Soybeans are soybeans. You may think you know all you need to know about growing them. If you don’t know how to stage soybean growth so you can talk with your consultant or retail dealer and understand terms such as “V4” or “R3,” then you may be missing out on information that could help you make better decisions.
Steve Gauck carries a copy of the Purdue University Corn & Soybean Field Guide in his pocket as he scouts the Soybean Watch ’18 field. He finds it useful for identifying insects and disease symptoms he sees in the field, but he says it’s also helpful in telling stage of crop growth. Gauck is a Beck’s sales agronomist based near Greensburg, Ind. Beck’s is the sponsor of the Soybean Watch ’18 project, which follows a soybean field throughout the entire growing season with the goal of highlighting situations others might find in their fields.
Here is a brief rundown of key soybean stages. Refer to the Purdue field guide for more details.
• VE. The cotyledons and growing point are above the soil. The cotyledons are the two halves of the soybean seed that emerge from belowground.
• VC. The cotyledons are expanded, and the first set of unifoliate leaves are also fully developed.
• V2, or second node. The V stages progress based on the number of leaflets and trifoliate leaves showing on the plant. V stands for “vegetative.” At V2, margins of the leaflets of the second set of trifoliate leaves no longer touch each other.
• V6. Margins of leaflets of the sixth set of trifoliate leaves no longer touch. The plant is about ready to switch from the vegetative stage to the reproductive stage.
• R1, or beginning bloom. There is a flower open at any node on the main stem. Gauck notes that while flowering is primarily controlled by daylength, planting date can also play a role in when a variety begins to flower in any given year.
• R2, or full bloom. You will find an open flower at one of the two uppermost nodes of the main stem. The leaf is unrolled or flat.
• R3, or beginning pod. You find a pod at least one-quarter-inch long at one of the four uppermost nodes on the main stem with a completely unrolled or flat leaf. This is often the recommended time to make fungicide applications in soybeans, Gauck says.
• R4, or full pod. A pod on one of the four uppermost nodes of the main stem is at least three-quarters of an inch long. Gauck points out that percentage of leaf loss is more critical at these reproductive stages than earlier in the season. In other words, a plant may be able to tolerate 30% leaf loss without affecting yield in vegetative stages, but perhaps only 15% to 20% before yield is affected if insects are feeding during these key reproductive stages.
• R5, or beginning seed formation. Seed is at least one-eighth-inch long in one of the four uppermost nodes on the main stem.
• R6, or full seed. Seeds fill the pod cavity on one of the four uppermost nodes of the main stem.
• R7, or beginning maturity. More than one pod on the main stem is beginning to yellow and show its mature color.
• R8, or full maturity. Ninety-five percent of the pods on the plant have obtained mature color.