Soybean cyst nematodes are common in many Iowa fields. One way to check fields for this yield-robbing pest is to dig soybean roots and look for the small, round, white adult SCN females. Typically, growers can expect to find females appearing on soybean plant roots about six weeks after planting. But this year the female nematodes started showing up in fields in early June, in some cases in as little as 26 days after planting.
“We tested some soil samples during the first week of June that already had egg counts ranging from 1,100 to over 5,000,” says Jim Friedericks, outreach and education director at AgSource Laboratories. “That’s much higher than we would expect to find at this early stage in the season.”
Extension staff at Iowa State University suggest that this early development of the nematode females is likely due to the unusually warm temperatures Iowa had in May. The concern with this early appearance is there will be more generations of nematodes this summer, resulting in higher populations and the potential for high cyst and egg counts this fall.
Plan your strategy
Knowing the level of SCN pressure this year is important so that proper plans can be made to include more non-host and resistant crops in the rotation, and other control measures in the years to come if needed.
When SCN counts in a field increase to over 2,000 eggs per 100cc soil, AgSource Laboratories recommends beginning a six-year rotation that includes a non-host crop and alternating soybean varieties with PI8878 and Peking SCN resistance. Sampling for nematodes is typically done in the fall. But if you are suspicious of already high infestations, a sample collected in the summer will provide reliable information.
“Managing SCN can be difficult since no single tactic will control SCN,” Friedericks says. “But using several management strategies can help minimize yield loss.”
Follow soil sampling instructions
Soil samples can be taken anytime during the year; however, it makes the most sense to sample fields for SCN in the fall, just prior to harvest. Friedericks offers these guidelines:
• To effectively check fields for presence of SCN, soil must be collected from no more than a 20-acre section, collecting a composite sample of 10 to 20 soil cores.
• Higher risk areas, where SCN may first appear, could include areas near a field driveway, along fencelines or where weed control is poor, in low areas that may have been flooded and in areas of the field where soil pH is above 7.
• Mix the soil cores very well and place in a tightly closed soil bag.
• Keep the samples at room temperature or cooler, and out of sunlight until they can be shipped to a lab for testing. The results will be shown as eggs or cysts per 100 cc of soil. AgSource Laboratories tests soil for nematodes and offers both cyst and egg counts.
Additional information is available from Iowa State University Extension at plantpath.iastate.edu/scn.
Source: AgSource Labs