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Late Reproductive Stages of Corn and Yield Estimation
  • Even with the late start of the season, as of September 1, most corn acres across the territory are in the mid to late reproductive stages of development.
  • In some areas of the Corn Belt, high temperatures and dry conditions were prevalent during corn pollination.
  • Adequate temperatures and moisture throughout the rest of the season will help the crop reach maturity before the average first frost date.
  • Regardless, now is a good time to make yield checks which can be quick and simple with the updated FS Yield Estimator mobile app.

Most areas across the Midwest experienced drier and slightly warmer than normal conditions during corn pollination this season. However, weather outlooks for September predict temperatures near or slightly below average. With corn acres at or approaching the late reproductive stages, it is now a good time to review these stages briefly.

Dent Stage (R5) – Under optimum growing conditions, corn will normally start to develop depressions or dents in the kernel crowns about four to six weeks after silking. This is the “dent stage” (R5) and signals a rapid starch accumulation in the kernels.At this point, and for the next 20 days or so, a distinct line begins to form, starting at the crown of the kernel and progressively moving toward the tip.This is referred to as the kernel milk line.The milk line marks the division between the starchy part of the kernel and the softer, milky part of the kernel (Image 1 above) Literature indicates that total plant death at the beginning of the dent stage will reduce final yield about 40 percent. Total plant death at about half milk line will reduce yields about 12 percent. Note: Milk line in kernels is often used to schedule corn harvest for silage.

Physiological Maturity (R6) – Maximum accumulation of starch in the corn kernel marks physiological maturity, which normally occurs 8 or 9 weeks following silking. Black layer formation at the tip of the kernel follows rapidly (Image 2 above). At this point, the corn is more-or-less safe from frost or other stress factors, although physical damage can still greatly impact yields.Grain moisture at R6 usually will range from 25 to 40 percent.If the plant is still healthy, it will actively draw moisture from the ear and harvest moisture will be reached more rapidly. According to the literature, once corn has reached R6, roughly 0.5-0.75% moisture can be drawn out of the kernels per day. Issues with plant health, stalk damage, disease or other serious problems will slow the physiological removal of moisture from the ear and the grain will have to “air dry”.

Image 2. Black layer formation in corn kernel


Estimating Yields Before Harvest – Corn yield estimates have become rather simple with the help of apps like the FS Yield Estimator app (available in the Apple Store for IOS). Follow the following steps:

  • Simply measure out a 17.4 ft of row transect in several spots in a field. This measurement represents 1/1000th of an acre.
  • In each of these 17.4 ft of row transects, count the number of plants with an ear of corn and record that for your Plant Population.
  • The Kernels portion is the number of kernels per bushel at 56 lbs/bu, for which we typically use 90,000 kernels as an average.
  • Collect 3-5 ears in each of the transects where you recorded plant populations and count the number of rows around and the number of rows long and insert it into the app. It is always good to evaluate more ears as this will give you a more accurate reading of what yield the grower could expect.

Image 3.  FS Yield Estimator available in the Apple Store for IOS

CornStages_2_Yield Estimator Icon.JPG

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Late Reproductive Stages of Corn and Yield Estimation


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