The deterioration in South America's weather, which has already sparked downgrades to hopes for Argentina's soybean crop, is beginning to raise doubts of Brazil's too, dashing expectations of bumper yields.
The wet weather in central Brazil, including in Mato Grosso, has until to now been seen as an impediment to harvest progress and logistics, but a support to yields.
Indeed, upgrades to estimates for Brazil's 202-13 soybean crop have to some extent balanced downgrades to thinking on Argentina's, which is being sapped by hot and dry weather.
Informa on Friday raised its estimate for Brazil's soybean harvest by 1.1m tonnes, to 84.0m tonnes, but cuts its forecast for Argentina's by 3.9m tonnes to 54.5m tonnes.
However, on Monday, Brazil-based AgRural called time on rising hopes for Brazilian soybeans, lowering its estimate for the crop by 1.0m tonnes to 81.2m tonnes, warning that the heavy rains had begun to hurt yields too.
"Due to humidity, the quality of the beans harvested up until now has been below expectations," the consultancy said.
The comments were echoed by Michael Cordonnier, the influential crop scout, who warned of "more and more reports of poor seed quality" from the early harvest.
"We are talking about small, shrivelled seed, some is mouldy, with light weight, on which farmers are being forced to take discounts" to sell, Dr Cordonnier said.
"In few cases, seed has sprouted in the pod. When that happens the field is toast, and you might as well plough it in."
The results bore out a strategy among Brazilian farmers of splitting soybean sowings equally between early, medium and late maturing varieties.
"You not want all your soybeans maturing in mid-January because that is the height of the rainy season, and it might be two or three weeks before you can get the crop harvested," Dr Cordonnier said.
"They were talking about a super-record harvest in Mato Grosso. Now they just hope the weather dries up so they can get an average yield."
Meanwhile, further south, in Rio Grande do Sul, where dryness has tested crops, weekend rains had disappointed.
Dr Cordonnier said he was sticking by a forecast of 81m tonnes for Brazil's soybean crop, which would still be a record.
"I had been considering raising my forecast. But I'm glad I didn't," he said.
However, he did lower by 1m tonnes to 51m tonnes his forecast for Argentina's soybean crop.
The US Department of Agriculture, whose data set global benchmarks, pegs the harvest at 54m tonnes.
However, a report from its Buenos Aires bureau overnight estimated the crop at 53m tonnes, warning that "since mid-December, it has been hot, dry, and there hasn't been significant rainfall in much of the major production area".