Herbicide-Treated Mulches Effective Method Of Weed Control
COLUMBUS, Ohio
Mulches pretreated with her
bicides have been found to be
an effective method of weed
control on ornamental plants
grown in nursery or land
scape settings.
The results of an Ohio
State University study to
measure the productivity of
herbicide-treated mulches on
weed control and plant toxic
ity have shown that certain
organic mulches pretreated
with herbicides produced
near-perfect weed control
and showed minimal phyto
toxicity up to 130 days after
application.
Such results are beneficial
to landscape and nursery in
dustries since the efficacy of
pre-emergent herbicides
would be extended, reducing
the need for repeated chemi
cal applications over the
course of a growing season.
The research is being
funded by the Horticultural
Research Institute, the Ohio
Research Endowment, the
USD A and several nurseries
in the Dayton/Springfield
area.
Hannah Mathers, an Ohio
State University nursery and
landscape specialist, said the
pretreated mulches provided
better control than mulches
or herbicides applied directly
to the soil or plant and lasted
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longer than the normal 45-
day herbicide application.
“The mulches treated with
herbicides had a 1.5 fold in
crease over herbicide applica
tions by themselves and a 1.8
fold increase over mulches by
themselves,” said Mathers.
“That’s a pretty significant
result. There’s something
going on there where the two
together gives superior effi
cacy over mulches or chemi
cals alone.”
The researchers studied
the performance of seven or
ganic mulches (pine nuggets,
cypress, Douglas fir, hard
wood bark, rice hulls, cocoa
bean shells, and Penn Mulch
a recycled palletized paper
product) treated with two
herbicides (Surflan and Flu
mioxazin not yet regis
tered for ornamentals) on
various broad-leaved ever
greens, conifers and decidu
ous shrubs.
Weed control was given a
visual rating of zero to 10,
with a “10” providing perfect
weed control. Plant toxicity
was also ranked from zero to
10, with a zero indicating
perfect plant health. Herbi
cide was applied to a 15
square foot area of a single
layer of mulch using the same
field application rates re
quired in the nursery and
landscape industries.
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Based on the results, rice
hulls and hardwood bark
treated with either Surflan or
Flumioxazin provided the
best weed control with mini
mal toxicity to the plants.
“For example, at 45 days the
pretreated hardwood had a
perfect ‘lo’ in weed control
and a ‘2.l’ in phytotoxicity.
Anything below a ‘3’ for phy
totoxicity is considered com
mercially acceptable,” said
Mathers.
Other pretreated mulches,
like pine nuggets, also ap
peared to outshine the per
formance of stand-alone
mulches and herbicides. “A
half-rate of Surflan on pine
nuggets brought phytotoxi
city down lower than even
half of what would normally
be applied with a chemical by
itself,” said Mathers. “Pine
nuggets performed well with
Surflan providing almost as
effective weed control as
hardwood bark or rice hulls.”
Researchers speculate the
herbicides bind to the
mulches, creating a slow
release carrier that not only
improves upon weed control
and reduces plant toxicity,
but also produces a more en
vironmentally sound product
by reducing leaching.
“Most of the chemical that
is applied directly onto plants
leaches away because of its
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water solubility,” said Math
ers. “So much of it leaches
away through pots that you
may apply 100 percent of the
chemical but you have only
about 30 percent of the actual
chemical to do anything with.
The rest is just lost.” In the
landscape the chemical
leaches intp the environment
as run-off. In nursery pro
duction, lost chemicals are
the result of improper cali
bration and run-off from
plastic or gravel, which in
creases the need for multiple
applications.
Mathers and graduate stu
dents Luke Case and Nathan
Tuttle plan to study exactly
where the majority of the her
bicide that is applied to the
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the mulch, within the plant
soil or at the bottom of the
container.
“If we can scientifically
show that the chemicals are
binding to the mulches, then
we have a product that can be
applied to plants and we
won’t have to worry about
any leaching into water
sources,” said Mathers.
“Also, a product that can
give you weed control for a
whole season is a big deal to a
landscape maintenance com
pany. If you can guarantee
total weed control to your
customers, it makes you look
good and that’s good busi
ness.”
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