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View from the Cab: Know your risk

By: Kent Casson

Those high input prices with limited fertilizer availability have a few growers wanting to plant soybeans back-to-back, but experts urge caution.

After many experienced warmer growing conditions in 2021, fields infested with soybean cyst nematode could result in negative economic and agronomic impacts. Information from 15 years of trial experiments in Iowa indicated increased reproduction of SCN populations which can decrease yield by up to 14 bushels per acre. This represents a 23-percent yield loss.

“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,” warns Iowa State University nematologist Greg Tylka.

A recent multiyear study by researchers at the University of Wisconsin provides more reason for concern. This study compared corn and soybean rotations to corn on corn and soybean on soybean rotations. The traditional corn and soybean rotation produced greater yields than continuous planting of either crop. SCN population densities were greater in consecutive years of soybeans versus rotating with a non-host crop like corn.

“These results were not surprising,” notes Shawn Conley, a UW professor of agronomy. “They certainly reinforce the SCN Coalition’s recommendation to rotate SCN infested fields with a non-host crop.”

Soybean cyst nematode remains in the soil even when a crop is not present and is widely distributed, according to University of Kentucky plant pathologist Carl Bradley. The condition can be deceiving as soybeans typically look healthy above the ground despite the damage being done below ground.

“If you planted soybeans in 2021, the odds are high that SCN was present in that field and if soybeans were grown in 2022, SCN population densities will rise, resulting in a larger yield impact,” explains Bradley. “That’s why the SCN Coalition recommends rotating to a non-host crop like corn or wheat.”

The coalition experts also recommend soybean growers rotate SCN-resistant soybean varieties. If a PI 88788-resistant soybean variety was planted in the last rotation, you should next plant a variety with SCN resistance from Peking or PI 89772.


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