Identifying Late Season Soybean Growth Stages

Proper identification of late season soybean growth stages will assist with decisions to be made regarding late season management termination (i.e. insecticide termination, irrigation termination) as well as preparation for harvest aid applications (see: https://www.mississippi-crops.com/2016/08/19/soybean-harvest-aids-3/). Keep in mind that indeterminate varieties begin maturing at the bottom of the plant and will progress upwards while determinate varieties will mature uniformly up and down the plant. Observations for determining the growth stage should be taken from pods in the upper four nodes of indeterminate varieties and anywhere on the plant for determinate varieties.

The following points will help in identifying the late reproductive growth stages in soybean:

• R6 – seed completely filling the pod cavity
• R6.5 – seed separated from the protective membrane within the pod

Remember, the R6 growth stage is only achieved once the seed have completely filled the space within the pod. At this stage, seeds will often be “squared off” as they push together within the pod. The R6.5 growth stage typically occurs 7-10 days following R6, depending on planting date and environmental conditions. When the plant reaches R6.5, the seed should easily separate from the protective membrane within the pod. At this time, the plants are still green and the pod will begin to yellow. The following image may help in identifying these two important growth stages: