Planting is underway in many areas of the country. Most regions are focused on corn, but a few are turning to soybeans. Planting soybeans in the Midsouth region is fairly common this time of year, but for those considering starting soybeans this early in the Midwest, don’t forget to consult your extended weather forecast and check the current state of your soil. Planting soybeans into cool, wet soil can lead to emergence problems and can leave them more vulnerable to insect and disease pressure in the longer term.
Germination Issues
Soybeans have a few different stages of the germination process; the imbibitional phase, which takes place 24–48 hours after planting, and the osmotic phase. During these phases, the soybean seed experiences a fast uptake of water (imbibitional) and then a slow uptake of water (osmotic). If you plant seed into wet, cool soil and then factor in water uptake and a cooler-than-average forecast, it is now at risk of chilling injury. If soil temperatures dip below 50 degrees Fahrenheit 48 hours after planting, the seed coat could be compromised, leading to inconsistent hydration of the seed. According to the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln, “Chilling during the first phase can cause severe problems because the imbibed water is needed to rehydrate the cotyledons and embryo to the point that cell membranes become functional. Cold temperatures interfere with proper hydration of those membranes.”
Temperature inversion is also something that may cause germination issues. According to the Environmental Protection Agency, temperature inversion is an atmospheric condition that occurs when a layer of warm air traps a layer of cold air close to the ground. Plants grow toward heat and are not influenced out of the ground by gravity. When seed experiences warmer temperatures below ground than above ground, the plant germinates in a down and up or corkscrew pattern. This situation is likely to cause emergence and stand count issues later on.
Post-Emergence Concerns
In soybeans, the growing point is above ground, which is different than a corn plant. While soybean plant tissue can typically tolerate freezing temps, a cold snap after soybeans are up can freeze off a field planted too early if temps drop below 30 degrees for several hours. However, this can vary based on ground cover, landscape of a field, canopy density and row spacing.
Increased Disease Pressure
Germination issues caused by cold, wet soils can slow root development of a plant and leave it more susceptible to disease pathogens. Diseases such as Phytophthora, Rhizoctonia and Pythium root rot may be more prevalent in early planted soybeans. Iowa State University Extension and Outreach notes, “If there is a history of seedling diseases from Phytophthora, Pythium, Rhizoctonia, or Fusarium, fungicide seed treatment is recommended.” Soybean sudden death syndrome can also present itself in early planted soybean fields because of the plant’s slowed germination process.
Increased Insect Pressure
If you have a history of bean leaf beetles in your fields, know that they still may be present and have overwintered in your soil. If you’re planting soybeans early in that same field, chances are the beetles will reemerge and begin feeding on the soybeans as they emerge. That said, Ohio State University Extension notes that unless beetle densities are abnormally high and their feeding significant, there should not be a large risk of economic damage caused by the early season leaf defoliation they cause. This can be managed with a foliar insecticide. If you haven’t planted yet, you can also consider a seed treatment with insecticide.
Right now it’s important for growers to have patience. Don’t mud your seed in by planting into wet ground. And remember, crops planted before the earliest recommended planting date may not be eligible for replanting payments through crop insurance should something go awry with your field. Be sure to consult with your crop insurance agent to get those dates before you hit the field.