Many factors contribute to high-yielding soybeans. Variety selection, crop nutrition and disease and weed control are just some of the variables that can make or break a crop.

Growers have to make management and input decisions throughout the growing season to help their crop reach its yield potential. Many of these decisions have a direct correlation to crop development, says Syngenta Canada Agronomic Services Representative Marijke Vanderlaan. That’s why having a strong understanding of the Soybean Critical Growth Stages is fundamental for mastering soybean management.

When discussing critical growth stages, Vanderlaan reminds growers that they have to keep a close eye on their crop throughout the season, including both the vegetative (V) and reproductive (R) stages.
 
“When we plant certified, treated seed we’re entering the Vegetative Emergence (VE) stage,” says Vanderlaan. “This is where we want to see strong germination and even emergence, which is critical for effective stand establishment and achieving targeted plant populations.” 

Seed protection and weed control

The VE stage is where growers get to apply much of the field and management knowledge they have accumulated. Seed and trait selection and seed treatments should be based on their knowledge of the agronomics and history of the field, notes Vanderlaan. “Are you planting early? Is there a history of Phytophthora or Pythium? These are all factors that need to be considered when choosing seed treatments such as Vibrance^® Maxx, Apron XL^® or Saltro^® that will help your crop emerge and maintain yield potential.”

The seed treatment decision also includes controlling insects and pests. A product like Cruiser Maxx^® Vibrance Beans will help protect against pests such as wireworms and seed corn maggot. 

Vanderlaan adds that V1 is also the beginning of the critical weed-free period (V1 to V3) in soybeans. If the field is not clean at this point growers can be losing 0.5 to 2 bushels per day for each day that weeds are not controlled.

Applying a pre-emerge residual herbicide is a good strategy to manage this yield risk. Pre-emerge soybean herbicides offer more options in the way of active ingredients and spectrum of weed control. Growers then also have the option of using a post-emerge herbicide should they need to clean up escapes and second flushes.

Timing fungicide to fight disease

Soybeans then move into the reproductive (R) stages where disease control and fungicide application become vitally important. The first concern is disease control, specifically white mould. Vanderlaan says this can be a confusing time for soybean staging. Here, growers with a field history of white mould or high-risk environmental conditions (cool, wet weather and lush canopy), need to zero in on the R1 to R2 stage.

Some agronomists recommend spraying for white mould at R1 (appearance of first flower at the 4th trifoliate near the summer solstice) but that’s a little too early for fungicide unless the weather is highly conducive to white mould, notes Vanderlaan. “Typically, it’s more around R1.5 where we really want to think about that white mould fungicide,” but she adds that this application window can extend up to R2.5. “We need to get those petals covered to prevent them from becoming infected and then falling into the nodes and infecting them.”

At this point, growers can opt for a white mould fungicide like Allegro^®. Vanderlaan notes that a two-pass program makes a lot of sense for growers in heavy-pressure areas. “You make your first pass when you have several flowers up the main stem and then a second pass, 10 to 14 days later. That has a high return on investment when Mother Nature is favouring white mould.”

If growers are targeting a single fungicide application to control Septoria and pod and stem blight, they need to focus timing on the R2 stage with a product like Trivapro^®.

Late-season management tips

When it comes to crop nutrition, Vanderlaan says soybeans respond to fertile soils and adding starter fertilizer gives growers an opportunity to get their crop off to a good start. She notes that soybeans fix their own nitrogen but there’s growing evidence that applying nitrogen later in the season — between the R4 to R6 bean fill phase — can enhance yields. “We’ll watch for more research in this area. That could prove to be a nice opportunity for growers pushing for higher yields.”

The next growth stage Vanderlaan advises growers to focus on is R6.5 or physiological maturity. Here pre-harvest burndown and desiccation product choices are important, depending on whether the crop is identity preserved or heading to a commodity market.

The season wraps up at R8 when the crop is ready for harvest. At this stage, Vanderlaan points out that there are often key management insights to glean from a pre-harvest scout and the view from the combine. 

“Keep an eye out for lodging or leaning in your beans. It might be an indication of a seeding rate that’s too high. Potentially, it could also be a disease-related issue, especially if you didn’t apply a fungicide,” says Vanderlaan. “That’s the type of information that can help better manage future soybeans crops in those fields and produce higher yields.”