Forecasts that the US soybean crop would come in way ahead of official estimates has driven Chicago beans below $9 a bushel for the first time in six months.
The November soybean contract slumped 2.7% to $8.93 a bushel as of 17:00 GMT.
Chicago's near-term soybean lot has not fallen below $9 a bushel since March 30, and not closed there since March 12.
The slide followed data from Informa Economics, the analysis group, pegging the US crop at 3.38bn bushels, ahead of a US Department of Agriculture forecast by 138m bushels.
The figure is also higher than FCStone's estimate earlier this week of a 3.33bn-bushel crop.
Informa, in data ahead of fresh Washington estimates expected on October 9, added that it expected the US corn crop to come in at 13.13bn bushels, 173m bushels higher than current official expectations.
However, forecasts showing a freeze late week provided some support, limiting losses in December corn.
"Soybeans are down more than corn in part because they are now less vulnerable to cold temperatures than corn, being further along in maturity," Vic Lespinasse, marketwatcher at GrainAnalyst.com, said.
The contract, which had looked set for a winning week, stood 2.0% lower at $3.33 ¾ a bushel.
Wheat was dragged lower in the melee, with Statistics Canada data pegging Canada's wheat output at 24.5m tonnes, 100,000 tonnes higher than analysts' forecasts, adding bear pressure.
December wheat slipped 1.9% to $4.44 a bushel.
However, European contracts once again did better. Their relative strength was in part down to technical factors, as Euronext November contracts approached closing, French based analysis group Agritel said.
A dry spell in Europe is also raising concerns for newly-sown winter crops.
Paris milling wheat for November ended E0.75 higher at E123.00 a tonne, with London feed wheat for November finishing £0.25 higher at £98.50 a tonne.
Late on Friday, Reuters said that 63,000 tonnes of French wheat had been detained by Egyptian authorities after tests showed levels of bad seeds exceeded statutory levels.