Crops in the US were not expected to have deteriorated yet.
Investors had expected, at worst, a 1% decline in the proportion of
However, the US Department of Agriculture's weekly crop condition report showed a two-point slide, to 64% in the proportion of soybeans rated in the top two bands, and three-point slip to 66% in the number for corn.
"The percentage of the corn crop rated good or excellent fell for the top five producing states, and this is before the heat hitting the Midwest this week," analysts at Australia & New Zealand Bank said.
"If the current deterioration in crop conditions continues over the next fortnight, the ability for the US to produce a 'trend' yield for the corn crop looks increasingly questionable."
At Commonwealth Bank of Australia, Luke Mathews said: "US corn crop conditions deteriorated markedly last week. And only 35% of the crop is skilling, behind the normal pace of 47%.
"Crop concerns may support values today, particularly given hot weather forecasts."
And the weather outlook remains poor, from a grower's perspective, with a cold front for later this week expected to stay north of the eastern Corn Belt, and hot weather heading into August still on the agenda.
US corn crop conditions deteriorated markedly last week – 66% of the crop is now rated good‑to‑excellent compared to 69% the week prior. And only 35% of the crop is skilling, behind the normal pace of 47%. Crop concerns may support values today, particularly given hot weather forecasts.
Official US meteorologists foresee "large areas of above-normal temperatures covering all of the Rockies, all of Plains regions, all of the Midwest, the deep South and North East" over the eight-to-14 day timespan, WxRisk.com noted.
"Embedded in that region is an area of much-above-normal temperatures over all of the central and lower Plains, all of the Midwest into the North East and all of the deep South."
Below-normal rainfall is expected over western Texas, western and central Oklahoma, all of Kansas, Nebraska, South Dakota, Iowa and Missouri over this period.
OK, as many brokers have noted, there is little confidence around in further-ahead weather models which, after all, repeatedly forecast rain for drought-beset Plains winter wheat in the spring, only for the precipitation never to arrive.
"Given the uncertainty in the extended forecast, it seems the market doesn't have a big appetite for additional risk at this point," Brian Henry, at Benson Quinn Commodities, said.
"Expect the trade to continue to favour carrying a little bit of length, as opposed to creating new speculative short positions. But the market is going to have to push above the recent highs on its next opportunity to sustain the current upward momentum."
The near-term September corn contract made progress towards last week's highs, rising 1.3% to $7.05 a bushel as of 07:50 GMT (08:50 UK time).
The better-traded December lot gained 1.3% to $6.98 a bushel.
That helped fellow grain
Spring wheat added 1.0% to $8.31 a bushel in Minneapolis for September delivery, despite this being one crop which held its condition in the overnight USDA crop report, with 73% rated in good or excellent health.
Soybeans were the least enthusiastic, continuing a recent pattern of less volatility than the grains, adding 0.3% to $13.90 a bushel for August, and the same rise to the same price for the best-traded November lot.
The condition of the US cotton crop was actually stable, at a miserable 28% good or excellent.
But the fibre gained some support from higher prices on the Zhengzhou exchange, where the best-traded January lot added 0.5%. China is the top cotton producer, importer and consumer.
Furthermore, there were signs of a lessening in the macroeconomic fears which gripped markets in the last session, and to which cotton, as a non-food commodity and an item more dependent on discretionary spending, can be more susceptible.