Think Twice Before Replanting Soybeans March 4th, 2014

Date: March 4, 2014
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Linda Funk
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Think Twice Before Replanting Soybeans

Think Twice Before Replanting Soybeans

Madison, WI, March 4, 2014 —Inclement weather coupled with insect or disease pressure associated with spring planting sometimes can require replanting of soybeans. However, a Wisconsin soybean researcher says farmers may want to make some considerations before investing in replanting soybeans.

“Research is finding that similar yields among reduced plant stands due to the soybean plants compensatory ability and diminished yield potential of replanted or later planted soybeans are reasons that farmers may want to consider not replanting,” says Shawn Conley, state soybean specialist for the University of Wisconsin-Madison.

A study was conducted in 2012 and 2013 at the Arlington Agricultural Research Station, Arlington, WI on replanting. Twelve different replant scenarios were planted in 15 inch rows during early May, late May, and mid-June. The replanted portions of the plots were in­terseeded between the rows of the initial soybean stand. ApronMaxx RFC and Cruiser­Maxx (Syngenta Crop Protection) seed treatments were used to compare a fungicide only seed treatment with one that also contains an insecticide.

Objectives of the research was to determine the threshold for replanting soybean stands, evaluate replanting options and quantify the effect of seed treatments and planting date on replant decisions.

Determine the Initial Plant Stand

The first step in making an informed replant decision is determining the initial plant stand. Soybean stands can be deceiving to the eye sometimes, especially in narrow rows (<15 inch), where stands can be greatly underestimated. Therefore, using the hula hoop method or counting the number of plants in a row is needed to accurately determine the plant stand. If severe weather causes stand reduction and/or plant injury, stand counts should be performed 3-5 days after damage has occurred to give the plants time to recover. Only live plants that are expected to survive should be counted.

Replant Threshold

“Our study demonstrated that replanting soybean stands below the threshold (100,000 plants/a) by filling in the existing stand, increased yields regardless of the date (May- June 20th) and seed treatment use,” Conley says. “Below threshold plant stands should be filled in with enough seed to bring the final stand above 100,000 plants/a. Using tillage and replanting the entire stand greatly limited yield potential, even at replant seeding rates of 220,000 seeds/a. This is due to the entire plant stand being replanted or essentially planted later, which reduces yields by 0.32 bu/a/day on average. These replant recom­mendations are applicable through June 20th in southern WI, where replanting after this date is not advised.

“Traditionally, the notion of adequate weed control has led producers to desire higher plant stands to quickly shade out competing weeds,” Conley says. “However, pre-herbicide use and modern post herbicide technology has essentially eliminated this concern. This study only evaluated soybean replanting in terms of yield and did not take into account the economics of a replant decision, which include additional seed, fuel, labor, and machinery costs; along with potential crop insurance replant payments. Pro­ducers should consult their crop insurance agent before making any replant decisions. Ultimately, the producer’s efforts should be placed on using this data in conjunction with their own finances to determine if replanting will increase economic return.”

For more information on this research, go to