Weather
The weather in 2016 set up the potential for some very high soybean yields in many areas of Illinois and to be honest, some have reported the highest soybean yields they have ever had on their farms. But, the weather could have led to yield variability and some problems that I have termed “www”.

Weeds
The number one issue that occurred this year appeared to be weed competition. With some growers planting earlier than ever in cool conditions, some questioned if burndown applications would work if weeds were not actively growing. Heavy rains and cool temperatures in open canopies were the “perfect storm” for waterhemp.

Were pre-herbicides used or were residuals leached away by rain? Could the weeds have been too tall at post spraying or were there too many late flushes of weeds? Was the waterhemp in your field resistant to glyphosate (group 9) and PPO (group 14) herbicides? Although not overabundant, some stem borers (Dectes) were found in weeds such as cocklebur and giant ragweed, which interfered with herbicide uptake. In areas where weedy hosts were found, these stem borers sometimes moved to soybeans.

The waterhemp in this field located near Owaneco, IL, was confirmed to be resistant to glyphosate (group 9) and PPOs (group 14) herbicides by the U of I Plant Clinic.

What Went Wrong?
The most critical time for yield loss to occur is during podfill (R3 – R5), and factors that could cause stress are drought, excess heat, disease, insects, fertility, hail, lodging and SCN. Many questioned if they should apply a fungicide this year and in many cases this paid off, especially in early planted or varieties that were susceptible to foliar fungal disease.

Our indeterminate soybean varieties were taller than ever, especially if the variety was tall, planted early, into high fertility soil, with a high population or had a low standibility score. The most detrimental factor to affect yield can occur if soybeans lodge at the beginning of seedfill, when seeds start to increase in size. If you planted after Mother’s Day, and then decided to replant, higher than expected population could have resulted. This could have encouraged diseases under the lodged canopy such as white mold in Northern and Central Illinois.

In early August sudden death syndrome (SDS) appeared in the Northern portion of Illinois, as well as in some areas of Central Illinois, in early planted soybeans, especially in fields with compaction or poor drainage. We saw the seed treatment ILeVO^® promote plant health as well as provide yield responses. The other disease that I found from time to time, that could have been confused with SDS, was stem canker, which is part of the Diaporthe disease complex that can include Phomopsis seed decay as well as pod and stem blight.

In other cases, cankers on stems were not due to disease, but hail. In areas that had drought stress in June, two-spotted spider mites were found and in early July, some areas that were wet, compacted or had high pH showed signs of IDC (iron chlorosis). In early September, SCN pressure was evident. Not only can SCN be a yield robber, but also can be a gateway for disease such as SDS. SCN can also be easily confused with nutrient deficiencies, and with soil testing I diagnosed not only SCN, but also phosphorus (P) and potassium (K) deficiencies.

This is the same variety planted side by side, but the variety on the right consists of PS SDS (ILeVO^®) in a plot near Avon, IL. This plot was planted April 14th, and SDS symptoms appeared early at the end of July.  The ILeVO^® treated plants yielded 22 bu/A more than the same variety on the left.

The soybean variety planted in a research plot near Hillview, IL on the right does not consist of the PI 188788 SCN resistance and SCN symptoms are clearly seen.

This field near Vandalia, Illinois, consisted of stunted and yellowing soybeans and was found to be deficient in P and K after a soil test was done.

Most soybean varieties have a genetic potential greater than 100 bu/A. However, a consistent variety, with the correct area of adaptation that includes the right agronomic traits, is needed for your particular production system and environment. So, of course, variety selection, planting date, drainage, soil type and agronomic decisions factor into soybean yield outcomes. Most importantly, Mother Nature factors into this yield equation and this is what we call G x E interaction or Yield = response of variety to growing conditions.

It was quite the season with seemingly good and frequent rains. Nevertheless, there were stresses out there that held back yield in many fields which kept them from going over 90 or 100 bushels.

Stephanie Porter is a Sales Agronomist with Burrus^® Hybrids with responsibilities that include educating growers and Burrus staff on all types of pests, weeds, diseases and other agronomic issues that affect corn, soybean and alfalfa production. Her territory encompasses Southern Wisconsin as well as Northern, Eastern and Southern Illinois.