Watch for 6 soybean diseases in 2012
While it’s difficult to say exactly what diseases will be prevalent in Nebraska soybean fields in the upcoming growing season, University of Nebraska Extension plant pathologist, Loren Giesler, has the inside track on potential diseases to look for:
• Frogeye leaf spot. Giesler says that frogeye leaf spot has been more common in several areas over the past few years. It is recognized for its distinctive yellow eye-like spotted marks on soybean leaves. “If there is a history of frogeye in the field, farmers should note that fact and look at management practices, primarily rotation with corn and using resistant varieties,” Giesler says. “When we get into the season and see it at the R3 or flowering stage, a fungicide treatment has a likelihood of taking care of it.”
At a glance
• Frogeye leaf spot has been showing up in more fields every year.
• Root and stem rots are observed every year at some locations.
• Resistant varieties, crop rotations can avoid many disease problems.
• Phytophthora root and stem rot. In areas where there is high soil moisture content or rainfall after planting, phytophthora root and stem rot could show up. Giesler suggests that farmers who haven’t made their seed selection choices yet may want to consider a resistant variety in areas where there is a history of phytophthora. “If they haven’t made a choice on seed treatment, they can talk that over with their seed dealer to be sure the seed treatment is protective against phytophthora,” Giesler says. Generally, the southern half and eastern third of the state have more phytophthora, but the disease occurs in many areas of the state. It depends on the planting date and if rain is plentiful after planting.
• Brown stem rot. “We see some brown stem rot every year,” Giesler says. Infected plants may not show visible symptoms other than premature death. It is confirmed by splitting stems of infected plants, revealing internal browning of the pith and vascular tissue. Caused by a fungus that survives in plant residue, brown stem rot can be reduced “with crop rotation along with selection of resistant varieties,” Giesler says.
• Sclerotinia stem rot. Sclerotinia is seen at a few sites every year, Giesler says. “It is normally considered a minor problem, as it does not develop consistently across the state,” he says.
• Soybean cyst nematode. “This is definitely one that we still have awareness issues with,” he says. “And anywhere that was flooded this past season, if the field didn’t have SCN before, it may have it now.” SCN can float in water running over new fields. Controlled by planting resistant varieties, SCN can be identified in soil samples. Free sample bags and a sampling program are available to producers who bring their soil samples to a local UNL Extension office.
• Sudden death syndrome. Sometimes confused with brown stem rot, SDS is caused by soilborne fungus that overwinters in soil and residue. SDS normally displays chlorotic spots on leaves at R3 or later in the growth stages of the plant. As the symptoms advance, yellow spots cover the leaves and eventually the yellow areas become brown as the tissue dies from the toxins. Wet growing conditions on high-yielding ground, combined with compaction from harvest equipment the previous year, provide a perfect climate for SDS. Dry harvest conditions this past year may reduce the occurrence of this disease in 2012.
Giesler says that Asian soybean rust continues to be monitored, particularly in the Gulf States, but it hasn’t presented the problems that were initially expected, even under conditions that would be considered optimal for the spread of the disease.
This article published in the February, 2012 edition of NEBRASKA FARMER.