U.S. grain markets traded mixed on Sept. 29, 2026, as corn futures slipped, soybeans advanced and wheat contracts diverged while traders positioned for the USDA's quarterly Grain Stocks report. The report will provide new estimates of corn, soybean and wheat inventories as of Sept. 1. The numbers matter because they could reshape U.S. supply expectations, commodity prices and marketing decisions just as the fall harvest accelerates across the Midwest, influencing farmers, elevators, co-ops, livestock operations and other major grain users.

Weather is adding another layer of uncertainty as combines move through U.S. fields. Forecasts call for 2 to 3 inches of rain or more in parts of the Plains and Midwest between Wednesday and Saturday, with Texas, Oklahoma, Kansas, Iowa and northern Illinois among the areas expected to receive the heaviest totals. Those rains could temporarily slow fieldwork and grain movement through the supply chain. Conditions are then expected to turn drier than normal across much of the Corn Belt from Oct. 6-12, while above-normal temperatures are projected across the western half of the country.

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Corn futures briefly moved higher before technical selling erased those gains. December corn ended 1 cent lower at $5.22 per bushel, while March futures slipped half a cent to $5.36. The intraday market action showed a volatile session, including an early decline, a sharp recovery and renewed pressure later in the day. Crop conditions were unchanged, with 57% of U.S. corn rated good to excellent, 26% rated fair and the remaining 17% rated poor or very poor. Pennsylvania, Iowa and Minnesota posted some of the strongest combined good-to-excellent ratings among major production states.

Corn harvest and stocks set the stage for USDA report

The crop is also nearing the end of its physiological development. About 96% of corn is dented, slightly ahead of the five-year average of 95%, while 72% is mature versus the 71% average. Harvest reached 18%, matching the five-year pace but landing at the bottom of analysts' 18%-21% range. The larger market question is supply: analysts expect USDA to report 1.911 billion bushels of corn stocks as of Sept. 1, compared with 1.551 billion bushels a year earlier. That would represent an increase of roughly 360 million bushels and could influence basis levels, storage decisions and producer marketing strategies.

Soybeans moved in the opposite direction as a slower-than-expected harvest and technical buying supported prices. November futures climbed 9.5 cents to $12.9775 per bushel, while January gained 9.75 cents to $13.1275. Futures trended higher through much of the session before pulling back from the intraday peak. Elsewhere in the soy complex, December soybean meal eased 0.11%, while December soybean oil gained more than 1%, highlighting divergent price signals across products that matter to crushers, livestock producers and renewable fuel markets.

Soybean crop ratings were steady, with 58% rated good to excellent, 29% fair and 13% poor or very poor. About 75% of the crop was dropping leaves, matching the five-year average, while harvest reached 17%. Although that harvest figure also matches the historical average, it fell short of analysts' expectations of 18%-23%. The slower pace provided some support to futures ahead of the USDA report. Analysts expect Sept. 1 soybean inventories of 321 million bushels, down 4 million bushels from a year earlier, reinforcing expectations that domestic supplies remain comparatively tight.

Wheat prices diverge as planting trails the five-year average

Wheat markets delivered a mixed performance. December Chicago soft red winter wheat gained 4 cents to $6.9275 per bushel, while December Kansas City hard red winter wheat fell 2.75 cents to $7.43. Chicago wheat staged a pronounced recovery during the latter part of the session. Meanwhile, winter wheat planting improved sharply, rising from 17% a week earlier to 27% as of Sept. 27, but progress remained behind both last year's 32% pace and the five-year average of 34%. Eight percent of the crop had emerged, up from 2% the previous week.

Soybean and wheat indicators ahead of Grain Stocks

Analysts expect USDA to report 1.857 billion bushels of wheat stocks, a year-over-year decline of 277 million bushels. International demand is another factor for the U.S. wheat market: South Korea issued a tender for 3.7 million bushels of U.S. wheat, with likely shipment in November and December. At the same time, European Union wheat exports for the 2026/27 marketing year reached 250.2 million bushels through Sept. 27, while EU production estimates held at 4.564 billion bushels. Domestic inventories, export demand and global competition are therefore converging as key price drivers.

All eyes now turn to USDA's Grain Stocks report, with corn, soybean and wheat inventories capable of setting the next direction for grain prices. The report arrives as corn and soybean harvests move forward across the Midwest and another round of rain threatens to interrupt fieldwork. With corn stocks expected to rise year over year while soybean and wheat supplies are projected to tighten, any surprise in Wednesday's numbers could quickly reshape futures, basis levels and the market's view of U.S. grain supplies heading deeper into harvest.