Knowing the growth stage of your plants can be very important throughout the growing season. Plants have different requirements and stressors, depending on the stage it is in. However, we can’t just count on knowing when we planted it or how tall it is to know where it actually is developmentally. To make sure you best serve your plants’ needs (while also following label directions), we have put together a quick guide on how to growth stage your corn and soy plants.
How to Growth Stage a Corn Plant
Corn plants’ growth stages are driven by heat and are broken into two primary groups – vegetative and reproductive. The vegetative stages are labeled V1, V2, V3, etc., usually going up to V14 -V16. Each vegetative stage is marked by a fully collared leaf. If the leave isn't fully collared, it isn’t counted. Early season, when the plant is in its vegetative stage, the first thing to note is the “thumb” shaped leaf – this is the first leaf to emerge from the plant and is the only rounded leaf. The collar on this leaf marks V1. From there, each collared leaf gives you a progression of the growth stages.
Identifying growth stages later in the season can be a little tricky because the corn plant will often drop its initial leaves. Once this has happened, the plant has to be split open to identify what stage it is at. Each leaf emerges from a single growing point. When the plant is cut open, you will see a dark, upside down triangle. This mark counts for 4 vegetative stages as it is 4 compressed nodes. From there, you will count every node until you get to the remaining external collared leaf and continue counting from there. Since the early nodes don’t stretch out, typically the first 5-6 will actually be below the soil surface. The last vegetative stage is VT or when the plants tassel.
Reproductive stage begins when the plant has received around 1,400 growing degree days (GDDs), or close to that number depending on location and hybrid maturity. R1 is when you see your corn plant silking and after that point you use the kernels to help you determine its stage. At R2, you will notice the kernels blistering. Around the end of the third week of pollination, the corn plant should be at R3, also known as the “milk stage,” when the kernels will be full of a milky liquid. In R4, the sugar is more rapidly converted to starch and you’ll notice the kernels hardening. Around 40 days after pollination, the kernels will reach R5 or “dent,” signaled by the kernels denting in across the top. R6, the final reproductive stage, also known as “black layer,” signals physiological maturity. There is a noticeable black line and absence of the milky substance in the kernels.
How to Growth Stage a Soybean Plant
Soybean growth stages are mainly driven by photoperiod and are also broken into two groups: vegetative and reproductive. VE marks emergence. VC marks the first leaves which appear out of the cotyledons, which are the only unifoliate leaves the plant will produce. From there, knowing what growth stage you are at requires counting fully opened trifoliates. Each trifoliate, or group of three leaves, counts as one additional growth stage beginning with V1.
Summer solstice is the main trigger for producing flowers on soybeans, and the first flower signals reproductive growth stage R1. In indeterminate soybeans, the vegetation will continue to grow, which may lead to a rather long flowering period. Once blooms reach the top two nodes, the plant has reached R2 or full bloom.
R3 is when the podset begins, technically requiring a 3/16” long pod at one of the four top nodes. R4, or full pod, is reached when pod one’s top four nodes reach 3/4". The plant begins to seed at R5 when seed in the pod reaches 1/8" long, again on one of the four uppermost nodes. R6, or full seed, is when the pod on one of the upper four nodes is full of green seed.
Maturity is signaled by pod color as it transitions from green. Once one pod anywhere on the plant has changed to its mature color, it is R7 or beginning maturity. Once most (95%) of the plants have reached mature color, the plant is considered to be at R8 or full maturity.
Knowing the proper stage of your plants can have a big impact on in-season applications or proper testing times. Serious damage and loss can occur if timing is wrong. However, by using this guide, you can prevent issues by spending a little time in the field and discovering its growth stage.