Research Highlights

Farmers Can Improve the Effectiveness and Yield of SCN Soybean Varieties

By Carol Brown

Farmers have been fighting soybean cyst nematode (SCN) for many years. A lot has been done to help farmers combat this disease, but it continues to be one of the leading yield suppressors of soybeans.

Marisol Quintanilla, an entomology professor at Michigan State University, is helping soybean farmers figure out ways to improve their yields while reducing SCN presence in their fields.

“Two soybean varieties commonly used by farmers, Peking and PI88788, form the basis for cultivars with SCN resistance,” Quintanilla says. “We want to learn the long-term effects of using these two varieties.”

Through a research project supported by the Michigan Soybean Promotion Committee, the nematologist is answering the question of what would happen if farmers planted one of these varieties every soybean-growing season. Quintanilla wanted to learn how this would affect nematode numbers as well as yield.

“The Peking variety is a good tool to combat SCN, especially in the first year,” Quintanilla says. “In the first year of the study, there was a significant yield increase and a nematode reduction, compared to the PI88788 variety.”

Quintanilla’s first-year results aligned with Iowa State University plant pathology professor Greg Tylka’s SCN research, which also showed higher yields and lower nematode counts with Peking in the first year. But after that, things change. 

Yields begin to decrease with the number of times that Peking was grown in the fields. Quintanilla found if Peking is planted two years in a row or more, soybean yield goes down. The best results she and her research team found in the trial was a rotation of the two varieties. The rotation between PI87788 and Peking maintained higher yields and the greatest reduction in nematodes.

“With this rotation, we had high yields and low nematode numbers every time,” she says. “In other plots with different scenarios, we saw the opposite: low yields with high nematode numbers.” 

Most farmers rotate crops each growing season, which Quintanilla considered in the study, but the addition of a corn crop didn’t change the results for SCN or soybean yield outcomes. Her research showed that using Peking alternated with a corn crop still produced low yields. 

To reduce SCN, she offered an example of a crop rotation to consider:

• Year 1: PI88788 
• Year 2: corn
• Year 3: Peking
• Year 4: PI88788
• Year 5: corn

Quintanilla suggested to steer clear of the rotation of Peking–corn–Peking–corn. 

“By our fourth year of study we found that the Peking planted back-to-back had yields lower than the control plot of SCN susceptible soybeans,” Quintanilla remarks. “Something is happening, and the resistance is breaking down when Peking varieties are grown year after year.”

Peking is a great tool to use with PI88788, Quintanilla says, but Peking does not seem to stand up to time. She is not recommending farmers to replace PI88788 with Peking, but to use Peking with moderation in a crop rotation. 

Manure application study

Quintanilla is also studying the use of manure to reduce SCN presence. She is conducting a field trial to reduce SCN using chicken manure. She applied the manure at 2 lbs./acre in corn the year prior to planting soybeans.  The corn crop gets the fertilizer benefits, and the soybeans get the SCN reduction benefits the following year.

In the first year of the project, there was a nematode reduction significant enough to continue to pursue the research. She discovered an increase in juvenile nematodes but saw a decrease of eggs and cysts. 

“It seems like the cysts are hatching and there’s a greater number of juveniles in the soil,” Quintanilla says. “So, when the SCN hatches into corn, they die because there’s no soybean to feed on.”

She said this study is focused on finding the best manure application rate to have an impact on SCN but not be over-applied, and to be mindful of environmental and soil health ramifications. 

“With this low rate, you can have an impact, but it is not enough to use as the only method of control,” she says. “This could be another tool in the arsenal for growers who are already using manure as fertilizer.”

Quintanilla says the best way to control SCN is not to get it. She suggests washing machinery between entering fields, especially if the machinery is borrowed. For best results, she also suggests to soil-sample often in addition to using SCN-resistant varieties and alternating them each soybean growing year.

Published: Aug 9, 2021