US farms, many of which have struggled against drought for much of the year, may now find too much rain the biggest threat to crops, with excessive moisture blamed for a surprise decline in soybean condition.
The condition of US crops remains unusually strong, US Department of Agriculture data showed, with the proportion of corn rated "good" or "excellent" as of Sunday rising by one point to 76%.
That figure was in line in with investors' forecast, and with a 2010 reading which represents the best for the time of year on records going back to 1995.
However, the proportion of soybeans viewed as in good or excellent health eased one point to 73%, surprising investors who had expected an increased rating, and with the decline attributed to excessive damp in some areas.
"Persistent strong showers and heavy rain has produced scattered areas of flooding," Gail Martell at Martell Crop Projections said.
Indeed, in Mississippi, where the proportion rated in the top two grades fell by nine points to 61%, USDA scouts reported that "heavy rainfall" meant that crop "replants are inevitable on many acres".
In the north east of the state, another scout said that "flooding has about 20% of our crop devastated," adding there "probably will be a great deal of replanting", while further south it was reported that "almost daily rain for the past three weeks has damaged stands and caused major weed problems".
In Iowa, the top soybean producing state, where many areas received rains of more than six inches last week, the proportion of the oilseed crop rated good or excellent fell by 2 points, albeit to a still-high 79%.
In Illinois, another major soy producer, where rainfall was "above normal", the reading fell by 4 points to 72%.
The wheat crop in Illinois, a major producer of the soft red winter wheat traded in Chicago, deteriorated too, by 7 points to 59% good or excellent.
"Some deterioration is noted on soft red winter wheat in Illinois and Arkansas due to rainfall," Brian Henry at Benson Quinn Commodities said, adding that "very little change" was seen in the hard red winter wheat crop currently being harvests in the central and southern Plains.
The proportion of winter wheat rated good or excellent remained at 11% in Kansas, the top producing state, and at 5% in Oklahoma, where drought damage earlier in the season was particularly marked.
And, with further rain in the forecast, there is potential for corn yet to suffer, Mr Henry said, if saying that this was a "tough case" to make for now.
"Talk of too much moisture has been muted, but could attract more focus if the rain totals expected over the course of the next week in the northern Plains materialise," he said.
"Central and southern Minnesota seem to have bulls eye on it with 4-5 inches expected between now and the weekend."
The growing wetness in the US agricultural heartlands "may be linked to an emerging El Niño", Ms Martell said, noting forecasts from official US and Australian meteorologists of an at least 70% chance of the weather pattern developing.
"El Nino is a known rain-maker for the central US," she said.
"Heavy rainfall is predicted this week in the Midwest, where soggy field conditions have already developed.
"Warming temperatures would increase evaporation, but recurring strong showers would cause locally heavy rain."