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Issue No. 20, Article 4/August 11, 2006

If You Still Haven't Checked Fields, It May Be Time

While about 70% of the Illinois corn and soybean crops are currently rated good or excellent, we have been getting a few reports that things might not be quite as good in some fields as we've thought. At the risk of repeating what every agronomist likes to harp on this time of year, it might be time to go into fields that you haven't visited yet. Even if we can't change things in most fields, we can always learn something.

One of the more puzzling reports from northern Illinois this week concerns the "beer can ear," a problem that is noted somewhere almost every year but usually when conditions were unfavorable at some point earlier in the season. I would, incidentally, like to rename this "short ear syndrome" (SES), in part because it is more descriptive, and in part because it does not hint so directly about what some agronomists might be doing during their downtime.

Corn ears affected by this problem look like something happened to stop the lengthening of the ear, probably back when it was only an inch or less in length, or about stage V8 or so. Ears often have the normal number of kernel rows, but they might be no more than 5 to 15 kernels in length. Husks are usually normal in length and appearance, and it's not uncommon for this problem to first be noted as late-season purpling of husks, which is an indication that sugars have no place to go in the plant.

After seeing the problem sporadically for more than 10 years, we are probably no closer to knowing the cause than we were when it was first noted. Proposed causes have ranged from virus to nutrient deficiency to cold temperatures to herbicide. But no one knows how to make this happen on demand, so there has been little progress in understanding it. The problem is rare enough that it may not attract much attention or funding in terms of research to look for a cause and a cure.

In the case reported this week, one producer has a number of hybrids that are affected to some degree. Planting was in the first week of May, and herbicides were applied during the hot weather of late May. While some hybrids and parts of fields have only scattered plants showing the symptom, other areas and hybrids are showing short ears on as many as a third of the plants. It's doubtful that such ears will produce more than a third of normal yields, so overall yields will be reduced more than we normally see with this problem. The fields in question are mostly irrigated, and there were no really cool temperatures during development, so it's hard to see weather-related stress as the major cause. Could herbicide application during high temperatures have had such an effect? We just don't know, though evidence to the contrary is that plants would have been only at stages V4 to V5 or so at that time and the ear would barely have started to differentiate, if at all.

I would encourage people to squeeze ears as they walk through fields to see if this problem might be more widespread than we think or hope it is. With little else to go on, we might want to pay extra attention to fields where glyphosate or other herbicides might have been applied during the high temperatures in late May. You might recall that some mild plant damage was noted earlier on corn treated with glyphosate at that same time. It was not clear then whether or not herbicide was involved, and it still isn't clear, but perhaps these fields should be checked again. Please let me know if any problems are noted with ear development.

There are a lot of eaten-off silks in many fields, and in some cases silks for the kernels on the tip of the ear might have been eaten off and pollination prevented. It has been dry enough, and certainly warm enough, in some areas to cause some mild to extensive kernel abortion. This is another reason to get out and check kernel development. Later in the week (August 11), the NASS will make its first estimate of corn yield, based on estimated kernel numbers per acre. Because pollination was timely and the weather has been warm to hot over the past month, such counts might be a little more accurate than they sometimes are. Still, the final size of kernels is not easy to guess accurately, leaving yield estimates subject to revision.

Soybean canopies are good to excessive, with some of the taller plants we have seen in recent years. While this is a good indication that roots are tapping soil water well, there is some concern that the crop will have difficulty retaining and filling the number of pods and seeds that it needs for good yields. Counting seeds and pods is tedious and not very rewarding, but it is a good idea to pull plants sideways to see if there are the four or more pods per node, and three or more seeds per pod, needed to set the stage for high yields.--Emerson Nafziger

Emerson Nafziger

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