Cornstalk rot issues are getting worse in some fields in Iowa as corn harvest moves through the first week of October. In some cases stalk rot and lodging is getting a lot worse. "Stalk rot and resulting corn standability challenges are not hard to find in most of southwest and west-central Iowa, and this issue is surfacing across much of the state," says Clarke McGrath, an Iowa State University Extension field agronomist located at Harlan in western Iowa. McGrath writes a monthly agronomy column in Wallaces Farmer magazine.
Let corn stand in the field a little longer or harvest it now?
"I don't want to start a worry-fest about stalk rot," he says. "There are some fields that are rock solid, no problems with stalk rot or lodging -- not yet anyway. On the other hand, I don't want to sell blue sky. I've been in more than a few fields where accidentally knocking one plant down led to a domino effect that took several more down with it. If you can take one last good look at how your different fields and hybrids are holding up, that would be a good thing to do. You just don't want a lot of unpleasant surprises if you are letting your corn stand longer in the field before harvesting it."
Letting corn stand in the field to let Mother Nature dry the grain on the stalk instead of harvesting corn wet and drying it in your bin can save you money on drying cost. "But you need to let the fields with the strong stalks stand the longest. Those with stalk rot and weak stalks need to be harvested first," notes McGrath.
Scout to see which of your fields have good stalk quality
If you scout your corn now and find areas that have good stalk quality, then some field drying may be a good plan this harvest season. For fields with significant stalk rot and risk of lodging, the risk/reward tradeoff of field drying versus harvesting the grain wet and artificial drying is worth a good look. Unfortunately, this time of year the risk of lodging escalates and reward of natural field drying typically decreases.
On the optimistic side of things, the weather forecast predicts good things for the first seven to 10 days of October. That is, average to above-average temperatures, little rainfall and light winds. Those are great conditions for harvest and field drying. "We also haven't seen propane prices this low for years, and supplies for drying grain look strong as long as transportation logistics hold up," says McGrath.
Make an estimate of potential for field drying your corn
ISU Extension field agronomists are getting a lot of questions about how much, and how fast, corn will dry in the field, especially as this year's crop heads into mid-October. "That's a good question, with a typical agronomic answer… it depends," says McGrath.
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Some research done a while back in Indiana illustrates your challenges this year. "Field drying rates are much lower for corn that matures in mid-September (like this year) versus our more typical late-August time frame," says McGrath. "The Purdue research in Indiana showed that average daily drydown rates will range from about 0.8% per day for grain that nears maturity in late August down to about 0.4% per day for grain that nears maturity in mid-to-late September. For many of us, unfortunately, this year our grain matured on the later end of that spectrum, so expected drying rates would be closer to a rate of 0.4% per day."
By mid-October the rate of corn dry-down in the field is less
As corn growers aptly point out, the major driver of field drying is the weather (heat, humidity and precipitation) so drying rates for any particular day can vary a lot. If you want a good ballpark average estimate for this time of year, McGrath suggests this one: You can expect corn in early October to dry down about 0.5% to 0.75% per day, and by mid-October we are probably looking at 0.33% to 0.5% per day. As we head into later October and November the rate will likely decrease to 0.25% or less."
Another timely question: Should you apply N in fall?
The shift to more "fall-like" temperatures has farmers thinking ahead; "Maybe I can apply some fall anhydrous ammonia while I'm held up waiting on trucks, waiting for grain drying, or other typical fall delays." Keep in mind the only form of nitrogen ISU agronomists recommend applying in the fall is anhydrous ammonia. And you need to wait until later in the fall when the soil gets cold enough and stays cold enough.
ISU's Clarke McGrath offers the following observations regarding fall nitrogen management. Having been present for recent conversations that growers were having with their fertilizer dealers ("I want this certain toolbar") and engaged in discussions about N-Serve and how much N to apply, growers are hoping for a good fall application season. Knowing that the window could be tight this fall, and again this spring given there is little to no room to store additional precipitation so it won't take much rainfall to stop anhydrous applications, they are anxious to get a jump on it.
Don't be fooled by temporary cold spells especially in early fall
The bottom line is that fall N applications shouldn't necessarily be targeted to start the first day that temperatures reach 50 degrees F; be sure that the trend is for sustained soil temperatures below 50 degrees and continued cooling. The dates when soils cool below 50 degrees vary considerably in various Iowa areas, from late October in northern Iowa to late November in southern Iowa.
"So don't be tripped up by temporary cold spells especially early in the fall," says McGrath. "Watch the six to 10 day weather forecast. A forecast for above average temperatures may signal soil warming that could mean we need to wait to start applying anhydrous. To help illustrate where we are at, I like to use the ISU NPKnowledge website that shows soil temperatures over the last several days, and has a link to the six to 10 day temperature forecasts to help dial in the right timing to start NH3 applications." Visit the site at extension.agron.iastate.edu/NPKnowledge/.