Will My Late Planted Soybeans Mature Before a Killing Frost?

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!

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.

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