How Much Time do we Need to Finish out 2011 Corn and Soybean Crops?

by Greg LaBarge, Fulton County

With Labor Day around the corner and some pretty green crops covering all but a few fields in the region, the question becomes how much more time do we need to finish out our corn and soybean crop? The short answer is we need about another 30-45 days to get the majority of the acres to physiological maturity. The last CORN newsletter provided some hope via Jim Noel that we could expect a normal frost date.

Dates in fall by which the chance of the first 32 degree F temperature will have occurred is 50%.

The graphic below shows historic dates for a 50% chance of first Temps below 32 degrees. Thus a normal frost date of 10/10 to 10/15 would be a good thing and November 1 would be even better.

The answer about where your fields are at is in the growth stage of the crop.  Staging is not a difficult as it sometimes seems and hopefully a couple of hints here will help you in a look at your fields and days to harvest.

Soybeans are generally in an R5 stage approaching R6. During the pod set and pod fill stages you want to focus on the top four nodes on the plant.

Soybean Late Reproductive Stages:

  • R3 is initial pods set and there will be a pod 3/16 of inch long at one of the four upper nodes on the plant.
  • R4 is full pod and one of the four upper nodes will have a 3/4 inch long pod  when this stage is reached.
  • R5 is beginning seed where a bean in one of the pods is 1/8 of an inch long at one of the four upper nodes or basically when the pod is a full size but the bean is not noticeable.
  • R6 is full seed where the green bean fully fills the pod cavity in one pod at one of the four upper nodes.
  • R7 is the next to last stage or beginning maturity. At this stage a mature pod at any node on the plant indicates this stage. Typically the middle of the stem has the most mature pods.
  • R8 is full maturity.
  • Note a field is considered at the given stage when more than 50% of the plants reach that stage.

To reach the R7 stage from the stages listed above requires approximately the following number of days.

Current Stage Number of Days to R7










10 days to R8


5-10 days to 15%

For Corn we also have the late reproductive stages to take a look at:

  • R3 is milk stage where the ear has the look of an ear of sweet corn.
  • R4 is the dough stage where the starch are solidifying.
  • R5 dent stage where the top of the kernel is depressed.
  • Between R5 and R6 is the half milk line stage. Where the starch line has moved half way down the kernel.
  • R6 black layer when a kernel is plucked off the ear and you see a black layer where the kernel was attached to the ear.

Corn stages are across the board due to the planting dates and hybrid maturity so it is hard to generalize.

The table below shows approximate days to R6.

Current Stage Number of Days to R6







Half milk line




The number of days are approximate and depend upon actual temperatures for the period. For those hybrids or varieties in the earlier stages it would be worthwhile to check progress a couple of times as we move further into fall.

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