The photo below of a cornfield in north central Iowa was taken the first week of August. We’ve shown it to several agronomists, asking each for a “windshield diagnosis.” So far we don’t have an Agdia strip trial test for goss’s wilt, or local weather data.
August 7, 2018 — Opinions so far, based only on the photo, include some kind of disease, nitrogen starvation, a local freeze event, and even a snippy comment about the brand of seed corn as the likely suspect. It’s not one of our clients’ fields, so there’s no first-hand information available.
We checked weather records for the area and found that the lowest temperature since April was 44 degrees. This part of the field wasn’t a ponded area. The early die-down is similar to what we’ve sometimes seen in very late August or early September. Corn runs out of nutrients and diseases move in.
This area had about 14 inches of June-July rainfall, which was a common event across many counties in Iowa. We’ve encouraged foliar feeding as a means of making up for leached-out, denitrified nitrogen.
Whatever the reason, it’s the earliest we’ve seen such extensive die-down in Iowa in early August. Hopefully, further analysis can offer some clues that contribute to future management solutions that head off an issue like this.
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Update Aug. 8: One co-op agronomist phoned to say that the die-down look like a combination of early soil saturation that kept roots from penetrating, followed by rapid denitrification, then invasion of stalk rot or other fungal disease from the lower leaves upward.
Update Aug. 9: The comments below by crop consultant Bob Streit are relevant to the early die-down phenomena.
The Corn and Bean Crop Development — by Bob Streit
Last week’s 90 F temps pushed the corn crop faster thru the grain fill period than is best for depth of grain fill. In 2017 there were no hot days and nights in August to stress the crops. Everyone who understands crops recognizes and knows that driving past a field on a country blacktop at normal speed and seeing the plants 75% to 90% brown or bleached white by early August does not suggest plants that will maximize yield. This is not every field, but a substantial percent in the western half and northern one third of the state and enough to affect overall corn yields.
One causal factor had to be the heavy June rainfall that caused shallower than normal rooting and created a situation where nitrogen was lost. Inability of the drainage systems to move water off the fields and restore an aerobic root zone created an oxygen depleted environment that could have led to major N loss thru volatilization, leaching, or runoff. If most operators had a chance for a do-over they would likely have either used an N stabilizer of some sort, or one what was more effective in keeping the N in the ammonia or organic form. In farming there are no do-overs, but we can learn for next year’s crop. Be sure to ask what the method of each stabilizers’ actions is, and what it does for soil health.
I mentioned last week about my findings with a Minolta Spad meter in different fields. Any reading with this higher dollar instrument which are on a 1 to 80 scale (with 1 being the least green), being below 50 before full dent will lead to reduced yields. The fields that died last week were those with readings in the low 40s or high 30s. They were out of energy. I have heard from a few growers who spent the $249 on the At Leaf instruments are happy with how those instruments work.