Section 2 - Crop Development

Vegetative Stages

Soybean Growth Stages

Soybean plant development is divided into vegetative (V) and reproductive (R) stages. With the exception of the first two stages, the (V) stages are designated numerically as V1, V2, V3, etc. through V(n), where (n) represents the number for the last node stage of a specific variety. The (n) will fluctuate with variety and environmental differences. The eight R stages are simply designated numerically.

The V stages following VC are numbered according to the uppermost fully developed leaf node. Start with the unifoliolate leaf node when counting the number of fully developed leaf nodes. A leaf node is fully developed when the leaf above it has leaflets which are fully unrolled. That is, the leaflet edges are no longer touching.

Vegetative Stages

Stage Description

VE -- Emergence

VC -- Cotyledon

V1 -- Unifoliolate and first trifoliolate leaves are fully developed

V2 -- Unifoliolate and first two trifoliolate leaves are fully developed

V3 -- Unifoliolate and first three trifoliolate leaves are fully developed

V(n) -- Unifoliolate and (n) trifoliolate leaves are fully developed

Reproductive Stages

Stage Description

R1 -- Open flower at any node on the main stem

R2 --  Open flower at one of the two uppermost nodes on the main stem with a fully developed leaf

R3 -- Pod is 3/16 inch long at one of the four upper- most nodes on the main stem with a fully developed leaf

R4 -- Pod is 3/4 inch long at one of the four upper- most nodes on the main stem with a fully developed leaf

R5 -- Seed is 1/8 inch long in the pod at one of the four uppermost nodes on the main stem with a fully developed leaf

R6 -- Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf

R7 -- One normal pod on the main stem that has reached its mature pod color

R8 --95% of the pods have reached their mature pod color

Sources: Iowa State University, Purdue

Soybean Growth Stages Online

• http://weedsoft.unl.edu/documents/GrowthStagesModule/Soybean/Soy.htm

• www.planthealth.info/pdf_docs/soy_growthstages_msu.pdf

• http://extension.agron.iastate.edu/soybean/production_growthstages.html

• www.ag.ndsu.edu/pubs/plantsci/rowcrops/a1174/a1174w.htm

Bloom Key Soybean Development Stage

The beginning bloom stage or R1 stage in soybeans is marked by the plants having at least one flower on any node of the main stem. If there is still a need to spray for weeds, check the label carefully for spraying after flowering begins. There are a number of herbicides that can be used after flowering begins. Always read and follow label guidelines when using pesticides.

Soybeans are at 50% bloom when an open flower can be found on every other plant in a row. Flowering, unlike maturity on soybeans, begins toward the bottom of the plant (at the third to sixth node) and then progresses upward and back downward. Branches off of the main stem will flower a few days later than the main stem. While flowering begins at the base of the plant and proceeds to the top of the plant, physiological maturity of the beans will progress anywhere on the plant stem.

Normally, soybean pods will be mature in the middle or top of the plant and down. Thus, remember to check pods toward the bottom of the plant when determining if harvest time has come.

Flowering of soybeans is an important time in bean growth and development. At stage R2, full bloom, each plant has accumulated about 25% of its total dry weight and nutrients; it has attained about 50% of its mature height; and, it has produced 50% of its total mature node number.

This later flowering stage begins the period of very rapid N-P-K and dry matter accumulation that will continue through R6. Also, during flowering, the soybean plant gears up on its nitrogen fixation in order to provide for the demands of the plant. Scout for disease and insect problems (aphids) during this critical early time period of flowering.

Corn Growth Stages

Corn plant development can be divided into vegetative (V) and reproductive (R) stages. The (V) stages are designated numerically as V1, V2, V3, etc. through V(n) where (n) represents the number of leaves with visible collars. The first and last (V) stages are designated as VE (emergence) and VT (tasseling). The six reproductive stages are simply designated numerically.

Each leaf stage is defined according to the uppermost leaf whose leaf collar is visible. Loss of the lower leaves will begin about V6 due to increased stalk size and nodal root growth. To determine the proper leaf stage after lower leaf loss, split the stalk lengthwise and inspect for internode elongation. The first node above the first elongated internode is generally the fifth leaf node. This fifth leaf node can be used as a reference point for counting the top leaf collar.

Vegetative Stages

Stage Description

VE -- Emergence

V1 -- One leaf with collar visible

V2 -- Two leaves with collars visible

V(n) -- (n) leaves with collars visible

VT -- Last branch of tassel is completely visible

Reproductive Stages

Stage Description

R1 -- Silking - silks visible outside the husks

R2 -- Blister - kernels are white and resemble a blister in shape

R3 -- Milk - kernels are yellow on the outside with a milky inner fluid

R4 -- Dough - milky inner fluid thickens to a pasty consistency

R5 -- Dent - nearly all kernels are denting

R6 -- Physiological maturity - the black abscission layer has formed

Sources: Iowa State University, Purdue

Next Page