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.

It’s likely that this damage, given that it affected only some fields, was unusually severe in some cases, and came during a season with late-planted crops and unusual stretches of cool weather in mid-season, will not often repeat itself. We have seen it before, however, and it certainly makes sense to do what we can to lessen the chance of damage. The first thing is to not apply when wind speeds are too high. We need to be especially careful when using herbicides or other products that can damage corn at low concentrations in fields next to corn, especially when corn is between head-high and silking, and is downwind from fields being sprayed.

The other lesson that we can take from this is to perhaps check fields a little more carefully to try to find such problems before harvest. This wouldn’t have helped prevent this, but it could have provided clues to help prevent it next time.

Read the article from The Bulletin at University of Illinois.