Growers still contemplating planting late-season beans should get them in the ground as soon as possible to avoid reductions in yield potential, according to Clemson University Agronomist Pawel Wiatrak.

PAWEL WIATRAK, Clemson University agronomist, checks yield potential of different maturity group soybeans planted late in tests at the Edisto Research and Education Center near Blackville, S.C.

Yield reduction has long been an issue for double-crop beans in the Upper Southeast. New varieties and the recent high prices for soybeans have helped growers attack yield drag in a positive way. The stakes are high in terms of increased production costs and reduced plant performance.

Wiatrak tested soybeans from Maturity Group IV through Maturity Group VIII at varying planting dates and says beans planted by May 20 produced the highest yields, regardless of Maturity Group. Not counting Maturity Group IV beans, which have not performed consistently well in the Clemson tests, beans planted from early to late-May consistently produced 55 bushels per acre and frequently topped 60 bushels per acre under dryland conditions.

For early June planting date, yields ranged from about 40-50 bushels. Not only was yield reduced, but yields were also much less uniform in the later planted soybeans.

Extending the planting date to late-June, yield was cut to about 30 bushels per acre. The wet spring across the Carolinas delayed wheat harvest this year and will no doubt take a toll on statewide soybean plantings and yields, the South Carolina researcher says.

For growers still considering planting beans into July, the yield will be significantly reduced. Wiatrak, says cutting input costs in late-planted beans will further cut into production capabilities of the soybean plant and subsequent value of the crop.

However, based on preliminary testing, Wiatrak says Maturity Group VIII soybeans planted in July produced about 30 bushels per acre. He says, if a grower has to plant soybeans in July, Group VIII varieties would be the optimum.

Even at about 30 bushels per acre soybeans can be profitable, according to recent research at North Carolina State University — if wheat yields are good.

Getting double crop beans planted as soon as possible after wheat is harvested will significantly help to increase yield potential. Late planted soybeans try to compensate for the shorter growing season, exposing the plant to a number of crop stresses that can reduce yield.

Early weed control is important in any crop, but the pressure to get double-crop soybeans in the ground and up and growing quickly makes the transition from wheat to soybeans especially critical. Wiatrak points out that every day counts and every production practice counts in terms of yield losses when soybeans are planted past the critical June 5-10 date.

Later planted soybeans are more susceptible to weed pressure because the environment is better for growth. In earlier plantings, soybeans are better equipped to compete with weeds, but the higher soil temperatures in late June and into July create a much better environment for weeds to germinate and create more competition for young soybean plants.

“In South Carolina, our soybean growers have to pay special attention to pigweed, because so many have developed resistance to glyphosate. Burning down weeds after wheat harvest with glyphosate is quick and efficient, but it can create major problems for late-planted soybeans, if there are resistant pigweeds in the field,” Wiatrak stresses.

Late planted soybeans will also require a higher seeding rate to maintain a yield potential comparable to full season beans. If soybeans are planted by early-June, seeding rates of about 82,500 are usually sufficient under optimum planting conditions. Soybeans planted after June 5, should maintain seeding rates of about 110,000 seeds per acre.

A soybean crop will produce approximately 2 bushels per acre for every inch of water it uses through the season. Yields in the 40 to 50 bushel per acre range require 20 to 25 inches of available soil moisture during the growing season. The irrigation water needed will vary depending on the beginning soil moisture and the rainfall received during the growing season. An irrigation system needs to be capable of providing 10 to 15 inches of water during the season to assure an acceptable yield.

For growers using irrigation to reduce yield drag on double-crop soybeans, it is critical to know that beans need more than twice as much water during rapid vegetative growth up to pod fill and full canopy as they need in the early growth stage and late pod maturity stages. Timing of irrigation on July-planted beans is especially critical because rain patterns tend to favor earlier planting dates and increased temperatures during critical times on late planted beans up the ante on timeliness.

Once you get past early June, every day makes a difference in what maturity group, variety, and production practices you use — the results are heightened with every day planting is delayed. When you move into July, the risks go up even higher. Wiatrak stresses that Group VIII maturity beans have a higher leaf area, giving them some significant advantages over other maturity groups.

In general, timing of pesticide applications on late-planted beans, along with other production practices are more critical on late-planted soybeans. Despite the across-the-board risks involved in planting soybeans as late as the end of June, the double-crop value with wheat or barley can be worth the risk.

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