Ag Bites — Soybean Staging — August 2, 2012

In this week’s edition of Ag Bites, Adam discusses staging of soybeans undergoing reproduction, showing plants ranging from R2 to R5. He also makes recommendations for spraying fungicides dependent on stage.

Counting down from the first fully expanded trifoliate to the fourth node is the most reliable way to stage a reproducing soybean plant. If there is a flower on the fourth node, the plant is in full flower or R2. R2 is the correct time to apply a fungicide if looking for white mold control.

In R3, pods are beginning to form and are about 1/4″ in length. R3 is the time many fungicide applications are happening for plant health and to control Brown Spot or other diseases like Frog Eye. If stress occurs during the R3 stage, pods may be aborted.

In the R4 stage, pods are at least 3/4″ long. Aborting beans is the largest threat during R4.

If a bean can be felt in the pod, the plant is in the R5 stage. R5 is a long stage where most dry matter is gained and soybeans are filled. Stress during R5 can cause reductions in weight. See full video transcription below.

“Welcome to this week’s edition of Ag bites for Peterson Farms Seed. Today we’re going to talk about staging soybeans during the reproductive stages. We have some late planted soybeans that we can take a look at, some of the early stages, along with our replicated plot, and our April fourth soybeans that are really far along, so we have a wide range of a maturities out here.

A lot of different stresses can affect different parts of the plant at these stages. This plant that I pulled from these late planted beans, that were planted at the end of June, is an R2 stage full flower. The easiest way for staging soybeans, is you count the top four nodes. You count down from the first fully expanded trifoliate, but if the trifoliate leaves are touching you don’t count that.

You start from the center of the axle where the first fully expanded trifoliate is, and countdown four nodes. If you have flowers in any of those top four nodes, you have full flower. R1 beginning flower, started right after the solstice at the end of June. Right now, we’re in R2, and this is the time you want to be putting on a fungicide if you’re trying to go after white mold control, which it is still not the greatest, at controlling white mold, but that’s going to be the earliest.

The next stage is getting R3. At that time, at that fourth node, you’re looking at the pod that is about a quarter of an inch and then you’re in R3.And this is the staging time that a lot of guys are putting fungicides on their soybeans for plant health or maybe trying to get ahead of brown spot or some of the other diseases like frogeye, but that is one that we don’t get into because it is more prevalent in the south.

So that’s where we want to be on the plant, that little quarter inch pod is getting you into the R3 or R4 stage. This pod is at least three quarters of an inch, so this one is getting close to R5, but that pod is about three quarters of an inch long. What we could be losing at R4 is it still could suck back some of the beans. At R3, we could be losing some pods, but R4 we could be aborting some of the beans.

Getting into R5, on the fourth node or above, if you can actually feel a soybean in there or you can feel the bump of any bean, you are near or in R5. Because R5 is quite a long stage, this is where we’re gaining most of our dry matter and filling most of our soybeans. This is also when any stressors can happen in R5, and then R6 is when those beans are actually touched together in the pod in full seed. That’s when we start losing weight in our soybeans and affecting yield that way.

That’s why it’s good to know the stages on your soybeans, especially if you’re out scouting for aphids, or spider mites and figuring out when you should be applying. Our recommendation is still applying through R6 and putting water if you’re irrigating through R6. That plant is still putting a lot of its dry matter in that seed, and building your yield so, you want to be protecting it, especially this year with our drier weather.”