Disease and late-planted corn and soybeans

Do you have a feeling of déjà vu this year? Planting progress unrolled at a pace like we saw in 2013, which was well behind the 10-year average. Last year, frequent rains were the common culprit that kept most of you out of your fields for so long. 

This year's wet conditions partnered with unseasonable air temperatures. In turn, this slowed the rate at which your soil warmed to a favorable planting temperature.

Disease and late-planted corn and soybeans


Don’t let the late timing fool you, though. Air and soil temperatures can improve rapidly. In turn, your corn and soybean plants will grow even faster than normal.

To the naked eye, your crops might appear to have made up for the time lost earlier in the spring. The pace at which these plants grew, though, means they are prone to a unique combination of challenges. One of these is the increased likelihood of disease.

6 reasons disease is more likely in late-planted corn

It’s common knowledge to you that late-planted corn is more likely to display fungal disease symptoms. Not as well-known is why the corn is so much more susceptible to disease.

We identified the following reasons to help you better understand this phenomenon:
  1. When planting is late, warmer environmental conditions lead to faster disease growth.
  2. Faster fungal growth leads to more inoculum, increasing the odds of infections.
  3. Late-planted corn means plants are younger when the fungi are more active.
  4. Young plants are more vulnerable to infection than older, hardened plants.
  5. Warmer conditions lead to rapid tissue growth on the plants.
  6. Rapid tissue expansion leads to a thinner, waxy cuticle. This compromises the plant's first line of defense against infections.

Al Eberline and Matt Eberline, Iowa growers who apply Stratego YLD on their corn


Adam Couch, Indiana grower who uses Stratego YLD on his soybeans

Profit and fungicides in corn

Our agronomists replicated field trials to test yield response to fungicides applied in corn. We then ran models using the average yield response and average industry costs for product and application. We wanted to know as much as you do — does it pay to apply fungicides in corn?

In short, we found that fungicides are profitable even when corn prices are lower than where they were a year ago. Three years of trial data show at-tassel applications of Stratego® YLD fungicide

resulted in an average corn yield increase of 11.8 bu/A. At $4 corn, that translates into a profit of $22.11/A.*


Yield loss in late-planted soybeans

Like corn, late-planted soybeans can grow rapidly when conditions stabilize. This compromises the plants’ natural defenses.  

Late-season diseases aren’t usually a concern in soybeans because they tend to occur when plants are mature. Yet, late planting can affect timing of maturity. Later-maturing plants are more susceptible to
late-season disease.

Yield and profit with fungicides in soybeans

Of course, the bottom line comes down to a number of factors that are still unknown at the time of this writing, such as what kind of rain and temperatures will finish out the summer. What we do know is that application of Stratego YLD in soybeans can be as profitable as it is in corn. For the past several years, soybeans treated with an application of Stratego YLD at flowering averaged 3.25 bu/A more than untreated soybeans.** This means an additional profit of $16.41 for $10 soybeans.

*Assumes application of Stratego YLD in corn applied at tassel using industry average costs for product and aerial application.

**Assumes Stratego YLD in soybeans using industry average for product cost and assuming a tankmix with a planned application of herbicides or insecticide.

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The University of Illinois helps you identify corn diseases and treatments.


Penn State University describes soybean disease symptoms.

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