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September 2018
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Effective weed strategies
in sorghum
T
he slow growth rate of sorghum and
the sensitivity of this crop to most
herbicides, present the greatest
challenges associated with effec
tive weed control in sorghum. Despite these
challenges, an effective weed management
strategy in sorghum is similar to the weed
management strategies of any crop and is
based on a few fundamental principles.
Correct identification of
problem weeds
Pigweed (
misbredies
), thorn apple (
olie
bome
), khaki weed (
kakiebos
), nutsedge
(
uintjies
), morning glory (
purperwinde
) and
cocklebur (
kankerroos
) are common weeds
found in sorghum fields in South Africa.
In the sorghum production areas of the
Highveld area, cosmos (
Photo 1
), common
couch (
gewone kweek
,
Photo 2
) as well as
fleabane (
vaalskraalhanse
,
Photo 3
), have
also been reported to be problematic – es
pecially under minimum tillage practices.
Johnson grass (
Photo 4
) remains one of the
most challenging grass species that has to
be managed in sorghum production.
As no single herbicide will be able to con
trol all of the weeds in a field effectively, it
is imperative to accurately identify the
whole weed spectrum in order to select
suitable herbicides. In specific cases it
might be necessary to use mixtures of com
patible herbicides to be able to control the
whole weed spectrum. Should control with
herbicides not be effective, alternative op
tions must be explored.
Chemical control
Pre-emergence herbicides
Grass weeds can be extremely difficult to
control post-emergence in sorghum produc
tion due to the lack of selective herbicides.
Therefore, sorghum producers rely heavily
on the use of registered, pre-emergence
herbicides (acetochlor, alachlor, metola
chlor, dimethenamid-P or s-metolachlor).
It is imperative to pre-treat sorghum seed
with a safener (fluxofenim; Concep
®
) to
protect the seed against the pre-emergence
application of s-metolachlor (as per the
Concep label). All pre-emergence herbicide
labels should, however, be consulted in this
regard as acetochlor, alachlor, metolachlor
and dimethenamid herbicide labels indicate
that the treatment of seed with a registered
safener such as Concep will provide protec
tion against crop injury.
Without the use of seed protectants, crop
injury such as poor emergence, whiplashing
of leaves and stunting can occur.
Focus
Integrated pest control
Dr Maryke Craven, Marlene van der Walt
and
Dr Jeanetta Saayman-du Toit,
ARC-Grain Crops, Potchefstroom
1: Cosmos.
2: Common couch.
3: Fleabane in a no-till field.
4: Johnson grass.
2
3
4
1