Corn Maturity Race Tightens-up
  During August

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As of August 1st, it appeared that the majority of corn would have no problem reaching physiological maturity before our average first frost date of October 4th. Corn fields throughout the area had beat the first benchmark of being silked by the beginning of August. All of that has changed during the past month when we saw record low sales of sunblock and some folks no doubt contemplating tapping the maples for a rare summer sap run. As the calendars are turned to September, we find ourselves about 200 GDD's below normal for the growing season.

The next corn benchmark is to be dented by Labor Day in order to be reasonably sure that the "black layer" stage is reached by the average first frost date. Let's take a closer look at where we stand in terms of corn maturity.

We need a "miracle" September Table 1 shows the average GDD's accumulated from August 30 to October 4 in Fond du Lac County. In total, expect 420 GDD's to come our way during this time period. Add on another 30 if we can stretch that first frost date to October 11. Note that the average GDD's per day decreases from 15 to 4 from the beginning of September to October 11. What's needed for mature corn? Although there are several factors that influence a corn plant's progression through maturity, the major driving forces are heat and day length. The relationship between growing degree days (heat unit accumulation) and corn maturity is well documented. For our maturity zone, it takes corn about 1100 GDD's to progress from silking to physiological maturity (Table 2). Two management factors that may influence the actual number of GDD's needed for corn to mature are planting date and, to a lesser degree, hybrid maturity. Late-planted corn will usually require about 60 to 80 fewer GDD's than early planted corn progressing from silking to physiological maturity (black layer). Using Tables 1 and 2, we can at least make an educated guess as to whether a particular corn field will have any chance of making grain before the date of our average killing frost (Oct. 4). This analysis is presented in Table 3. Both full dent (½ to 3/4 milkline) and physiological maturity predictions are given. At full dent, agronomists generally consider that 90 to 95% of the maximum grain yield is made. However, corn frozen at this stage will likely have below normal test weights. Corn that likely won't make it to a "strong" dent stage probably should be earmarked for silage use either for yourself or a neighbor who can utilize forage. These arrangements need to be made now ---- not November. The race is on!