Tune into soybean growth stages
During the growing season, we hear a lot about silking, blister and dent. There isn’t much chatter about beginning flower, full flower, beginning pod and full pod, though. Despite the large soybean acreage in our region, soybean growth stages just aren’t discussed like corn growth stages. Maybe it is because soybean stages aren’t as recognizable or as noticeable as tasseling and cob development. Regardless, I believe every farmer should pay attention to soybean stages so he can implement practices to boost development in each stage and preserve yield potential.
The soybeans in our region spend at least half of their time in the reproductive stage. Our indeterminate beans continue on with the vegetative stage after they begin reproduction. Soybeans can sense when the nights become longer and, depending on their growth stage, begin to flower in the following days. Northern soybeans typically start flowering around July 1, depending on planting date. Soybeans are amazing. Those planted farther north than their adapted range will delay flowering; those planted farther south than their adapted range will shorten their vegetative growth period and allow for earlier flowering and earlier maturity.
The flowering stages of soybean reproduction are beginning flowering (R1) and full flower (R2). R1 occurs when one flower is located on the main stem. Flowering begins at the third to sixth node. R2 is reached when a flower is present at one of the two uppermost nodes of the main stem. Plants normally have eight to 12 trifoliates. The plant is rapidly expanding its root system and increases its uptake of nitrogen, phosphorus and potassium.
Applying a fungicide for white mold prevention is recommended during R2 in areas with white mold prevalence.
Pod development follows with beginning pod (R3) and full pod (R4). At R3, one of the four uppermost nodes has a pod that is 3/16 of an inch in length. Stress can limit the number of pods produced, as well as each pod’s beans. R4 is reached when one of the four uppermost nodes has a pod that is 3/4 of an inch in length. This is a stage of rapid pod growth on the plant. Many postemerge chemicals are now off-label during pod development. Check labels for growth stage recommendations.
Seed development follows with beginning seed (R5) and full seed (R6). When a seed measures 1/8 of an inch in a pod on one of the four uppermost nodes, the plant is in R5. This typically occurs about a month before full maturity. The plant is near its maximum height and node number. Nitrogen fixation has peaked, and dry matter is being distributed to the seeds. R5 is the last stage where an insecticide application for soybean aphid control is recommended. R6 is reached when a pod contains a green seed that fully fills the pod cavity. Root growth is complete at this stage, and the maximum pod weight has been reached.
• It’s important to recognize soybean growth stages.
• Steps to protect yield are linked to growth stages.
• Fungicide application is recommended at R2 stage.
The final stage is plant maturity, with beginning maturity (R7) and full maturity (R8). R7 is recognized by one pod anywhere on the plant that is mature in color. The leaves are turning yellow, and the plant will be fully mature in seven to 15 days, when 95% of pods have reached a mature color (brown or tan).
Spelhaug is an agronomist with Peterson Farms Seed, Harwood, N.D. Follow him on Twitter at @PFSAdam, and read his contributions to The Peterson Blog at . For more information, contact him at 866-481-7333 or .
This article published in the August, 2014 edition of DAKOTA FARMER.
All rights reserved. Copyright Farm Progress Cos. 2014.