Every discipline has its go-to standard of reference. In parliamentary procedure, the standard is “Robert’s Rules of Order.” If someone questions how an ag group functions or how a meeting should operate, that is the book where everyone looks for answers. In agronomy, specifically in growth staging for soybeans, the standard is an Iowa State University Extension publication. Complete with pictures, it’s been the go-to source for decades.

“The history behind how ISU became an authority on soybean growth staging goes back at least to the early 1970s, and probably longer,” says Mark Licht, Extension cropping systems specialist in corn and soybean management at ISU. “We had several professors who felt it was important and worked diligently to put together resources back during that period.”

Why was it such a big deal? “The fundamental reason was that as soybean researchers, they needed a way to communicate with one another,” Licht explains. “If someone at ISU was working on the same soybean project as someone in Minnesota or Wisconsin, they needed to be able to talk the same language. When someone said they were working with V3 stage soybeans, it was important for researchers everywhere to instantly identify what that meant. It was important to have a standard for stages of development.”

Order Soybean Growth and Development (PM 1945) online, or view some of the information, including pictures, here.

More informed decisions

Today, growers benefit from learning the growth stages of soybeans and being able to determine those stages easily in their own fields, Licht says. “It makes management decisions easier if everyone talks the same language when it comes to growth stages,” he adds.

Here are key examples:

Herbicide use. Most herbicide labels don’t talk about just height of soybeans. “They refer to growth stages, often in terms of informing you when it’s OK or not OK to apply the product,” Licht says. “Staging the crop in advance is key to making sure you follow labels that talk about growth stages.”

Hail damage assessment. Hail can be more damaging at some stages than others. And when you’re determining if plants will likely recover, plus estimating potential yield impact, it’s important to know the stage of soybean growth, Licht says.

Fungicide application. If you apply fungicides routinely, many product labels recommend applying at the R3 stage, but some want an R2 application. Knowing how to tell the difference is key. “Later in the season, if diseases appear, it’s important to know where you are in seed fill and development to know if a fungicide application might still pay,” Licht says.