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SCN populations high in dry year

SCN populations high in dry year

SCN on roots

Drought in 2020 didn’t only affect crop production, but soybean cyst nematode populations as well.

In analyzing results from the annual SCN yield tests over the past year, Gregory Tylka, Iowa State University plant pathologist, said the dry conditions hit multiple testing sites and gave more insight into how the pests reproduce.

“It showed in lower yields, but the other twist with drought is that SCN reproduction ramps up,” Tylka said. “The nematode reproduces much better. Numbers increase much more quickly in drought soils.”

The northwest, northeast, central and southeast parts of the state showed increased populations. Tylka said sandier soils, or soils that don’t hold water well, tend to see increased numbers of SCN.

While varieties with Peking resistance performed well again in 2020, he said the difference between that and the traditional PI-88788 resistance was not as large this season.

“I looked at all nine experiments we did in 2020 and the Peking varieties were in the top 10% in every one of those locations,” Tylka said. “In general, they continued to do well, but they didn’t have the extreme example like last year.”

Peking resistance still remains small in the marketplace, but Tylka said 2020’s tests saw 16 different varieties, the most in any testing season. He said in their southern Iowa testing sites, there was only one variety that contained Peking, so the market still needs to add diversity.

“We are suffering from this problem that SCN in Iowa has built the ability to reproduce on PI-88788, so farmers should seek out the Peking varieties to grow in rotation with the 88788 variety,” Tylka said.

He noted that the reputation of the Peking variety soybeans is for lower yields, but with increasing SCN populations, yields are starting to drag on the traditional varieties, making it worth looking at a switch. He strongly suggested inquiring with seed dealers about that option.

Tylka also pointed out a new resistance variety, PI89772 resistance from Northrup King — S23-G5X — which performed well in its initial tests.

“I don’t normally point out individual varieties, but this is a very unique variety,” Tylka said. “We had it in six of nine locations and it was in the top third to top half of yields. In north central (Iowa) it was the seventh highest out of 72. I would say it has a good start and they should only improve it.”

As farmers look ahead, Tylka said switching to corn for a year isn’t likely to reduce SCN populations. He said that means if a producer had high populations at the end of 2020 and goes into a rotation, expect numbers to stay high for 2022.

The Iowa State University test is funded by the soybean checkoff and the Iowa Soybean Association, as well as the United Soybean Board. Tylka said their help is critical, and he also thanked the soybean farmers who help with the research.

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