More on Stalk Rot, Corn Dry Down

Clarke McGrath

A couple of big issues are staring us down; stalk rots and corn dry down. These issues are tied together and we may have some tough decisions to make. Artificial drying can certainly test a growers patience. As energy prices (especially LP) climb and/or availability of LP becomes an issue, costs can really add up. All this makes us appreciate any natural drying that Mother Nature can provide. This fall, leaving corn in the field to dry naturally for too long may be problematic in areas for a couple reasons;

-the stalk rot issues we discussed in the last blog have only gotten worse. In scouting, field visits and putting in cover crop plots I have spent a lot of time in corn fields recently with clients in their corn. Stalk rot and resultant standability issues are not hard to find. If you can scout your corn well and find areas that have good stalk quality, then some field drying may be in order. For fields with significant stalk rot and risk of lodging, the risk/reward tradeoff of field drying vs pulling it wet and artificial drying is worth a good look.

-unfortunately, this time of year risk (lodging) escalates and reward (natural field drying) typically decreases. We have had tough luck getting a lot of GDD’s for speeding along maturity and drying in the last month- around 20% below average- and as we head into October field drying usually slows even more. Some good news is that the 7-10 day forecast does show some above average temperatures, so if we can dodge the showers we’ll gain some ground.

A little bit on estimated field drying

I’m getting a lot of questions about how much, and how fast, our corn will dry in the field, especially as we head into October. A really good question, with a typical agronomic answer… it depends.
My understanding (some good info from Dr. Roger Elmore from UNL and previously 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 October as temperatures drop, we accumulate around 5-10 GDDs per day. Doing the math on all this… not pretty. From the few harvest reports, some hand shelling, and listening to very experienced growers as they chew on recently black layered corn (and when we double check their estimates with a grain moisture meter they are usually pretty darn close), there is a lot of corn sitting out there around 30%, so we’ll use that as an example.

30% corn this morning (26 Sept); looking through next Wednesday (1 Oct)- based on the forecast- we’ll accumulate approximately 120 GDD’s. The math tells us this will bring that 30% corn down to around 26%. Given the winds and the more “open” canopy in many fields as a result of the foliar leaf disease, experience leads me to think we’ll gain a little more ground than that so we’ll go with 25%.

25% corn starting 2 Oct and looking through 5 Oct, the forecast gives us around 42 GDD’s.

So our rough approximation puts us at around 23% or so as we start the week of 6 Oct. That’s not dry enough to make many of us very happy given the cost of drying (time and $$).

Then what?

If “average” conditions return for mid-October, recall we get around 5-10 GDD’s per day, and it takes approximately 45 GDD’s to drop a point from 25% on down… so we are projected to drop maybe couple points a week through mid-October. As we look towards averages in late October and into early November, we may drop a point a week, and if we head into mid to late November field drying often slows to a crawl.

So based on the above, today’s 30% corn might be around the 17-18% range by Halloween time. Or wetter… or drier…. It depends. We’re all no doubt on board with hoping for a warm, dry run that has us done before then and patiently waiting for fall NH3 season to start.

Remember all the above is “ballpark”; as mentioned earlier, a warm windy day like today (26 Sept) may pull more moisture than our GDD estimate since we have a nice breeze. On the other hand rainy, cloudy days may see less drying than the accumulated GDD’s would indicate.

Husk and ear characteristics will also affect dry down. Ears with the following will allow for faster drying: fewer and thinner husk leaves; early husk leaf senescence; ears with tips that protrude beyond the husks; looser husk leaves; early ear drop from an upright position; thinner or more permeable pericarp. Dr. Bob Nielsen at Purdue University has a more complete discussion here.

What about artificial drying? Here’s a bin full of information from our own
Shawn Shouse, Field Specialist-Ag Engr, Iowa State Univ. Extension and Outreach
This fall could potentially be another challenge for corn harvest, drying and storage. Here are some good resources for brushing up on your corn drying and management skills.

To compare the costs of drying options along with field dry-down, two new Ag Decision Maker (ISU) decision tools are posted with their September 2014 updates:

Estimating the Cost for Drying Corn

Source : iowafarmertoday