Identifying Late Season Soybean Growth Stages
DR. TRENT IRBY
MISSISSIPPI STATE, MISS.
As we move closer to maturity, there are many decisions to be made on termination timing of various management practices. At this time of the season, we can use late season soybean growth stages as a guide to decide when to terminate these practices. Other than redbanded stink bug management, the general goal is to reach the R6.5 growth stage so that we can terminate other insect and foliar disease management practices as well as soybean irrigation. At this point, it’s time to consider soybean desiccation and manage redbanded stink bugs where necessary while preparing for harvest.
Proper identification of late season soybean growth stages is key to making these termination decisions. One thing to keep in mind is the location on the plant where you evaluate the current growth stage. On determinate varieties, the growth stage can be identified at any place on the plant. On indeterminate varieties, growth stages need to be identified in the upper four nodes of the plant. The reason being that indeterminate varieties begin maturing at the bottom of the plant and will progress upwards as the plant grows, while determinate varieties will mature uniformly up and down the plant. Keep in mind that in Mississippi, the majority of varieties we grow are indeterminate in growth habit.
The following descriptions will help in identifying the various late season growth stages in soybean:
• R5 – beginning of seed development
• R6 – seed completely fill the pod cavity
• R6.5 – seed separated from the protective membrane within the pod
• R7 – one pod mature in color located anywhere on the plant
• R8 – 95 percent of pods are mature in color
Remember, the R6 growth stage is achieved once the seed have completely filled the space within the pod. The easiest way to identify this is to open a pod and look for seeds that have “squared off” as they have pushed together within the pod. The R6.5 growth stage typically occurs 7-10 days following R6, depending on planting date, relative maturity, environmental conditions, etc. When the plant reaches R6.5, the seed should easily separate from the protective membrane within the pod. Soybean leaves when the plant reaches R6.5 will still be green in color but the pods will begin to yellow at this time. ∆
DR. TRENT IRBY: Extension Soybean Specialist, Mississippi State, Miss.
