In this issue..

Blackgrass
Banbury blackgrass
strategies:
● Cultivation and drilling techniques –
shallow versus deep tillage
● Spring cropping
● Cover crops
● Variable seed rates in spring barley
● Herbicidal control in OSR
● Impact of varying flufenacet rates on
pre-em control.
“It may look like you’re hardly doing
anything, but just moving the top two
inches is enough to encourage blackgrass
to germinate, while allowing the soil to
aggregate naturally.”
At Mollington, shallow tillage is done
with an on-farm-engineered version of the
tine and press-based Cousins Surface
cultivator.
Strong root growth is fundamental to
improving soil structure and something
that will be examined with cover crops
on the site to improve natural drainage.
“It’s easy to underestimate what roots will
do,” says Dick Neale.
Crops that produce a strong tap root,
such as legumes, oilseed rape, linseed,
mustard or tillage radish, are best at
penetrating deeper into the soil, but a
range of three to four species should be
sown to provide different rooting depths
and spread risk, he advises.
Spring cropping
Cover crops may have a role to play on
heavy land by drying soil to depth and
enabling spring cropping –– a key tool in
cultural blackgrass control. Two fields at
Mollington are in spring barley this season,
with a range of seed rates and drilling
systems being compared.
Spring barley will only help reduce
blackgrass if grown correctly, Dick Neale
insists. This means getting a good flush
of weeds prior to drilling, minimising
soil disturbance at drilling, and sowing
enough seeds to establish a crop that
outcompetes blackgrass and delivers
a decent yield.
“You must be realistic about how much
seed will be lost, especially when sowing
spring crops on heavy land. Yield is all
about seed numbers in barley.”
Dick Neale says 22,000 barley seeds/m 2
Spring barley will only help reduce blackgrass if
grown correctly and enough seeds are sown.
are required for a 10t/ha crop, which
based on 24-28 grains/ear, 915 ears/m 2
and three tillers per plant, equates to
310-320 established plants/m 2 . At a
seedbed survival of 70-75%, this means
sowing 450-500 seeds/m 2 . ■
Cultural “stacks” key to blackgrass control
“Stacking” cultural techniques is essential for
effective blackgrass control, according to
Hutchinsons’ Neil Watson. The concept is often
applied to complex herbicide mixes, but has
equal merit for the range of non-chemical
options in the blackgrass armoury, he says.
Delayed drilling, spring cropping, higher seed
rates, cover crops and cultivation techniques
can all help reduce blackgrass pressure, but
their impact is much greater when used in a
coordinated way and integrated with chemical
options, he says.
Attention often centres on “percentage
control” but Neil Watson believes more focus
must be given to plants that survive, as
blackgrass has an impressive ability to
compensate for lower populations by producing
more tillers (up to 60 per plant) and larger ears
typically containing at least 200 viable seeds
per head.
This was clearly shown last season, when
blackgrass tillered heavily and some ears were
almost double the average size of 10cm, he
notes. “In such cases there’s double the amount
of seed return too.
“You might achieve 90% control of plants,
but this is only equivalent to 45% control of
heads given the ability of surviving blackgrass to
compensate through tillering. From the very start
it’s an uphill struggle.”
Blackgrass should therefore be hit hard with
all available options to minimise seed return and
deplete the seed-bank as quickly as possible,
he adds.
Reducing numbers below 12 plants/m 2 allows
a static population to be maintained, however
research shows this amount can still result in a
5% yield loss, so a “zero-tolerance” approach
may be better long term.
Building the cultural stack
● Soil – Improve structure and drainage to
reduce waterlogging, improve crop growth,
and facilitate spring cropping on heavy
ground. Cover crops with different rooting
characteristics could play a key role.
● Cultivations – Only work the top 25-50mm
to keep blackgrass seed within a “kill zone”
and allow deeper seed to deplete naturally.
● Delay drilling – Maximise stale seedbeds
prior to sowing and drill after the main
autumn flush. But this is only effective if a
good flush of weeds can be established and
sprayed off. Beware of delayed germination in
high dormancy years such as 2016/17 and/or
when soil conditions remain very dry.
The impact of cultural techniques is much greater
when used in a coordinated way and integrated
with chemical options, says Neil Watson.
● Cropping – Use spring cropping as the
ultimate delayed drilling – spring barley
remains the most effective option. Maximise
stale seedbeds and non-selective herbicides
before spring drilling.
● Competition – Increase seed rates (up to
450-500/m 2 ) to compensate for likely lower
germination on heavy ground in spring and
ensure crop outcompetes blackgrass.
● Chemistry – Focus chemical control on
effective pre-emergence residual herbicides
aiming for 70-80% control.
● Monitor – Tailor decisions to individual field
and seasonal conditions. Give it time – there
is no quick fix.
crop production magazine arable extra march 2017 37