By Angie Peltier
Soybean cyst nematode (SCN) is a microscopic worm that is attracted to and infests soybean roots where it uses for its own growth and development the water and sugars that the soybean plant takes up to develop leaves, flowers, pods and beans. Capable of causing significant yield loss without alerting a producer of its presence, SCN caused an estimated $7.65 million in lost yield in 2022 in Minnesota (Crop Protection Network, 2023), making it the top yield-limiting pathogen of soybean in Minnesota and throughout the Midwest.
At certain points in the Minnesota soybean growing season, plants infested with SCN can be dug up and the soil gently shaken from the roots to reveal creamy, white, lemon-shaped, swollen female SCN (Figure). Much smaller and more uniform in size and shape than nitrogen fixing nodules, the female SCN darkens in color and dies with 200-250 eggs inside her as her body hardens to form a cyst. Cysts provide a bit of protection for the SCN eggs inside. Seeing the swollen female SCN can tell one that a field is indeed infested, but management recommendations are based on a field’s egg counts.
Know your numbers!
To estimate a field’s SCN population density, collect a composite soil sample. A composite sample is collected by taking small subsamples of soil 8 inches deep using a soil probe from 15-20 different spots from a field area no larger than 10-20 acres.
<200 eggs/100 cc soil
In less than half of a cup of soil, less than 200 eggs is considered low risk, and although SCN populations will grow considerably throughout the growing season, an SCN susceptible variety can be grown.
201 - 2000 eggs/100 cc soil
Egg densities between 201 and 2000 eggs/100 cc soil, yield loss would be expected when growing an SCN susceptible variety, and growing a resistant variety is recommended.
2001 - 10,000 eggs/100 cc soil
At egg densities between 2001 and 10,000/100 cc, some yield loss is expected even when growing an SCN resistant variety.
>10,000 eggs/100 cc soil
Soybean production is not recommended when egg counts are greater than 10,000/100 cc due to a prohibitively high yield loss potential. Growers should consider a crop other than soybeans until egg counts decrease in following years.
How to receive sampling supplies
In an effort to help Minnesota soybean producers to “know your numbers” the Minnesota Soybean Research & Promotion Council is sponsoring a fall 2023 SCN Sampling Program.Source : umn.edu