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Issue No. 22, Article 7/September 5, 2008

More Ear Oddities, and a Possible Cause

As an "Alert" two weeks ago, and in the previous article in this issue of the Bulletin, I reported on unfilled ear tips and blunt ears. I continue here the "odd ears" theme, with some additional information and observations.

Based on an indication from BASF that part of the problem with fungicide damage that we saw last year might be related to spray tank additives, I conducted a small experiment on late-planted corn here at Urbana. The hybrid Pioneer 34A20 was planted on June 11, at about 30,000 plants per acre. Treatments were applied on July 24, when the corn was in the V13-V14 stage and about 70 inches tall. Tasseling was about a week after treatment. I used 20 gallons per acre of spray solution.

Treatments included untreated check and nonionic surfactant (NIS) at the labeled rate of 0.25% and at 0.5% (2X). Headline fungicide at 6 oz per acre was applied by itself and with each of the two NIS rates. The final treatment was CoRoN foliar N by itself, at 4 gallons per acre.

There was little foliar disease present at the time of application, and there is little in the field at present. But the effort to reproduce damage similar to that we saw in 2007 was very successful. In plots with damage, symptoms ranged from slight ear size reduction and oddly angled ear shanks to complete loss of ears. Most common damage symptoms included the "bouquet" ears formed by small ears trying to develop from the same shank as the main ear. The following photos show such ears with and without husks. The main ears have few and scattered kernels, and the small ears developing on the same shank have few if any kernels.

Ear, without and without husk, affected by NIS.

On September 3 I estimated the percentage of the ears that were showing symptoms following the different treatments. Table 2 shows the percentages of ears affected. These data clearly show that most of the damage came from the NIS by itself, and that increasing the concentration increased the amount of damage. Headline fungicide by itself did no damage compared to the untreated check, but adding fungicide to the NIS increased the damage by about 10 percentage points. About 10% of the plants in the 0.5% NIS treatment had no ears at all, regardless of whether Headline was used. Few of the plants in the other treatments had missing ears.

I plan to take yields from these treatments, but it is clear that yield loss will be substantial and that NIS will be responsible for most of this loss. As the following photo shows, affected ears in all of the NIS-treated plots have few kernels developing. Adding Headline may have reduced kernel numbers even more, but with only one ear per treatment taken for the photograph, we need to be cautious about reaching any conclusions.

Ears following various pre-tassel applications of NIS, fungicide, and CoRoN.

I have no indication that damage from NIS is related to some of the other ear oddities and problems we have seen and heard about in 2008. But most fields are sprayed at some point with herbicide containing surfactants, and it could be that corn in 2008 was, due to how it developed, unusually sensitive to effects of surfactants. We can think of a surfactant as a detergent or liquid soap, with large molecules that can dissolve in water on one end and in oil on the other. Since molecules that make up membranes in cells have a similar structure, it is clear that surfactant that gets to cells can cause serious damage. How such large molecules would ever reach the plant cells that will make up the ear is not at all clear.

One of the more unusual cases of damage I have heard about this year is from John Obery, who is located in Woodford County near Metamora. As shown in the following photo, John has fields with ears that are small in diameter, with reduced row number near the base, but that have a restriction partway up the ear, with more row numbers above that, but with overall ear length shorter than normal. This problem is worse in one of his best fields, and there have been no weather-related problems in that area.

Ear oddity of unknown cause from a field in Woodford County. (Photo courtesy of John Obery)

This is a perplexing problem, and I have no idea what might have caused it. John reports that not all of his fields show this symptom. I would be interested to hear if anyone else has seen ears like this, and if anyone has ideas about possible causes.--Emerson Nafziger

Emerson Nafziger

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