In this issue..

The reasoning is simple, he says. The
cover crop (which has to be established by
Oct 1 under the Basic Payment Scheme
rules) allows a healthy population of
blackgrass to establish underneath
the canopy, depleting the seedbank,
▲
he explains. The main objective is to kill
this off and not stimulate further blackgrass
germination when drilling the following
spring crop.
“The idea is to collapse the canopy to
gain access to the blackgrass and other
weeds lurking underneath. You generally
need to burn off the cover about six weeks
before the planned drilling date, so to
establish a spring cereal crop you’ll
be looking at a glyphosate (2 l/ha plus
adjuvant, such as Companion Gold)
Diversity key to preventing glyphosate-resistant blackgrass
On the very day the news broke that bacterial
resistance to last-resort antibiotic, colistin, has
been detected in China, a cross-industry group
gathered at Harper Adams University, under the
auspices of the Soil and Water Management
Centre, to discuss the unthinkable –– the
possibility of glyphosate-resistant blackgrass.
It hasn’t happened yet but if we don’t
practice good stewardship then glyphosate
resistance, in some form or other, will appear
in the UK, believes Barrie Hunt of Monsanto.
A sobering thought, with glyphosate currently
forming the last chemical defence for UK
growers against herbicide-resistant blackgrass,
and there are more than 1.2 million ha with
some degree of blackgrass resistance in the UK.
Glyphosate resistance is already a major
problem in the United States, where the
whole-scale switch into transgenic crops
massively increased the selection pressure on
the once stalwart herbicide. Professor Thomas
Mueller, from University of Tennessee, outlined
their experience with glyphosate-resistant
weeds to illustrate how growers in the UK
can perhaps learn lessons and avoid fighting
a desperate rear-guard action.
“The uptake of Roundup Ready was huge in
the US. Farmers liked it because it was easy, it
worked and yields went up,” explained Thomas
Mueller. “Farms got bigger because timeliness
was no longer important and farmers no longer
cared about, or even understood, basic weed
control principles. Glyphosate alone captured
50% of the total herbicide market and we got
resistance.
“In the US, our driver weeds are Conyza
canadensis (Canadian fleabane) and Palmer
amaranth (pigweed) and resistance has spread
rapidly across states. The cost of herbicide
programmes has increased by 200-250% in
the effort to control them. Here in the UK, your
driver weed is blackgrass.”
In Tennessee, soil erosion is a big problem
and no-till is normal practice because of the
benefits it brings in terms of soil stabilisation,
structure and porosity. “Where we have
glyphosate resistance, some growers have
had to return to tillage, losing all the benefits
of the no-till regime. There’s also a renewed
awareness of the importance of the seed bank,
with some growers resorting to costly hand
weeding to reduce seed return.”
The parallels to the UK are obvious ––
herbicide resistance, a driver weed and reduced
tillage systems. Harper Adams visiting professor,
Dick Godwin, told the assembly that no-till is
seeing a resurgence in popularity in the UK
because of the significant operational and
cost benefits it offers to growers, as well as
improvements to soils and erosion.
“No-till also throws up some big challenges
to growers – one of which is the control of
grassweeds and weeds not controlled by
glyphosate,” he said, explaining that stale
seedbeds and a reliance on glyphosate is one
of the fundamentals in a no-till situation.
Agrii has been looking at the impact of
establishment systems on blackgrass control at
their Stow Longa site. “Given current financial
restraints, every farmer is looking to reduce
establishment costs,” said Andrew Richards
of Agrii.
“Every agronomist is seeing a reduction in
available chemistry and what we do have, in
many cases, has a reduced level of efficacy. We
need sustainable establishment systems that
perform under a range of conditions and we
need to think about the pressure we’re putting
glyphosate under.”
One of the results from the Agrii work that
challenges the beliefs of the most evangelical
of no-tillers, is that rotational ploughing can
bring useful cultural control of blackgrass. “If
ploughing is utilised in a year of high seed return
there are huge benefits in fully inverting the
soil in terms of blackgrass control. If shallow
cultivations are then employed, the majority of
blackgrass seed remains undisturbed at depth,”
said Andrew Richards.
But won’t ploughing lose all the benefits the
no-tillers have strived to obtain? It’s something
Dick Godwin believes we need to find out.
“Although ploughing is contrary to the no-till
religion, we need to find the answer to the
question, what is the effect of occasional
Experts lined up to sound warnings on glyphosate
resistance – (from L to R) Barrie Hunt, Dick
Godwin, no-till farmer Edward Bradley, Thomas
Mueller, Tim Chamen of CTF Europe, Andrew
Richards and Prof Shane Ward of SWMC.
ploughing in a no-till system?”
Barrie Hunt pointed to the new glyphosate
stewardship guidelines which highlight that
one of the high risk factors for developing
glyphosate resistance is ‘no cultivation’, as is
commonplace in the US. “Sustainable use of
glyphosate is business critical for UK growers
and, by using integrated programmes, we’ve a
chance of keeping resistance at bay for a few
years to come.”
It’s a message that’s being shouted from the
rooftops but some growers still want the
answer to resistant blackgrass to come in a
can, suggested some of the speakers. When
asked why we’re not getting new chemistry
coming through, Andrew Richards made a valid
point. “If we had something new, how long
would it last? We need to learn how to make
chemistry last longer and prevent it breaking
down to resistance by changing practices.
The efficacy of Atlantis has lasted less than
10 years.”
Diversity is the key to avoid falling into the
resistance trap, said Thomas Mueller. “Diversity
in the chemistry we use to control blackgrass,
diversity in our cropping and diversity in our
cultivation systems.”
Cultivation system Blackgrass ears/m 2
Min till, Claydon OSR, Claydon Oct, Claydon Sept, Claydon Sept 501
Plough, Claydon OSR, Claydon Oct, Claydon Sept, Claydon Sept 266
Claydon Oct, Plough OSR, Claydon Sept, Plough Oct, Plough Oct 1.3
Source: Agrii Cultivations Systems study 2010-2015. Blackgrass population in 3rd wheat Edgar, 2015
20 crop production magazine december 2015