Consider These Factors When Evaluating Corn Dry-Down

Iowa still needs a warm pattern to stay around for a while, and we need a dry fall, say ISU agronomists.

Published on: Oct 4, 2013

Located at Harlan in western Iowa, Iowa State University Extension field agronomist Clarke McGrath notes -- "so, we planted late in 2013, which set us up for wet corn; we followed this with a hot, dry spell that sped things along at the wrong time, and the last couple weeks we've been all over the board with temperatures. Many farmers are wondering about dry down of the stressed corn, 'and I wish I had a rock solid answer'. There are slight differences in opinions on how much, and how fast, our corn will dry in the field, especially as we head into October," says McGrath.

He explains that "My understanding (and I get the best info from our own Dr. Roger Elmore at ISU) is this; estimating dry down rates can be considered in terms of Growing Degree Days, or GDDs. Generally, it takes around 30 GDDs to lower grain moisture each point from 30% down to 25%. Drying from 25% to 20% requires about 45 GDDs per point of moisture. In September we typically average about 10 to 15 GDDs per day; this year we averaged nearly 18 GDD's per day in September, putting us closer to where we want to be even with a late planted crop."

CHECK STALK STRENGTH: What about letting corn stand in the field to dry down this fall versus harvesting it wet and drying it artificially? The ability of the stalks to stay standing is a huge question mark this year. The extreme stress has set us up for some serious stalk quality issues. Some farmers are finding this out as they look at fields preharvest."
CHECK STALK STRENGTH: What about letting corn stand in the field to dry down this fall versus harvesting it wet and drying it artificially? The ability of the stalks to stay standing is a huge question mark this year. The extreme stress has set us up for some serious stalk quality issues. Some farmers are finding this out as they look at fields preharvest."

In October as temperatures drop, the rate drops to five to 10 GDDs per day.

However, both of these estimates are based on generalizations, and it is likely that some corn hybrids vary from this pattern of drydown, as hybrid factors impact drydown rates some, says McGrath.

We still need the warm pattern to stay around and we need a dry fall, too

Some past research evaluating corn drydown provides more insight on the effects of weather conditions on grain drying. During a warm, dry fall, grain moisture loss per day ranged from 0.76% to 0.92%. During a cool, wet fall, grain moisture loss per day ranged from 0.32% to 0.35%. "So, let's hope the warm pattern holds for the later planted corn," says McGrath.~~~PAGE_BREAK_HERE~~~

He adds, "For some fields we will have to deal with decisions about getting the dryers fired up rather than relying on the corn drying in the field. Standability is a huge wild card this year. The extreme stress we had this year set us up for some serious stalk quality issues, and we are hearing of a few reports of farmers finding this out as they look at fields preharvest, in fact two calls today about this very issue on a day where I thought soybeans would be the focus."

On a related note, off and on over the last decade or better we hear reports of "yield losses" from grain losing dry matter in the dry down process as it stands in the field. ISU's Roger Elmore and his team took a look at this a few years ago. Several hybrids were compared in three years with different drying environments each year. Grain weights, i.e. dry matter, were stable in all environments following maturity. Grain does not lose dry matter during in-field drydown (for more information on this, see the reference listed below).

As Roger Elmore says, "as grain dries in fields after reaching black layer, you should monitor individual fields and hybrids for grain moisture, stalk quality and ear retention. Schedule harvest based on these variables."

Reference: Regarding dry matter stability, click on "Corn grain yield and kernel weight stability after black layer" on ISU corn web page.

Chewy bean stems (Green Stem Syndrome) --  ISU wants samples, please pass along this message to growers and retailers:

Reports are trickling in about green stem syndrome, or GSS, in soybean fields, which is like rubbing salt in the 2013 bean crop wound. "Before we get into details of this disorder, we wanted to let you know that ISU's IPM program is doing an analysis to determine the most common causes of GSS," says McGrath. "If you are a farmer or crop consultant who has a field with any level of GSS, we would really like to include it in our analysis. Please contact Nate Bestor at bestor@iastate.edu, an ISU pest management specialist, to see how you can participate."