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Desember 2018
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Certified seed
– your first defence against
Sclerotinia
in soybeans
S
clerotinia
, a sporadic fungal disease affecting a wide range
of host plants, has had a substantial impact on soybean
production during the previous season. This fungus has
the potential to reduce soybean yields with up to 50%,
should conducive environmental conditions for the infection and
rapid development of the disease prevail during the growing period.
Unfortunately, by the time the first
Sclerotinia
symptoms are
observed, very little can be done to control this fungus. There-
fore, preventative management practices should be implemented
and applied to minimise the level of infection and further spread of
the disease.
Early symptoms
One of the early symptoms of
Sclerotinia
disease is the sudden
wilting of soybean plants. Leaves will turn greyish-green before
turning brown, curling up and eventually dying off. The fact that the
leaves do not drop immediately, makes it easier to distinguish in-
fected plants from healthy ones.
Symptoms will normally be visible within two to three weeks
after flowering has commenced in the crop, given that the right con-
ditions persisted, and infection has occurred.
Sclerotinia
can easily be distinguished from most other soybean
diseases by the presence of a white, cottony, mouldy growth and
hard, black sclerotia on the inside and outside of infected stems
and pods. The black sclerotia is the survival structure of
Sclerotinia
and can easily be spread during harvesting.
Favourable conditions
The fact that sclerotia can survive in the soil for a period of be-
tween four years to seven years, while awaiting favourable condi-
tions, makes it even more difficult to contain this disease. The most
favourable conditions for the fungi to develop occur during the flow-
ering stages, with high rainfall and cool temperatures of below 28˚C.
The development of the disease occurs primarily after the closing
of the leaf canopy, which promotes cool temperatures and creates
a humid micro climate around the stems of the plants. High soil
moisture as a result of rain or irrigation contributes significantly in
creating the favourable micro climate underneath the closed canopy.
Sclerotinia
spores and sclerotia are widely found across South Af-
rica. However, some management practices conducted by produc-
ers may contribute towards the build-up of these bodies in our soils.
When grain, which was harvested the previous season, is being
used as seed it may not have been subjected to testing for qual-
ity properties. Should the commercial production have been in-
fected with
Sclerotinia
, the sclerotia which was harvested together
with the grain then gets planted together with the farm-saved soy-
bean ‘seeds’.
There are different opinions on the reasons for the sudden in-
crease in
Sclerotinia
occurrence. Mr Whitey van Pletsen (production
manager of Agricol and chairman of SANSOR’s Seed Certification
Standing Committee), holds the opinion that the only effective way
to manage
Sclerotinia
is by following an integrated process of best
farming practices.
Insist on certified seed
Start by planting healthy, good quality certified seed. The fields on
which certified seeds are produced by seed companies, are subject
to regular inspections throughout the process of planting, produc-
tion, harvesting, cleaning and packaging.
Seed samples of registered seed lots are taken by authorised seed
samplers for various tests to be conducted. Field inspections, sam-
pling and quality testing must be done according to internationally
accepted, validated methods and procedures. Seed testing is impor-
tant to assess the quality of seed being marketed to producers.
Mr Kobus van Huyssteen (technical officer at SANSOR) explains
the thorough and lengthy process of seed certification, ‘Certified
seed must meet more and stricter requirements than other seed.
The process, with more than 90 control points, exercises control
from breeder seed, through pre-basic, basic and finally to certified
seed multiplications and aims specifically to guarantee varietal pu-
rity and varietal identity, as well as seed of good physical quality.’
ON FARM LEVEL
Sclerotinia
/ Conditions / Certified seed
Seed
HANLIE DU PLESSIS
for SANSOR
“
“
The most favourable
conditions for the
fungi to develop
occur during
the flowering
stages, with high
rainfall and cool
temperatures of
below 28ºC.