Extension and Ag Research News

Accessibility


Monitoring Important for Soybean Fields

The key to soybean management is to minimize plant stress during the R4 to R6 growth stages.

Like other crops, the planting and establishment of soybean fields was a challenge this spring because of the adverse weather and soil conditions.

In June and early July, soybean growth was slow, but that has changed positively during the last half of July and early August.

Soybeans are in the reproductive stages, with most fields in the full-flower (R2 stage) to pod development stages (R3 to R4).

Greg Endres, North Dakota State University Extension Service area agronomist at the Carrington Research Extension Center, has some reminders regarding soybean development stages and associated management strategies.

Soybean fields began to flower in early July. Flowering normally continues for about a month, until the early R5 stage (beginning of seed development). Pod development begins at the R3 stage (pod is 3/16 inch long at one of the four uppermost nodes on the main stem with a fully developed leaf) about two weeks after initial flowering. Seed development (R5 stage) typically begins about four weeks after initial flowering. Beginning seed maturity (R7 stage – one normal pod on the main stem reaching its mature pod color) averages about nine weeks after initial flowering.

“Obviously, growth stages overlap, but the key to soybean management is to minimize plant stress during the R4 to R6 growth stages (pod is 3/4 inch long to pod containing a green seed that fills the pod cavity at one of the four uppermost nodes of the main stem) to maintain high potential for seed yield,” Endres says. “This period starts about three weeks after initial flowering and lasts three to four weeks.”

Here are some management considerations during the balance of the season:

  • For late-planted Roundup Ready fields, glyphosate needs to be applied before the R3 stage (initial pod formation).
  • Watch for soybean aphids. Frequently monitor fields (at least once per week) to determine population levels and trends for timely control (based on university recommendations). Aphid scouting and control can cease at the R6 stage.
  • Defoliation by hail, wind or insects will have the greatest negative impact on yield during the critical reproductive stages (R4 to R6).
  • Bacterial and fungal diseases can be found in soybeans, and adverse weather (hail and high winds) have damaged fields, so numerous special foliar inputs are being marketed, including fungicides, nutrient mixtures and growth promoters (and combinations). However, NDSU studies indicate few and inconsistent yield increases with the use of these special products for trying to correct problems or improving plant productivity, so the return on investment is questionable.

“With more cooperative weather, combined with good management during these final six to eight weeks of plant development, we can look forward to a positive soybean harvest,” Endres says.

More details on soybean development and management strategies are available by contacting NDSU Extension Service crop specialists. Also, the NDSU “Soybean Production Field Guide” is available at http://www.ag.ndsu.edu/pubs/plantsci/rowcrops/a1172.pdf or can be obtained from the NDSU Distribution Center. Call (701) 231-7882 or email NDSU.DistributionCenter@ndsu.edu for information or order online at www.ag.ndsu.edu/pubs.

Another publication, “Soybean Growth and Development,” is available through Iowa State University by calling (515) 294-5247.


NDSU Agriculture Communication

Source:Greg Endres, (701) 652-2951, gregory.endres@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
Creative Commons License
Feel free to use and share this content, but please do so under the conditions of our Creative Commons license and our Rules for Use. Thanks.