COLUMBIA, Mo. – Soggy fields, low soil temperatures and 16 cloudy days in May delayed soybean planting in Missouri.

Average yield for soybean planted in the third week of June is at least 25% less than soybean planted in early May, and July plantings fare even worse, says University of Missouri Extension soybean specialist Bill Wiebold.

But Wiebold says farmers can use proven management practices to add a little extra yield to late-planted soybean, now selling in the $14-$15 per bushel range.

Wiebold’s data on ultra-late-planted soybean tracked crops planted in mid-Missouri plots in 2009, 2010, 2016 and 2017. The data shows 2009 yields dropped from nearly 80 bushels per acre when planted by mid-May to the high 20s when planting was delayed to July 20. In 2017, yields dropped from the mid-40s when planted in the second week of May to 8 bushels when planted July 19. Yields in 2010 and 2016 fell about one-third when planting was pushed back to July 16 and July 21, respectively.

His data shows that growers can still expect yields of 25-30 bushels per acre even when soybean is planted in late July – if the weather cooperates. “The probability of a weather challenge increases with delayed planting,” Wielbold says.

Late-planted soybean can run out of time and favorable weather. This happened in 2017, when a killing frost before harvest resulted in the dismal 8-bushels-per-acre yield on soybean planted July 19 in Wiebold’s plots.

Late-planted soybean also have less time to capture sunlight. Shorter daylight periods lessen seed fill and result in smaller plants with fewer nodes. Late plantings also produce fewer soybean branches where pods form.

The number of main stem nodes declines as much as 650,000 nodes per acre for each day planting is delayed. Another 40,000 plants per acre are needed when planting in mid-July.

Wiebold’s other recommendations:

• Plant in narrow rows. This allows plants to capture available sunlight sooner in a shortened growing season.

• Use no-till planting.

• Increase seeding rate. Late-planted soybean produce fewer main stem nodes and smaller branches. Boost the seeding rate by at least 30,000 seeds per acre to increase plant numbers. In late-planted soybean, stand density should be at least 150,000 plants per acre. If using a grain drill, consider increasing the seeding rate because drills are challenged to control seed depth and closure.

• Monitor soil conditions to limit compaction. Carefully adjust the planter to reduce compaction near the seed to provide the best environment for early root growth.

• Treat seeds with a fungicide. Seed treatments, especially fungicides that protect against Pythium and other fungi, aid stand establishment and early vigor to improve yield potential during the shortened season.

• Stay with your normal maturity group.