BROOKINGS, S.D. -- With corn grain prices down, some producers might be considering planting soybeans on soybeans because of economic reasons.
"Soybean does not require heavy inputs such as fertilizer, and soybean grain prices have not taken such a big hit as corn," says Emmanuel Byamukama, South Dakota State University Extension plant pathologist.
If planting soybeans into a field that was under soybeans last year is the plan for the 2015 growing season, Byamukama says producers need to be aware of disease risks and should plan ahead to minimize negative impacts of these diseases on soybean yield.
"The majority of soybean diseases in South Dakota are either residue-borne or because pathogens survive in the soil," he explains. "This means that planting soybeans in a non rotated field may increase the risk of these diseases to develop."
If a soybean field has a history of moderate to severe disease development, Byamukama encourages growers to be careful in their cultivar selection. While resistance to many soybean diseases might not yet be available, Byamukama explains that seed companies do provide disease ratings for soybean cultivars for several pathogens including Phytopthora root rot, white mold, brown stem rot, sudden death syndrome and soybean cyst nematode (SCN).
ADVERTISEMENT
"One particular soybean production constraint that needs to be assessed carefully before planting soybeans following soybeans is SCN," says Connie Strunk, SDSU Extension plant pathology field specialist.
In non rotated fields with a history of SCN, Strunk says this nematode problem can increase to reach damaging levels.
She encourages producers to test their soils before planting soybeans on soybeans.
Testing for SCN is free of charge, courtesy of the South Dakota Soybean Research and Promotion Council.
"There is still time to test soils before soybean planting this year," Strunk says.
She adds that soil sampling for SCN can be done anytime provided the soil is not frozen or too wet.
"Knowing the status of SCN in a field will help in deciding the need for SCN-resistant cultivars."
For fields with a history of SCN, Strunk says it is important to keep testing soils to monitor SCN build up in the field.
ADVERTISEMENT
"If SCN numbers keep on rising, this would mean SCN intervention methods being applied are not working," she says. "Therefore, longer rotations out of soybeans and change in SCN resistant cultivars would be recommended."
Seed treatment could be another disease management strategy that producers planning soybeans-on-soybeans might want to consider, Byamukama says.
"Especially for fields with a history of soybean stand establishment problems. Although pathogens causing seedling diseases in soybeans can survive in soil for several years, soybeans following soybeans have increased level of inoculum in the soil," he says.
He adds that for foliar diseases where resistance is not available (e.g. brown spot, frogeye leaf spot, downy mildew), early scouting for disease pressure and applying a timely fungicide application will protect yield.
"Research conducted at SDSU and other universities in the region indicate a higher probability of return on investment when foliar fungicide application is done under significant disease pressure before or at R3 growth stage coupled with relatively wet weather conditions," Byamukama says.
In making crop rotation decisions, producers might want to consider long term profitability of a crop rather than focusing on one season's profit. Decisions made in one season may affect the productivity and therefore profitability, of the crop in multiple upcoming seasons.
