Crop-maturity timing concerns have erupted. Those concerns are amplified in 2019 due to historically reduced growing-degree-unit accumulations. Late plantings have significantly delayed overall soybean-crop progress. We provide some estimates of specific crop-developmental stages from both measured data in 2017 at the University of Wisconsin-Arlington Agricultural Research Station, and estimated crop development using the University of Nebraska-Lincoln’s SoyWater tool. Use the information provided as estimates and not hard facts.

We planted soybeans June 1, 2017, ranging from MG 0.2 to MG 7.5 at the Arlington research station, to learn how those different MGs responded in Wisconsin. Fehr and Caviness soybean-growth stages were noted twice per week, including the “beginning” and “end” of each grain-fill growth stage – R3 to R6. The beginning was noted when the size pod was present anywhere on the plant. The end was when no more pods of that stage were present. The Fehr and Caviness growth-stage system refers to the top-four nodes only, so pods of many stages can be on the plant at the same time. The beginning and end of each growth stage is noted on Figure 1 by the colored lines. The entire width of the colored lines depict the grain-fill period.

Using 30-year climatology data in Figure 2 – albeit a bit outdated – there is a 50 percent risk that 3.0 or later soybeans planted June 1 will experience 32-degree temperature during the R7 growth stage. That one year of observation is also confirmed using the SoyWater model. Additional planting dates by maturity-group combinations that are at risk of freeze damage in the R7 growth stage in southern Wisconsin are highlighted in Table 1. Those cells that contain a hyphen are not likely to reach maturity.

A similar analysis was conducted using SoyWater for our Chippewa Falls location. Planting date by maturity-group combinations that are at risk of freeze damage in the R7 growth stage in northern Wisconsin are highlighted in Table 2. Those cells that contain a hyphen are not likely to reach maturity.

We believe the values are robust and provide growers with a reasonable risk assessment for the given planting date by maturity-group interactions. Regardless let’s all hope for a late and dry fall.

Visit coolbean.info and hprcc-agron0.unl.edu/soywater for more information.

Lindsay Chamberlain is a graduate research assistant at the University of Wisconsin-Madison. Jim Specht is a professor emeritus of agronomy at the University of Nebraska-Lincoln; visit agronomy.unl.edu/specht for more information. Shawn Conley is an associate professor of agronomy at UW-Madison; he is a UW-Division of Extension soybean and wheat specialist.