CHICAGO: Chicago Board of Trade (CBOT) corn futures firmed on Thursday on worries that dry conditions would drag down crop yields in parts of the US Midwest, traders said.

* CBOT September corn rose 4-1/2 cents to $4.11 per bushel and new-crop December corn closed up 4-1/4 cents at $4.18-1/4 a bushel. Buying accelerated as both contracts broke through technical resistance at their 100-day moving averages.

* Dry weather in parts of the eastern US Midwest elevated concerns about lower yields. Crop conditions are already sub par following excessive rains during spring planting.

* Traders are squaring positions ahead of next week's US Department of Agriculture (USDA) supply-and-demand report, which is expected to show a smaller crop and fewer planted acres.

* Corn prices were anchored by weak demand for US exports. The USDA reported export sales of US corn in the week ended Aug. 1 at 239,500 tonnes (old- and new-crop years combined), below a range of trade expectations.