Authored by Lindsay Chamberlain (UW), Jim Specht (UNL) and Shawn P. Conley (UW)

August 1st is right around the corner and crop maturity timing concerns have erupted! These concerns are amplified in 2019 due to historically low GDU accumulations and late plantings that have significantly delayed overall soybean crop progress. Below we provide some estimates of specific crop developmental stages from both measured data in 2017 at our Arlington research station and estimated crop development using UNL SoyWater. Please use this information provided as estimates and not hard facts.

In 2017, we planted soybeans ranging from MG 0.2 to MG 7.5 in Arlington, WI on June 1 to see how these different MGs responded in WI. Fehr and Caviness soybean growth stages were noted twice per week, including the “Beginning” and “End” of each grain-fill (R3-R6) growth stage. The “beginning” was noted when the size pod was present anywhere on the plant, and the “end” was when no more pods of that stage were present. The Fehr and Caviness growth stage system refers to the top 4 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 the figure by the colored lines, and the entire width of the colored lines depict the grain fill period (Figure 1). Using 30 year climatology data (Figure 2.), albeit a bit out dated, there is a 50% risk that a 3.0 or later soybean planted on June 1 will experience 32 degree temperature during the R7 growth stage. This one year of observation is also confirmed using the SoyWater model (Table 1). Additional planting date by maturity group combinations that are at risk (50%) of freeze damage in the R7 growth stage in southern WI are highlighted below in Table 1. Those cells that contain a (-) 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 (50%) of freeze damage in the R7 growth stage in northern WI are highlighted below in Table 2. Those cells that contain a (-) are not likely to reach maturity.

We feel that these values are robust and provide growers with a reasonable risk assessment for the given planting date by maturity group interactions. Regardless lets all hope for a late and dry fall!

Image 1. Phenological development of several maturity group soybeans (0.2 to 7.5) grown at Arlington WI in 2017.

Table 1. Estimated Soybean Developmental Stages for Arlington WI using SoySim Based on Soybean Planting Date and Maturity Group.

Planting Date MG R1 R3 R5 R7
15-May-19 1 7-Jul 20-Jul 7-Aug 29-Aug
15-May-19 1.5 11-Jul 24-Jul 12-Aug 7-Sep
15-May-19 2 13-Jul 29-Jul 16-Aug 14-Sep
15-May-19 2.5 14-Jul 31-Jul 19-Aug 19-Sep
15-May-19 3 15-Jul 2-Aug 22-Aug 24-Sep
1-Jun-19 1 15-Jul 29-Jul 14-Aug 3-Sep
1-Jun-19 1.5 17-Jul 31-Jul 17-Aug 11-Sep
1-Jun-19 2 21-Jul 5-Aug 22-Aug 20-Sep
1-Jun-19 2.5 23-Jul 7-Aug 25-Aug 26-Sep
1-Jun-19 3 24-Jul 10-Aug 29-Aug 1-Oct
15-Jun-19 1 22-Jul 4-Aug 19-Aug 8-Sep
15-Jun-19 1.5 25-Jul 7-Aug 23-Aug 17-Sep
15-Jun-19 2 29-Jul 10-Aug 26-Aug 25-Sep
15-Jun-19 2.5 31-Jul 13-Aug 30-Aug 1-Oct
15-Jun-19 3 2-Aug 16-Aug 3-Sep 8-Oct
30-Jun-19 1 9-Aug 19-Aug 1-Sep 21-Sep
30-Jun-19 1.5 14-Aug 24-Aug 6-Sep 4-Oct
30-Jun-19 2 17-Aug 27-Aug 12-Sep 16-Oct
30-Jun-19 2.5 20-Aug 30-Aug 18-Sep 29-Oct
30-Jun-19 3 22-Aug 2-Sep 24-Sep 21-Nov
15-Jul-19 1 26-Aug 3-Sep 19-Sep 10-Oct
15-Jul-19 1.5 30-Aug 8-Sep 26-Sep 29-Oct
15-Jul-19 2
15-Jul-19 2.5
15-Jul-19 3

Cells with a (-) indicate that SoyWater did not compute Rn stages for that planting date and maturity group because the growing season is too short to reach physiological maturity.

Table 2. Estimated Soybean Developmental Stages for Chippewa Falls WI using SoySim Based on Soybean Planting Date and Maturity Group.

Planting Date MG R1 R3 R5 R7
15-May-19 1 2-Jul 16-Jul 3-Aug 26-Aug
15-May-19 1.5 6-Jul 20-Jul 8-Aug 5-Sep
15-May-19 2 9-Jul 24-Jul 12-Aug 12-Sep
15-May-19 2.5 11-Jul 27-Jul 15-Aug 18-Sep
15-May-19 3 12-Jul 29-Jul 19-Aug 22-Sep
1-Jun-19 1 10-Jul 23-Jul 9-Aug 31-Aug
1-Jun-19 1.5 12-Jul 26-Jul 12-Aug 8-Sep
1-Jun-19 2 14-Jul 29-Jul 15-Aug 15-Sep
1-Jun-19 2.5 15-Jul 31-Jul 18-Aug 20-Sep
1-Jun-19 3 16-Jul 2-Aug 22-Aug 25-Sep
15-Jun-19 1 21-Jul 2-Aug 17-Aug 7-Sep
15-Jun-19 1.5 24-Jul 5-Aug 21-Aug 16-Sep
15-Jun-19 2 26-Jul 8-Aug 24-Aug 24-Sep
15-Jun-19 2.5 30-Jul 12-Aug 29-Aug 3-Oct
15-Jun-19 3 30-Jul 13-Aug 1-Sep 8-Oct
30-Jun-19 1 7-Aug 16-Aug 31-Aug 20-Sep
30-Jun-19 1.5 10-Aug 20-Aug 4-Sep 2-Oct
30-Jun-19 2 13-Aug 24-Aug 9-Sep 15-Oct
30-Jun-19 2.5
30-Jun-19 3
15-Jul-19 1 21-Aug 30-Aug 14-Sep 6-Oct
15-Jul-19 1.5
15-Jul-19 2
15-Jul-19 2.5
15-Jul-19 3

Cells with a (-) indicate that SoyWater did not compute Rn stages for that planting date and maturity group because the growing season is too short to reach physiological maturity.

Image 2. Median date of 50th percentile of first 32 degree frost in WI.

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