Central Valley Cooperative

With the rain and in some cases snowfall that we have received there has been some discussion regarding hybrids and when should there be a switch to an earlier day hybrid.

Below are two tables from 2000-2013 that show Growing Degree Units (GDU’s) with planting dates of May 10 and May 15 and frost dates of October 1 and September 20.

 

 

Data suggests that in an “Average year” we will get between 2400 and 2500 GDU’s per year with those planting dates and frost dates. (The average frost date for the Central Valley area from 2007 to 2013 is October 1. The September 20 date was used to offer an additional more conservative comparison.)

 

The take home message from the GDU data is we should be safe staying with our original plan on hybrids until May 20.

Another factor that comes into play when looking at GDU data and hybrid decisions is when planting after May 1^st corn plants require less GDU’s to reach R1 (tasseling/silking) and R6 (physiological maturity or black layer). For every day after May 1 corn plants need 6.8 GDU’s less to reach R6 than those planted prior to May 1. This phenomenon also reduces the GDU’s to reach R1 by 1.6 GDU per day.

For example if a hybrid planted prior to May 1 normally needs 2550 GDU’s to reach black layer, that same hybrid planted on May 15 would only need 2448 GDU’s to reach black layer.

 

6.8 GDU’s per Day X 15 Days = 102 GDU’s -2550 = 2448 GDU’s

 

When you think of the concept of less GDU’s needed to make it to R1 it makes sense in that in most cases, the same hybrid planted later tends to be taller than the earlier planting. The plant is racing to make up for lost time and will grow faster and taller. The plants main purpose is to reproduce, and it will speed up that process to produce as much viable seed as it can. One of the drawbacks with these later plantings is potentially weaker stalks and taller plants, which may increase the likelihood of standability later in the fall.

 

When making planting decisions, as an Agronomist, I advise growers to look at soil conditions and not the calendar when making tillage and planting decisions. A common practice is to keep the same corn hybrids that you planned on planting until May 15 then start looking at earlier day hybrids. At the present time, I would stick with the hybrids that you planned to plant with until May 20, unless you are working with hybrids that tend to hold their moisture in the fall, or if the hybrid is a 107 day length or more but is marketed as a 105 day length hybrid.

Why stick to the plan?

1. Yield- The hybrids you planned to plant are the highest yielding hybrids for your farm. The hybrids of today are like those of 20 years ago in that in most cases by planting a 103 day hybrid you are not going to be 10 points wetter than a 96 day.

2. Harvest issues- Your hybrid plan was set up so you could reduce the potential for harvest issues: Moisture, Standability, Storage and Transportation.

3. Supply-There are hybrids to choose from but they may not be your first choice.

Going back to the year 2000 with an average planting date of April 20, we accumulate on average 196.5 Growing Degree Units (GDU’s) from April 20 to May 15. If you use 18.5 GDU’s per day it takes 10.62 days to make up those 196.5 GDU’s. When you factor back in that you are generally warmer in May vs. April you are closer to a 5 to a maybe 7 day difference.

So the question is are you going to change all of your plans for a 5 or 7 day difference?