertilizer was done
by thoroughly mixing fertilizer homogeneously throughout the substrate
before potting.
Figure 1. Four different types of controlled-released fertilizer placements in
container production.

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January 2021

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