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Special
Integrated pest control
81
September 2015
Effective weed control beneϐits
soybean plantations
T
o celebrate the 25th anniversary of the Protein Research
Foundation (PRF) a decision was made to host a Soybean
Symposium during July. Information regarding weed control
was shared with nearly 300 attendees of the two sympo-
iums held in Delmas and at NAMPO Park, ne r Bothaville.
In his introduction, Mr Andries Theron (vice-chairman: Grain SA)
mentioned that there has been tremendous growth in soybean pro-
duction in South Africa in the past 15 years; from only 134 000 ha
planted during the 2000/2001 season, increasing to 687 000 ha in the
2014/2015 season.
This means that the projection of reaching the 2 million ton mark by
2020 is well in reach of South African producers. Theron however
mentioned that a continual increase in hectares has to be sustained
or improved on an annual basis to reach this goal.
For the first time in 40 years more protein for animal feed has also
been produced locally than imported.
Yield-reducing influence of weeds
on the crop
Keynote speaker, Professor Stevan Knezevic, from the University
of Nebraska in the USA (who is a global expert on weed control),
focussed on the yield-reducing influence that weeds have on soy-
bean production.
In his extensive research he has studied the yield that is forfeited
when weed control is delayed. Research has shown that the critical
period of weed control is influenced by different cropping practices.
Two sets of treatments were discussed:
Keep it weedy up to a specific leaf stage.
Keep it weed free up to a specific leaf stage.
According to Knezevic, the critical period of weed control in soy-
beans proved to be between the V1 and R2 (end of flowering)
periods. The general rule of thumb is that there is a 2,5% loss in
soybeans for every leaf stage of delay. During a dry season the weed
removal can be done earlier and later in a very wet season.
Similar quantitative work has not yet been undertaken on soybean
production in South Africa and although US research results may
differ from what is applicable to South Africa due to a difference in
weed composition, the principles of weed control remain the same.
Soybean herbicides
Prof Charlie Reinhardt (dean: Villa Acad-
emy and extraordinary professor of Weed
Science at the University of Pretoria) is
a well-known expert in the field of weed
science in South Africa.
He discussed the spectrum of herbicides
that is available for soybeans, as well as
resistance that may develop in weeds and
how to deal with it. Reinhardt shared some
insights gained from his extensive know-
ledge of harmful weed excretions (allelo-
pathy) to give symposium attendees a bet-
ter picture of what is available in terms of
weed control and how obstacles can be
avoided. “Weed control is one of the most
vital practices requiring effective applica-
tion if we are to achieve significant growth in
soybean yields,” he said. He further stated
that to reach the 2020 projection, producers
will have to ensure that there are less than
ten weed plants per square meter.
He also encouraged producers not to be-
come dependent on one mechanisation
LOUISE KUNZ,
SA Graan/Grain
contributor
1: Prof Charlie Reinhardt, Dr Brian de Villiers, master of ceremonies Andries Theron, Prof Stevan
Knezevic and Cobus van Coller shared their knowledge of soya with attendees at the PRF Soya
Symposium at NAMPO Park.
2: Milne Bredenkamp and Brahm Greyling (producers from Bultfontein)
enjoy a cup of tea before the symposium.
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