With corn grain prices being down, some producers may 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," said Emmanuel Byamukama, SDSU Extension plant pathologist.
If planting soybeans into a field that was under soybeans last year be the plan for the 2015 growing season, Byamukama said 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 explained. "This means that planting soybeans in a non-rotated field may increase the risk of these diseases to develop."
If a soybean field has had a history of moderate to severe disease development, Byamukama encouraged growers to be careful in their cultivar selection. While resistance to many soybean diseases may not yet be available, Byamukama explained 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).
"One particular soybean production constraint that needs to be assessed carefully before planting soybeans following soybeans is SCN," explained Connie Strunk, SDSU Extension plant pathology field specialist.
In non-rotated fields with a history of SCN, Strunk said this nematode problem can increase to reach damaging levels.
She encouraged producers to test their soils before planting soybeans-on-soybeans.
For South Dakota growers, free SCN testing courtesy of South Dakota Soybean Research and Promotion Council is available. 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 said. She added 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 said it is important to keep testing soils to monitor SCN build up in the field. "If SCN numbers keep on rising, this would mean SCN intervention methods being applied are not working," she said. "Therefore, longer rotations out of soybeans and change in SCN resistant cultivars would be recommended."
Seed treatment may be another disease management strategy that producers planning soybeans-on-soybeans may want to consider, Byamukama said. "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 said.
He added 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 said.
In making crop rotation decisions, producers may 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.