This article was updated in 2025.

Pre-harvest is the ideal time to get into the field and evaluate your soybean crop. Taking stock of final harvest population as well as disease and weed pressure will give you important intel to set you up for success in future seasons. 

Marijke Vanderlaan, Agronomic Service Representative for Syngenta, encourages growers to not only do assessments before harvest, but to also get into your fields even earlier for additional detective work. “Get out there at R7 prior to leaf drop for additional clues on potential issues. Once you’ve harvested the field, trying to guess the issue that may have prevented you from maximizing yield is much tougher.”

Double-check your population

Vanderlaan says the first thing to evaluate is your final harvest population.

“If you planted 160,000 seeds in the spring and there’s a big variance, do some investigation to understand the reason for it,” she says. “Check if your plant spacing is even. If you’re in 20- or 30-inch rows, did the variety reach full canopy? Because then we know we’ve got maximum photosynthesis and better yield potential.”

Look for disease challenges

Something else to look for are areas that have been challenged by disease. Be aware of parts of the field that didn’t perform as well as you expected. Ask yourself: ‘What happened that limited my yield here?’”

“Let's say there’s a low spot in the field where a number of the plants have died. It could be the result of phytophora, soybean cyst nematode or some other yield-robbing disease,” says Vanderlaan. “Try to identify what’s going on in the affected area. Could it be white mould or sudden death syndrome (SDS)? All of these diseases are easier to diagnose when leaves are still on the plant.” She suggests if you can’t discern what it is right then and there, mark it on a map as a problem area and follow up.

Fortunately, strategic variety selection and quality seed treatment will help ensure that those diseases won’t steal yield from future bean crops. Saltro^® seed treatment, for example, has been a proven solution on the market for a few years to help guard against early-season SDS infection.

Watch for weeds 

Weeds are another watch-out in your soybean’s pre-harvest. Take the time to evaluate how your overall weed control program performed this season. “If weeds are present pre-harvest, did they come in after the critical weed-free period when the effect on yield isn't as significant?”
 
“I see enough weed escapes out there, like fleabane and grasses” says Marijke. “It's because many growers are still just using one or two shots of glyphosate for their grass control.” She suggests it's best to apply a residual like Boundary^® LQD on Xtend^®, XtendFlex^® or Enlist^® soybeans. Tavium^® plus VaporGrip^® Technology is a great option too on the Xtend or Xtendflex traited beans.

Vanderlaan also advises to be on the look-out for problem weeds like the expanding waterhemp. “It’s currently resistant to 4 different modes of action (2, 5, 9, 14) and looks very similar to pigweed. If unchecked or undiagnosed, significant yield losses and harvest issues can occur” she says. Tavium^® plus VaporGrip^® Technology herbicide is a good choice. “It helps suppress the grasses, and you also have a couple modes of action to target waterhemp.”

If you’re seeing a lot of winter annuals or perennials such as dandelions during your pre-harvest check, Vanderlaan recommends planning a fall burndown. “Typically, the best time to control those weeds is in the fall” she says.

Check your pods

Something else to check in the crop is overall pod size and number of beans per pod. “In some years, you might find gaps at several nodes somewhere along the plant,” says Vanderlaan. “If so, what were the issues going on at that time in the season that caused it to abort those pods?” Drought stress, water stress, excessive heat could all be potential culprits.

Take note

Think back on your season as you’re checking out your soon-to-be harvested beans. Did your crop experience some of the issues that Marijke has highlighted? “In some cases, we are talking 10 to 50 percent yield loss in those specific areas where these pests and diseases are a problem,” she says. After your pre-harvest investigation is complete, be sure to record some notes to help you capture the full potential of your soybeans in future seasons.

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