By Dave Nicolai, Extension Educator, Crops, UMN Extension
Minnesota corn and soybean crops continued to make steady progress this past week towards maturity but are still delayed compared to last year, and the five-year average, according to the USDA Minnesota Crop Progress and Condition Report released -Monday, Aug. 12.
Silked corn, at 96 percent, was eight days behind last year and three days behind the five-year average. Thirty percent of the corn crop has reached the dough stage, 10 days behind last year and eight days behind normal. Corn condition was rated at 56 percent good to excellent. Soybeans blooming reached 97 percent this week, three days behind last year and one day behind the average. Seventy-four percent of soybeans were setting pods, five days behind average. Soybean condition rated
59 -percent good to excellent, declining from the previous week.
Because of the delayed planting season, there has been concern over this year’s delayed corn growth stages and the potential impact of frost or wet fall weather conditions. The University of Minnesota South West Research and Outreach Center’s official weather station reports that, as of Aug. 12, there were 1,717 corn growing degree days accumulated since May 1, compared to a historic average of 1,795 growing degree days while precipitation was 14.15 inches compared to a historical average of 12.48 inches since May 1.
Growing Degree Days (GDD) are a measure of heat accumulation within a specified temperature range. GDD are important for agriculture since they can be directly related to plant growth and development stages. GDD are sometimes also called growing degree units (GDU), heat units, or thermal time. For the Corn GDD tool we use the 86/50 method since it only allows GDD to be accumulated when temperature conditions are optimal for corn development (above 50°F but below 86°F).
There is an on-line growing degree estimation tool which can be accessed by farmers and the public called “Useful to Usable” calculator tool at (https://mrcc.illinois.edu/U2U/gdd/) which can be used to estimate precise GDDs on a county and township level in 12 of the upper Midwest states. For example, the tool estimates in the Lamberton area that black layer or physiological maturity (2400 GDDs) of the corn crop will not occur until approximately Sept. 25, compared to a historical average of Sept. 18, for a 100-day relative maturity corn variety based on counting GDDs starting on May 1. The area’s first fall freeze average date is Oct. 9. However, the St. Cloud corn area maturity is estimated at Oct. 16 for black layer (2280 GDDs) in 95-day relative maturity corn, the average fall freeze for the area is Oct. 8.
This tool puts current conditions into a 30-year historical perspective and offers trend projections through the end of the calendar year. GDD projections, combined with analysis of historical analog data, can help you make decisions about:
• Climate Risk – Identify the likelihood of early and late frost/freezes.
• Activity Planning – Consider corn hybrid estimated physiological maturity requirements, along with GDD projections, when making seed-purchasing and other growing season decisions.
• Marketing – Look at historical and projected GDD when considering forward pricing and crop insurance purchases.
While this tool is not meant to be a crystal ball, data and information derived from the tool can be used to make helpful inferences about current conditions, especially when combined with personal experience and localized knowledge. On average, it takes approximately 55 to 60 days from corn pollination to black layer or physiological maturity which is still not dry enough for harvest or