Evaluate soybean emergence, stands

JOHNSTON, Iowa — Emergence is a critical time to be scouting and evaluating soybean stands to ensure the crop is set up for success.

John Schoenhals, Pioneer field agronomist, provided some guidance on what to look for when scouting young soybean plants.

Singularity and uniform emergence is important, so make sure to apply fungicide where needed, scout for pest and disease pressure and keep an eye out for injury from pre-emergence herbicide, Schoenhals said.

“Check plant roots and hypocotyls for disease or insect damage. Also, if the field receives a heavy rain at around emergence, splashing injury may be visible,” he said.

“While plants may outgrow these symptoms, severe damage can cause stand loss or create opportunity for seedling blight pathogens that impact the plant.

“Also, when evaluating stands impacted by frost events, make sure to check for growth from auxiliary buds rather than only looking at the color of the cotyledons.”

Populations

To check soybean populations, Schoenhals uses a hula hoop for drilled soybeans and a tape measure for planted soybeans.

“When using a hula hoop for drilled soybeans, use a multiplication factor for the size of the hula hoop you are using. For example, for a hula hoop with a 26-inch inside diameter, the multiplication factor is times 11,800,” he said.

For example, if 14 plants are counted within the 26-inch hoop, that would multiple out to 165,200 plants per acre.

“For planted soybeans, measure the appropriate distance for one ten-thousandths of an acre, count the plants and multiply by 10,000,” Schoenhals said. “These estimates might not be very exact, but if conducted in several spots they give a very good indication of surviving stand.”

For 15-inch planted soybeans, 16 plants are counted along 42 inches of row, resulting in 160,000 plants per acre, for example.

Replant Considerations

Soybeans have tremendous ability to compensate for reductions in stand if uniformity is somewhat consistent.

“If a stand has been entirely lost as may be the case where water ponded for several days, replanting is needed. But until stands are reduced below 80,000 to 90,000 plants per acre, adding to thin stands may not provide a yield advantage,” Schoenhals said.

“Of course, there are exceptions to these recommendations. Some soil types such as heavy clays and sands may need a greater final population in order to shade the ground and achieve acceptable yields. Also, keep in mind that weed control can become more difficult to achieve when stands are reduced.”