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By Staff | Jul 29, 2016

As the end of July approaches we recognize that the month that determines corn yields is just around the corner followed by the month that determines soybean yields.

The prospect for corn yields likely got a boost over the last 10 days with the multiple and measureable showers that marched across much of the Midwest.

Without them there would have been many acres that were walking on the edge of being in a very moisture-stressed situation.

Now we can rest easy at the expense of seeing grain prices march lower as the specs move out of the grain market to chase another rabbit.

As monumental as the weather and grain markets are for the Midwest and its grain producers, watching the tape delay proceedings of the RNC and DNC is proving interesting.

We thought the FBI hearings ended on a bad note.

However, it took a keen observer to recognize that international hackers and the Wiki-leaks group bent on revenge to really throw things into turmoil. It’s anyone’s guess as to how this will turn out as such events have never played out before.

The crops

A week ago several of us were closely looking at different corn fields that seemed to be changing slightly in color. Was it just the way the sun was reflecting or was it really something that was going health-wise or physiologically in those fields?

It has happened more in recent years beginning in mid- to late-July so it really is no surprise. Hopefully enough acres were managed well enough to meet the crop fertility and plant health needs that your fields remain among the “staying green” category.

Is the yellowing due to lost nitrogen or are the plants reacting negatively to the stressed placed against them?

There were definitely more acres that received late season N applications using the Y-drops as well as dry application of urea via tall-tired applicators. Being frugal and seeking to be most among the most efficient N users is now in.


It is the normal time when different small six- or eight-legged pests begin to show up in our fields. By July 20 we have often seen high levels of aphids feeding in soybean fields.

So far the numbers remain light. It is still worth scouting for them and be alert to any increase in populations to the north and west as they normally spread via breezes from those locales.

One small pest that did surprise me a little were the spider mite populations that have showed up in bean fields that were under moisture stress. With the drought conditions being eliminated to a great degree the fungus that normally parasitize them should make them disappear.

Another insect worth paying attention to this July and August could be the European corn borer. Though we saw little trace of the first generation there were fields planted to non-Bt hybrids that showed measurable – and in places treatable – levels of the tunneling pests.

Their appearance was two to three weeks ahead of schedule. If the rest of the summer remains warm does that suggest we may see a partial third brood this season in southern Iowa?


While the recent rains were absolutely necessary the wetter conditions have increased the humidity levels in both corn and bean fields. This will increase the chances of seeing treatable levels of diseases in both.

Before you do spray it is best to identify each disease that is present, gauge the level of incidence, and compare what you find to your calculated treated thresholds.

In beans the time to spray for septoria, downey mildew and other diseases is typically at or near R3, which is typically now and just as 30-inch rows close.

In corn the usual fungal diseases that can be spotted this week are common rust, gray leaf spot, Northern corn leaf blight and physoderma leaf and stalk infections.

Whether any or all of these reach their ET will depend on varietal characteristics, mineral levels in the plants and weather variables through the next six to eight weeks.

In other words stay alert to leaf diseases in both crops, identify those that appear and be able to make treatment decisions about any that have proven troublesome in past seasons.

Bob Streit is an independent crop consultant and columnist for Farm News. He can be reached at (515) 709-0143.

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