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Extension > Local Extension Offices > Meeker > County Agriculture Educator > Articles > Soybean and Corn Update as Effected by the Cooler Weather in August

Soybean and Corn Update as Effected by the Cooler Weather in August

Source: Dave Nicolai, Extension Educator, Crops, UMN Extension

Soybean Aphid Update:
Bruce Potter, University of Minnesota Integrated Pest Management Specialist, Southwest Research and Outreach at Lamberton reports that soybean aphids are still present and reaching economic threshold levels in new areas. Yes, it is later in the cropping season however, if your soybeans have not yet reached full seed (less than the R6 stage) and have significant (1000s of aphids/plant), Bruce would not advise waiting for entomopathogenic fungi or other bio-controls to catch up.

We recommend that growers continue to use the 250 aphid/plant threshold through the R5 stage. While less common, significant and economic yield losses from very large, late developing, soybean aphid populations can still occur during R6. Giving up on an increasing aphid population during R5 can lead to unpleasant surprises in R6. Pre-harvest intervals (PHI) are now an increasingly important factor in insecticide decisions.

Corn Growing Degree Days: Lagging behind normal in 2017?
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 we use the 86/50 method (also called Modified GDD or Corn GDD) since it only allows GDD to be accumulated when temperature conditions are optimal for corn development (above 50°F but below 86°F).

Given the recent rains and cooler than normal day and night air temperatures, growers may have questions as to the pace of corn development and future harvest and grain drying questions for 2017. Farmers and the general public have access to an on-line tool from the Useful to Useable (U2U) web site now hosted on the Midwest Regional climate Center website which can be used to calculate growing degree dates, silking & black layer dates in corn as well as the probability of freezing dates.

The Corn Growing Degree Day (GDD) decision support tool puts current conditions into a 30-year historical perspective and offers trend projections (based on climatology) through the end of the calendar year. GDD projections, combined with analysis of historical comparison data, can help you make decisions about seasonal climate risks, activity planning, and marketing decisions. 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.

For example in Renville County, Minnesota as of Wednesday, August 23, the county on average has accumulated 1923 growing degree days compared to the average of 2079 GDD’s for a past 19 year average. The average date for corn black layer (physiological maturity) for the county is Sept 6 (2280 GDD’s). The on-line tool is currently projecting the 2017 corn black layer to occur on approximately September 24 for a 95-day relative maturity hybrid in the county. The average first fall freeze date for the county is October 9.


David Nicolai
Extension Educator, Crops & Institute for Ag Prof Coord
(651) 480-7706
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