Marestail (Conyza canadensis) is one of the most difficult weeds to manage in no-till soybean. While classified as a winter annual, the plant has significant emergence in both late summer/early fall and in the spring. This extended emergence period greatly complicates management since the success of postemergence products is closely tied to plant size. Attempting to control populations at the time of planting often results in control failures as fall-emerged plants are too large for acceptable control.
Soybean farmers have kept the soybean cyst nematode (SCN) “in check” for decades simply by growing SCN-resistant soybean varieties. Unfortunately, prolonged use of varieties with SCN resistance genes from a breeding line called PI 88788 has resulted in SCN populations building up increased reproduction on resistant varieties. Almost all (97%) soybean varieties available to grow in Iowa have SCN resistance genes from PI 88788. This situation has led to dramatic and often unnoticed increases in SCN numbers in fields.
Need to know specifics
Now more than ever, farmers need to know if their fields are infested with SCN and what the numbers are. The higher the number of SCN eggs in the soil, the greater the yield loss - even with resistant soybean varieties.
When looking for soybean varieties, it is important to give as much thought to the process as you give to choosing corn hybrids. If you only choose one or two soybean varieties and do not take into consideration management and environmental factors of your operation, you are likely limiting yield potential.
The soybean cyst nematode (SCN) continues to be the most-damaging soybean pathogen in the US and Canada. The nematode is widespread in fields through Iowa and much of the Midwest. Management options for SCN include growing nonhost crops (such as corn), growing SCN-resistant soybean varieties, and using nematode-protectant seed treatments. Resistant soybean varieties have allowed farmers to produce profitable soybean yields in SCN-infested fields and keep SCN population densities relatively in check.
When you think about which hybrids to plant next season, make sure to take into account all the relevant factors. When selecting hybrids, prioritize yield potential and risk management. There are a number of other components to consider as well, including transgenic options, disease tolerance, maturity, grain dry down, standability, stalk quality, and early season vigor ratings.
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.