AGRICULTURAL
When continuously planting glyphosate resistant crops,
the risk of developing glyphosate resistant weeds can be
significantly reduced by using a variety of herbicides that
control each weed species in your field and by adhering to
certain guidelines. In doing so, you will be able to apply a
specific course of action that suits the situation.
By Julias Ramohlabi
Senwes Manager Developing Farmers
P
hosphonic acids are non-
selective, broad spectrum,
post-emergence, systemic her-
bicides that are active on leaves
and other green parts of plants. It works
by disturbing various physiological and
biological processes in the plant.
The most important effect is that of
inhibition of aromatic amino acid syn-
thesis, which causes a chain reaction of
inhibiting other synthesis processes in the
plant. The most common symptoms of
the phosphonic acids are termination of
growth, chlorosis of the foliage, followed
by necrosis.
AN INNOVATIVE SOLUTION
Glyphosate has provided a revolutionary
means for providing broad spectrum
weed control in maize, soybeans and
other crops via insertion of a glyphosate
resistant gene in the seed.
Growers have widely embraced the
technology, because it provides conve-
nient, effective and economical weed con-
trol in maize and soybeans.
THE DOWN SIDE
Research has shown that intensive and
long-term exclusive use of glyphosate can
lead to the development of glyphosate
resistant weeds.
MANAGING THE PROBLEM
Integrated management practices can
Widespread popularity and use of
maize, soybeans and cotton with gly-
Glyphosate (N-(phosphonomethyl)
glycine) is a broad-spectrum systemic
herbicide used to kill weeds, especially
perennials. It is typically sprayed and
absorbed through the leaves of the
plant.
Initially patented and sold by Monsanto
Company in the 1970’s under the trade
name Roundup, its U.S. patent expired
in 2000.
phosate resistance makes it important By engineering and inserting a glypho
for preventing and managing the vars such as soybean, maize and cotton,
to adhere to the following guidelines sate resistant gene in the seed of culti-
resistance of weeds to herbicides. these cultivars greatly improve conven-
minimise this risk, whilst providing growers
with a more consistent and effective weed
control programme.
Until now, most instances of weed
resistance to glyphosate have occurred
when glyphosate is used continuously and
almost exclusively for ten or more years in
orchard and vineyard crops, no-till (a sys-
tem of crop production in which the soil is
disturbed as little as possible) burn down
and continuous planting of glyphosate
resistant soybean and soybean-cotton
rotations.
It is expected that many farmers will
choose to plant continuous glyphosate
resistant maize, soybeans and cotton in
the future. This practice can be effective-
ly and profitably utilised – but important
guidelines must be brought into account.
While the odds of developing glypho-
sate resistant weeds on your farm are
probably less than with most other her-
bicides, weed resistance is nevertheless
developing because of heavy reliance on
glyphosate.
Producers should bear in mind that
the fact that they are planting seed with a
glyphosate resistant gene does not mean
that glyphosate is the only herbicide that
may be used on the crop.
tional farmers' ability to control weeds,
since glyphosate can be sprayed on
fields without damaging the crop.
FACTORS THAT AFFECT EFFICACY
OF GLYPHOSATE
Glyphosate requires actively growing
green plant tissue to function. Application
to drought-stressed weeds or weeds with
little green foliage; weeds covered with
dust; weeds damaged by insects or disea
ses may result in reduced weed control.
Heavy rainfall or irrigation shortly after
application may require retreatment.
Tillage or mowing within 3 days following
application may reduce weed control.
It is not advisable to spray glyphosate
if conditions of thermal inversion exist, or
if wind direction and speed may cause
spray to drift onto adjacent-non target
areas.
REFERENCES
Basic weed science and principles of
chemical weed control by AVCASA
From Perdue University Extension bulle-
tin: facts about Glyphosate-resistant
weeds, Boerbom and Owen, Dec 2006
http://www2.dupont.com/production
agriculture /en US/products services/
herbicides
SENWES SCENARIO | WINTER 2018
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