Funds failed to come to Chicago's rescue on Monday, as they did in the last session, leaving crops at the mercy of fundamental data, which proved better for cocoa than for corn.
Sure, the dollar was on crops' side, continuing to come under pressure from last week's soft US jobs report, which stoked expectations that American interest rates would stay low for some time.
The euro climbed back to E1.4524 as of 20:00 GMT, nearly three cents above its low of last week. A weaker dollar is usually helpful to US assets such as crops, making them more affordable to foreign buyers.
But the funds which investors had expected to snap up grains failed to show up.
Index funds were supposed to be undertaking their annual rebalancing act, in which positions are adjusted back to base levels – meaning 2009's laggards such as grains get bought, while top performers such as sugar are sold.
That process, and the buying in anticipation of the buying, as it were, have proven quite some draw.
"On Friday, in the last five minutes of the trade, 8,000 corn contracts were purchased, 4,000 wheat, and 5,000 contracts of soybeans," broker US Commodities said.
"In the last nine trading days, 115,000 corn contracts have been purchased. Managed funds bought 24,000 contracts of corn last week and now hold 229,000 long positions.
"They bought 18,000 contracts of soybeans and now hold 88,000 long positions."
But on Monday, fund activity appeared to be largely on the disposals side, with them proving to be sellers of 4,000 corn contracts and 2,000 soybean lots with an hour or so of trading to go, according to Vic Lespinasse of GrainAnalyst.com.
And there were some fundamental reasons to be at least cautious – the prospect of a slew of US crop data on Tuesday – and maybe even bearish. One was the Chinese trade figures which, while cheering most markets by beating estimates, came with a hitch for soybeans.
Darrell Holaday at Country Futures said: "Data out of China was deemed bullish for oil and gold as it indicated large imports for the month of December. But the soybean number was a little disappointing."
Not that the data ended up doing that much either for oil, which eased 0.6% to $82.22 a barrel.
"The energy sector broke from higher levels early in the morning and that put a damper on any substantial grain buying," Mr Holaday said.
And that wasn't the only reason to get down on corn. Weekly export inspections were poor for the grain at 20.6m bushels
Meanwhile, Argentina's president, Cristina Fernandez de Kirchner, said that the country's corn exports would hit 9m tonnes in 2009-10, 1m tonnes more than Washington is banking on.
Chicago's March corn contract ended down 0.5 cents at $4.22 ½ a bushel, with March soybeans down 11.5 cents at $10.10 ¾ a bushel.
The soon-to-expire January lot fell 11.25 cents to $10.01 ¾ a bushel, after earlier falling below $10 a bushel for the first time in 2010.
Wheat was the place to be, adding 4 cents to $5.72 ½ a bushel for March delivery, despite the presence of huge global stocks.
"Wheat continues to amaze many traders with its strength," Mr Lespinasse said, adding that he suspected that US winter wheat acreage data due from Washington on Tuesday would be "bullish, perhaps very bullish, judging by the way wheat is acting"
"Otherwise it seems no one can come up with a good reason why wheat continues to be so strong."
The pattern was not, however, repeated in Paris, where the stronger euro held back the January contract, which closed down E1.75 at E126.50 a tonne, although the March lot closed unchanged at E133.75 a tonne.
Rapeseed eased E2.75 a tonne to E286.00, held back by a slide in palm oil too.
One area where index funds did appear to have made themselves felt was in sugar, which closed down 2.8% in New York at 26.75 cents per pound for March delivery.
London white sugar for March ended down 1.3% at $717.10 a tonne.
Sugar, as one of 2009's top performers, is on the negative side of the rebalancing process.
Cocoa, however, closed up $47 at $3,343 per tonne in New York and up £7 at £2,277 per tonne in London on expectations of a continuing slide in deliveries from plantations to ports in Ivory Coast, the world's biggest producer.