Extension

Corn and soybean yields in 2017 were better than expected, which will add to the largest grain surpluses in recent years. As of the November 9, 2017 USDA crop production estimates, national corn yield estimates exceeded 2016 production and were closer to 2016 production in Iowa than preharvest expectations. Soybean yields are estimated to be lower than in the record year of 2016, but total US supply will be larger due to acreage increases.

Soybean are nearing maturity across Iowa with minimal delay due to cool temperatures compared to 2016. However, soybean sensitivity to day length speeds up crop development towards physiological maturity. During senescence carbohydrates are converted into oils. Soybean seed moisture changes very little, remaining near 60 percent during the de-greening period. As the pods turn to mature color at the beginning of maturity stage (R7), seed dry matter accumulation is complete and seed moisture rapidly decreases.

Lately there have been lots of questions asked about sampling fields for plant-parasitic nematodes that feed on corn. This diverse group of microscopic worms includes some species that cause yield loss at very low population densities (numbers), other species that are not harmful until population densities reach many hundreds or more per 100 cm3 (a little less than a half-cup) of soil, and still other species that are not thought to be harmful to corn at all.

It is common for Iowa fields to have several species of plant-parasitic nematodes present at low numbers. It’s only when numbers reach damaging levels that symptoms of injury will appear.

Corn harvest is fast approaching. This year’s corn maturity is about 5-10 days behind normal. With field dry down occurring in late September and October this year, there is the potential for a later harvest of corn at a higher moisture content. The rule of thumb has been that corn dries at a rate of 0.5 to 1.0% per day in September, 0.25 to 0.5% per day in October, and almost no drying occurring in November. Of course, these rules of thumb can change with favorable or unfavorable weather conditions.

Water loss from corn kernels is divided into two phases. The first phase is kernel moisture loss before maturity in which water loss is related to accumulation of dry matter in kernels. After black layer, moisture loss occurs through evaporation of water from the kernel surface.

The EPA recently announced changes to the new dicamba labels in response to widespread off-target plant injury in 2017.  The most significant change is classification of the new dicamba formulations as Restricted Use Products. Other changes will reduce the hours available to spray soybean, including 1) restricting applications to between sunrise and sunset, and 2) reducing the maximum wind speed during application from 15 mph to 10 mph. The ability to cover all acres in a timely manner has always been an issue and these new limits will add to that difficulty.

Micronutrients are needed in very small quantities by plants, but are essential for their growth and production. A search for understanding how micronutrients can be better managed in the Midwest’s soybean fielsoybean fieldds has led to new research and a regional publication on the topic.

This research and general management guidelines are summarized in the publication “Micronutrients for Soybean Production in the North Central Region” (CROP 3135) and is available through the Iowa State University Extension Store. Antonio Mallarino, professor and extension specialist in agronomy at Iowa State University, led a team of researchers and fertility extension specialists from five universities across the Midwest who worked on the project.

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