Timing Your Soybean Fungicide Application Amid Heavy Rainfall

When heavy rainfall occurs, it's common for soybean growers to contemplate a fungicide application. The best time for such an application usually falls between the R2 and R4 growth stages, with the R3 stage being the prime window.

What's R2, you might ask? It's also known as the 'full flower' stage and is recognized when an open flower appears within one of the top two nodes with fully expanded trifoliate leaves. A fully expanded trifoliate means that the three individual leaflets have grown so that they no longer touch. These leaves grow apart to the point where they no longer touch each other.

The yellow circle in the image below encompasses the two uppermost nodes.

If a flower is located on at least one of those nodes, the plant has achieved 'full flower'. So, when facing heavy rainfall, remember these stages to optimally time your fungicide application.

Photo by BASF Staff

Most full-season soybeans, and many double precision-crop soybeans, are at or beyond the R2 growth stage. The next stage in soybean reproductive growth is R3. R3 is when a pod, approximately 3/16" in length, is located in the top four nodes of the plant. The yellow circle identifies the top four nodes in the graphic below. Because a pod that measures at least 3/16" can be found at one or more of those nodes, this soybean in is R3, or the 'beginning pod' growth stage.

Photo by BASF Staff

Many soybeans may still be in 'beginning pod'; however, some shorter-season varieties and earlier planted fields may have progressed to R4, or 'full pod'. During 'full pod', a pod 3/4" in length can be found in at least one of the top four nodes of the plant. The yellow circle denotes the top four nodes on the plant in the graphic below. Because a pod 3/4" in length exists at one or more of these nodes, this plant has achieved 'full pod'.

Photo by BASF Staff

Scout your fields! If soybeans are in any of these three growth stages, it is a good time to apply a fungicide. While staging your beans, be on the lookout for insect pests such as the bean leaf beetle, stinkbugs, and grasshoppers. Remember, the threshold for defoliation of reproductive stage soybeans is 20%. Some of these pests may also feed on pods, which can damage the seed and leave entry points for disease pathogens.

Applying Priaxor® Fungicide + Fastac® Insecticide is a good way to protect your soybeans from fungal pathogens and insect pests.

Always read and follow label directions.

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