AGVISE Laboratories has been doing soybean cyst nematode (SCN) testing at our Benson, Minnesota, laboratory for four years. There has been a large increase in the number of SCN samples in the last two years, apparently due to nematodes occurring over a larger area as soybean acres increase. Laboratory equipment and techniques have been evolving as the researchers have been developing more accurate and consistent procedures. Sampling for SCN can be very difficult due to the extreme variability of nematode populations within a field. This is especially true when the SCN density is low. Hot spots may test very high, and other areas of a field may test zero eggs. Examining roots in late June and early July for SCN females, along with a SCN soil test, is a good method for determining the level of infestation. SCN symptoms can be similar to iron chlorosis symptoms at times, but SCN symptoms usually occur in late June to early July, and iron chlorosis usually shows up in early June. Soil testing the hot spots in a field will help you determine the presence or absence of SCN, along with the root examination during the mid-summer months.
Based upon University of Minnesota research, they use the following guidelines based upon nematode egg counts:
- < 200 eggs/100 cc of soil: Plant a susceptible variety.
- 200 – 2,000 eggs/100 cc: Plant a resistant variety.
- 2,000 – 10,000 eggs/100 cc: Resistant variety recommended, but yield loss may still occur.
- > 10,000 eggs/100 cc: Resistant or susceptible variety should not be planted.
Rotation Management Strategies If SCN Detected
Year 1 – Corn or other non-host crop such as small grains or alfalfa
Year 2 – SCN resistant variety (PI 88788 or Peking resistance source)
Year 3 – Corn or other non-host crop
Year 4 – SCN resistant variety (resistance source different than year 2 variety)
Year 5 – Corn or other non-host crop
Year 6 – Susceptible soybean variety
Continue to monitor for the level of SCN in your growers’ fields.