By Jonathan Kleinjan
To say that the spring of 2019 has been a challenge for South Dakota producers is an understatement. According to the USDA-NASS, corn and soybean planting progress in SD was pegged at 19% and 4% on May 20th, respectively, which is far below the 5-year averages of 76% and 39%. Last week was the first time much of either crop was planted in SD.
Temperatures have since returned to below-normal levels and many producers may be concerned about the health of crops that were recently planted. Corn and soybeans are particularly susceptible to low-temperature stress during germination, emergence, and seedling stages. The inherent risks associated with low soil temperature environments include chilling injury and cold stress, delayed or uneven emergence, and greater seed exposure to soil-borne diseases and insects.
Chilling injury
Corn and soybeans are particularly sensitive to cold and wet soils during the imbibition period, which occurs as soon as the seed is exposed to moisture (usually immediately after planting). If the first water that enters into the seed to rehydrate cells (imbibition) is below 50° F, cells can rupture, which leads to non-viable swollen kernels or seeds and aborted growth of roots and shoots. The risk of injury largely occurs when planting into dry, cool soils immediately followed by a cold weather precipitation event. Corn seeded into wet soils with soil temperatures above the 50° F threshold for the first 48 hours after planting should germinate just fine. Soybeans have a shorter imbibition period and a soil temperature above 50° F for 24 hours is generally considered adequate for proper germination.
OTHER CONSIDERATIONS
Even if proper germination occurs, soil temperatures below the mid-40s for several days can be a cause for concern for emerging crops. Emergence may take 20 days or longer, depending on growing degree days (GDDs) accumulated after planting. It is possible to check the growing conditions for at any weather station in SD with the GDD tool at the SDSU Mesonet website. Remember that many soil-borne pathogens can substantially affect both corn and soybean emergence due to cold, wet soils, with root and seedling rots being a major factor. These conditions may compound plant health issues if factors such as soil crusting, ponding, compaction, or potential herbicide injury also exist.
HOW DO I TELL IF I HAVE INJURY TO MY CROPS?
Be patient. No one likes to hear “Let’s wait and see” but it is imperative to do so. With current cold temperatures, corn and soybean development can be significantly slowed from what many perceive as the “norm” this time of year, so patience in checking seedling development is vital.
When scouting for injury and stand establishment, be sure to check different parts of fields and remember that good yields are still possible even with reduced stands. There are several good extension publications available online discussing both corn and soybean stand evaluations.
Source: sdstate.edu