Concerns in the western Corn Belt over a cool start to the month of September were offset last week by much warmer than normal temperatures with highs in the upper 80s and low 90s, according to Planalytics, a business weather forecasting firm.

Crops in Iowa, Nebraska, Minn­­esota and South Dakota, which collectively account for 44 percent of total U.S. corn acres and 36 percent of soybeans, were considerably behind normal in crop maturity, according to the USDA’s Sept. 18 crop progress report. In Iowa, 30 percent of corn had reached maturity, six days behind average.

Planalytics’ latest satellite biomass “greenness” map shows that crops in northwest Iowa were considerably...