SCN testing is critical

Published on April 4, 2020

University of Missouri Extension Plant Pathologist Kaitlyn Bissonnette tells growers it is critical to test for soybean cyst nematode (SCN) in the spring before planting.

            She notes data from the University of Missouri shows SCN field populations are becoming more virulent on commercial soybean cultivars. 

            “Easily transported by nature, SCN cysts and eggs can be spread within a field or to new fields by soil, equipment, water or wind,” says Bissonnette.  “Today, SCN is the top soybean disease in the U.S. and Canada.” 

Lifecycle of SCN

            SCN is a parasitic roundworm.

            According to Loren Giesler, University of Nebraska-Lincoln Extension plant pathologist, there are three main stages to the life cycle of SCN.

            “The cycle starts in the spring when temperature and moisture levels are adequate for egg hatch to release the juvenile nematode,” says Giesler. “Once a juvenile penetrates a soybean root, it moves through the root to the vascular tissue, where the nematode establishes a feeding site. It then continues to feed and swell, and eventually the females burst through the root tissue.” 

            Giesler explains the majority of eggs are produced inside the female’s body, while some are produced on the outside. 

            “The eggs on the outside of the body hatch and the juvenile nematodes re-infect the soybean roots,” she says. “The egg-filled body of the dead female is what we call a cyst. Each cyst can contain up to 400 eggs.” 

            Gielser notes there can be three to four generations of SCN in a single growing season.

Effects of SCN

            According to the SCN Coalition, a private-public partnership of researchers, Extension specialists and industry representatives, soybean yields can drop as much as 14 bushels per acre in fields infected with SCN when reproduction is high. 

            “Populations can increase exponentially, with 100 females capable of producing 39,062 eggs after four generations in one growing season,” says the coalition 

            Bissonnette notes SCN is difficult to detect without testing because damage occurs to the root system before it can be seen.

            “Symptoms include stunted plants, yellowing and yield loss,” she says. “Yield loss can occur even when there are no visual symptoms.” 

            According to Gielser, these aboveground symptoms may be confused with damage from compaction, nutrient deficiencies, drought stress, low-lying wet areas, herbicide injury and other plant diseases.

Testing for SCN

            There are two ways Bissonnette suggests growers test for SCN. 

            “The first method is to dig up a month-old soybean plant, gently shake the soil from the roots and look for white females,” Bissonnette says. “The second method is to collect soil samples for testing.” 

            If growers choose to collect soil samples, Bissonnette recommends they collect 15 to 20 core samples for every 20 acres. She also notes cores should be six to eight inches deep and an inch in diameter. 

            “Collect them in a zigzag pattern and divide each field into management zones,” she says. “Include high-risk areas such as the field entry, flooded areas, low spots and historically low-yielding zones.” 

            For each collection zone, Bissonnette says growers should mix the core samples together.

            “Moisture content is critical,” she states. “Ideally, cores will stay intact during collection but will easily fall apart upon mixing. When in doubt, err on the dry side.” 

            Bissonnette says growers should put their soil samples in a labeled bag. She also recommends marking down the GPS coordinates of the field where the samples were collected, if possible. After this, growers can send their samples to a testing facility.

            “Growers need to know their baseline SCN egg count and test every three to five years,” explains Bissonnette. “Comparing SCN egg counts tells growers if their management plan is working or not.” 

            Bissonnette also recommends growers work with crop advisers and Extension agronomists to develop a management plan which may include crop rotation and using nematode-protectant seed treatment.

            Information in this article was compiled from an article in Missouri Farmer Today titled Test in Spring to Track Soybean Cyst Nematode Success and a University of Nebraska-Lincoln article titled Soybean Cyst Nematode.

            Hannah Bugas is the assistant editor for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.