Yield loss on the edge of fields in 2013
Another clue is the fact that most affected plants tended to be of normal height this year, and if stress had occurred in time to damage developing ears, plants would likely have been shortened at least to some extent.
The main reason for questioning weather-related stress as a cause for this problem is that we didn’t have stress conditions in late June and early July. July temperatures were below normal, with 12 days having high temperatures less than 80 degrees here at Champaign, only 5 days at or above 90, and the high temperature for the month of only 93 degrees.
There was little or no water stress until well into August. I believe it’s more likely that the unusually cool conditions somehow made corn plants more physiologically sensitive to whatever might have drifted into fields than it is that high temperatures and winds caused these symptoms by increasing stress.
In terms of timing, soybeans were planted even later than corn, and it’s very likely that the last applications on soybeans took place in July, in some cases when ear development was occurring and the plant was subject to damage like we saw. The fact that we saw damage in some cases where soybeans sprayed around this time were across the road or some distance away tells us that trying to pin down exactly when (and from where) this happened may be difficult.
What moved into fields to cause this damage is likewise not going to be easy to identify after the fact. Glyphosate is part of most late post applications on soybean, and scattered kernels are characteristic of glyphosate applied (off-label) in late vegetative stage, before tasseling. But many applications also contain other herbicides that can cause injury to corn, and we showed several years ago that even nonionic surfactant (NIS) by itself can shorten ears and cause substantial yield losses. So any of several products sprayed, under conditions windier than normal and to corn with ear formation underway and sensitive to damage, could have contributed.
One additional possibility is that aerial application of fungicide and insecticide, perhaps made to soybeans, might have moved into non-target fields and caused this damage. Based on what we saw several years ago, these products by themselves are unlikely to produce damage like this on corn. Adding NIS can make such applications capable of damaging corn, but adding NIS with corn fungicide generally is no longer on the label for pre-tassel applications, and most such applications made to soybeans were made later than this.
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