High SCN population densities from 2021 make beans on beans in 2022 a risky proposition

Farmers may be planning to grow soybeans in 2022 in fields cropped to soybeans in 2021 because of high prices and limited availability of inputs for corn production. Doing this in fields infested with the soybean cyst nematode (SCN) is always a risky proposition. But growing beans on beans in SCN-infested fields in 2022 will be especially dicey.

SCN reproduction is greater in hot, dry growing seasons, and many soil samples collected at harvest from field experiments in Iowa in 2021 have very high end-of-season SCN population densities. SCN eggs survive very well in the soil over winter, so high end-of-season SCN numbers in 2021 will affect soybean yields in 2022 and beyond. A recent ICM News article gives details of the very high SCN egg counts and the associated low soybean yields of SCN-resistant soybean varieties in one experiment in southeast Iowa in 2021.

Fields that will have soybeans grown for a second successive year in 2022 need to be sampled for SCN this fall. And a good use of limited inputs to grow corn in 2022 would be in fields with the greatest SCN population densities. Doing this will: 1) eliminate the risk of getting very low soybean yields due to SCN damage from growing beans on beans in 2022, and 2) reduce the SCN egg population density by 5-10% to as much as 50% in just one year, which will pay soybean yield dividends in 2023.

Also, soil samples should be collected from fields in which soybeans will be grown in 2022 following corn to determine the level of SCN present in the soil. Farmers should seek out and grow SCN-resistant soybean varieties with SCN resistance that is not from PI 88788 in fields with SCN egg population densities >5,000 eggs per 100 cm³ of soil because the SCN populations that live in most Iowa fields have developed increased reproduction (and thus cause increased yield loss) on varieties with PI 88788 resistance. Soybean varieties with resistance different from PI 88788 are listed in a recent ICM News article. Finally, farmers also should consider using effective nematode-protectant seed treatments on soybeans planted in SCN-infested fields in 2022.

There are guidelines for collecting soil samples this fall for SCN and information on where to send the samples for processing in a recent ICVM News article.