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4: Valsdraadwurmskade aan jong mieliesaailing.
5: Swartmieliekewerskade.
6: Die mieliewortelwurm.
4
5
6
Die skade wat die valsdraadwurms aan die stam van saailinge
aanrig, het ‘n gerafelde voorkoms (
Foto 4
) wat tot ‘n groot mate soos
dié van die swartmieliekewer (
Foto
5
) lyk.
Die mieliewortelwurm (
Foto 6
) is ‘n minder bekende plaag in Suid-
Afrika, maar is wel in verskeie provinsies geïdentifiseer. In Noord
wes Provinsie was daar ‘n geval waar tot 42% van die plante in die
landerye beskadig was. Saailinge en jong mielieplante kan so erg
beskadig word dat plantestand soveel soos 80% verminder en
oorplant oorweeg moet word.
Besmetting kom gewoonlik in kolle in die land voor. In jare met
goeie lentereën en ‘n droë periode wat volg, kan daar ‘n ernstige
uitbreek van hierdie plaag wees. Die sigbare skade van hierdie
plaag stem grootliks ooreen met dié van die swartmieliekewer en
valsdraadwurm.
Chemiese beheer, saadbehandelings en voorkomen
de maatreëls soos om lande skoon te hou van onkruid
en opslag, is die beste manier om grondinsekte te
beheer.
69
September 2018
‘n Kykie na insekplae
Atrazine based herbicides (for the control of
broadleaves) are also available as pre-emer
gence herbicides (alone or in combination
with e.g. s-metolachlor). If such a herbicide
is used, careful note must be taken of the
residual effect caused by the active ingre
dient. Atrazine containing herbicides often
have quite extensive waiting periods before
a follow-up crop such as sunflower can be
planted.
The application dosage of a pre-emergence
herbicide is dependent on the soil clay per
centage. Soils with a higher clay content
warrants a higher herbicide dosage. In the
case of pre-emergence herbicides, between
10 mm to 20 mm rain or irrigation is required
within four days after application for the
herbicide to be washed into the soil.
Post-emergence herbicides
In sorghum fields, broadleaf weeds can
be effectively controlled through the ap
plication of post-emergence herbicides.
To achieve optimal control, herbicide la
bels should be consulted to determine the
growth stage of the weed recommended at
application.
Typically, weeds between the two and four-
leaf stage are most effectively controlled.
Herbicides applied beyond the four-leaf
stage of the weed will result in poor to no
control. Irrespective of the crop, pre-emer
gence control remains the most effective
manner of weed control, because it elimi
nates early competition of the weed with
the crop and is critical for optimal crop yield.
When applying post-emergence herbicides,
label instructions regarding the dose re
quired must be followed to the letter. The
objective must be to control the weed with
out harming the crop. The capability of the
crop to come through such an application
unscathed depends on its capability to me
tabolise or detoxify the herbicide.
If the dosage applied is too high, the abil
ity of the crop to break the active ingredient
down will be compromised and crop injury
may occur. A dosage rate that is too low will
result in poor weed control and can aid the
weed in resistance build-up.
In the case of post-emergence herbicides,
a certain rain free period (up to eight hours
in some cases) is required in order for it to
be rain fast. If it rains within this prescribed
rain free period the herbicide will be washed
off and not be taken up by the weeds. Fur
thermore, weeds that are under drought
or heat stress will take up less herbicide,
which will result in reduced efficacy of the
herbicide. Producers are therefore urged
not to apply herbicides during these unfa
vourable conditions.
Adjuvants aids or modifies the active in
gredient in a herbicide so that the herbicide
can function optimally. Some herbicides al
ready contain these adjuvants in its product
mixture whilst others require the adding
of an adjuvant. However, not all adjuvants
are the same and only those listed on the
relevant herbicide label can be added. The
application of an adjuvant not listed on the
label could result in excessive dispersal of
the herbicide, which dilutes the active ingre
dient applied and/or shorten the evapora
tion period.
Cultivation practices and
crop rotation
The control of common couch, fleabane
and Johnson grass present in a sorghum
field requires careful planning. Glyphosate
as well as paraquat are often utilised in
their control, of which neither is registered
on sorghum. These weeds are accordingly
controlled before planting, or through crop
rotation with other crops on which these
herbicides are registered. In the case of
Johnson grass, two to three years of crop
rotation are required, before sorghum can
be planted again.
Producers are welcome to contact the weed
science section of ARC-Grain
Crops at 018 299 6100 with any
enquiries they might have.
Effective weed strategies in sorghum
FoCus
Integrated pest control