| Arable
Dow Shield controls key competitive weeds in maize
When Dow Shield (clopyralid) was first registered in the UK in 1976, over 40 years ago, maize was an insignificant crop
in the UK and AD plants on farms were relatively unknown.
ith the
development of
maize varieties
that suit our
climate and the
need for another
break crop, maize has increased
its area with close to 200,000
hectares anticipated this year. This
growth may be for one of four
reasons - as a consequence of the
Three-Crop Rule or to spread the
workload or to introduce another
break crop on the farm in order to
get rid of difficult to control weeds
such as black-grass or to add to
energy production. The majority of
maize, according to the June
W
Census 2015, is fodder maize, but
there is an area of maize that is
grown for energy production in AD
plants. Last year 19% of the total
maize planted was grown for this
purpose – so nearly 1 in 5 fields
are destined for the AD plant now
and 4 in 5 are forage maize.
(81%).c
“When growing maize, yield is
the overriding consideration. But
maize is a weak plant during
establishment and maize
seedlings can be overwhelmed by
weed competition, especially by
those high biomass weeds that
grow quickly. Weeds colonise bare
open soil between the rows and
take advantage of the wide rows
and upright growth habit of the
maize crop. Early removal of
weeds such as thistles, sow
thistles and mayweeds is essential
to achieve yield. Crops are
generally sprayed two or three
times with a herbicide, pre and
early post-emergence, to ensure
the crop is able to grow through
this vulnerable early stage,” says
Peter Waite of Dow AgroSciences.
Dow Shield 400 was granted a
full label recommendation for
forage maize in 2012 and is a very
useful product to control high
biomass, highly competitive weeds
such as sow-thistle, mayweeds,
groundsel and corn marigold. It
can be applied post-emergence to
all varieties of forage maize at 0.25
l/ha from the 3 leaf stage up to the
9 true leaves of the crop. It shows
very good crop safety, despite its
post-em window.
“Maize forms the base
feedstock for most on-farm AD
plants, with yield being the key
driver. Growers, particularly new
growers, need to be aware that
when Dow Shield 400 is used in
maize destined for the anaerobic
digester, it takes 6 months for the
chemical to breakdown and so the
digestate should not be spread
onto susceptible crops. If the
digestate is spread onto grass,
cereals, oilseed rape or maize,
there are no worries. It is better to
be safe than sorry and follow the
advice on the label or ring the Dow
AgroSciences Hotline,” says Peter.
Obviously the majority growing
forage maize do not have to worry
about this specifically but do have
to follow the label.
“When growing maize, yield is
the overriding consideration.
But maize is a weak plant
during establishment and maize
seedlings can be overwhelmed
by weed competition, especially
by those high biomass weeds
that grow quickly”
The label text says ‘Dow Shield
400 residues in plant tissue
(including digestate) which have
not completely decayed may affect
succeeding susceptible crops. If
treated crop remains have not fully
decayed by the time of planting
following crops, avoid planting
peas, beans, other legumes,
carrots, potatoes, lettuce,
glasshouse and protected crops.
Winter beans and peas should not
be planted in the same year as
treatment. Where susceptible
crops are to be planted the
following spring, do not apply Dow
Shield 400 later than the end of
July of the previous season.’
Be aware, Peter says that other
herbicides, both pre-emergence
and post-emergence, used in
maize have following crops
restrictions. “Growers, especially
those new to the crop, need to
make sure they read the labels
thoroughly, so they are familiar
with any restrictions on following
crops.”
www.farmingmonthly.co.uk
May 2016 | Farming Monthly | 21