Part 1, Section 6: Soybean
Soybean
Determination of Soybean Growth Stage
Knowledge of soybean growth stages is important to time pest scouting, apply certain pesticide sprays such as insecticides to control soybean aphid and foliar fungicide to control diseases, and document growth stage at the time of an injury event such as hail for insurance purposes.
Soybean growth stages are based on the vegetative (leaves and nodes) and reproductive (flowers, pods, and seeds) development of the plant and are designated with the letters V and R. The V (vegetative) stages refer to the number of nodes with a fully expanded leaf. A leaf is considered fully expanded when the leaflets of the next node have unrolled far enough so that their edges are not touching. The vegetative stage is determined by counting the number of nodes - starting at the unifoliate leaf - that have fully expanded leaves. For example, plants in the unifoliate stage are designated V1, plants with five nodes with completely unrolled leaves are in stage V5, and plants with twelve nodes with completely unrolled leaves are in stage V12.
For R (reproductive) stages, with the exception of stages R1 and R2, examine the reproductive structures on the upper four nodes that have fully unrolld leaves. Stage R1 indicates a flower present at any node. Stage R2 indicates a flower immediately below the node with the uppermost unrolled leaf. The stages progress through pod and seed development to yellowing and physiological maturity (Table 1.6-5).