Research Highlights

Research Highlights
Exploring Management Practices to Reduce SCN Numbers

Soybean leaf infected with SDS. Photo: Daren Mueller, Crop Protection Network

By Carol Brown

For fields that have soybean cyst nematodes in the soil, which are most of them, farmers have two weapons available to fight back — planting SCN-resistant soybeans and using management practices. Researchers continue to refine and improve soybean genetics as well as management strategies to reduce SCN numbers in the field. 

Marisol Quintanilla, an assistant professor and nematologist at Michigan State University, has been looking at different ways to manage SCN for some time. She is currently exploring management strategies that will help drive SCN numbers down through a project supported by the Michigan Soybean Committee. 

“We are looking at several options including using soybeans as a trap crop,” says Quintanilla. “In fields with high SCN infestation, we are testing several different susceptible soybean varieties — ones that we know nematodes reproduce in — and allowing the eggs to hatch. Then we terminate the soybeans before the nematodes can complete reproduction. We’re making the nematodes enter the plant and then we kill the plant to stop their development.”

She calls this a nematode suicide mission. Quintanilla terminated the soybeans between four and six weeks after planting, before the nematodes can develop cysts, thus reducing their numbers in the soil. She suggests doing this on fields that are rotating to a non-soybean crop. After soybean termination, producers can plant crops that don’t host SCN, such as corn or wheat. Farmers use cover crops all the time, she says, and they should think of this practice as similar to a cover crop, but with the objective of reducing nematode numbers.

Photos A and B: Greenhouse evaluation of SCN hosts as trap crops with different sources of resistance in the soybeans (susceptible, trap soybean [PI46754], PI88788 and Peking). Photo C: Nematode inoculation and termination of trap crops. Photos: Razieh Yazdani

Quintanilla’s post-doctoral researcher, Razieh Yazdani Fazlabadi, cautions those who do this to be aware of timing.

“If a farmer uses soybean as a trap crop before the main crop, it is important to terminate it before six weeks. Beyond this time, the nematode could produce the cyst and the situation could become worse,” Yazdani comments. “Given that corn is typically planted in mid-May, trap crops should be sown at the end of March or beginning of April and terminated the first week of May prior to planting corn.”

There is an economic threshold for SCN, Yazdani says, which is four cysts per 100 CCs of soil. If there are more than four, farmers should use management techniques such as crop rotation with non-hosts, rotating SCN-resistant cultivars and incorporating compost in their fields to reduce SCN numbers.

This is why soil testing is so important. Quintanilla recommends The SCN Coalition as an excellent resource. The SCN Coalition asks farmers to “take the test,” to learn the levels of SCN in their soil. Farmers need to know the SCN numbers in each field to employ the appropriate management practices beyond using the two sources of resistance — PI88788 and Peking soybean cultivars. 

“This technique of planting a trap crop may make the most sense if nematode numbers are very high,” she says. “If farmers have stored seed or if soybean prices are good, they could use these for the trap crop to keep costs lower. We will be analyzing the economics after the trials are completed.”

Compost and Manures Also Effective

Quintanilla is conducting another study that compares how much different compost and manure mixtures reduce SCN numbers in the soil. The initial study that inspired this work looked at different manures’ impact on root lesion nematode, which significantly reduced in number when using a poultry manure or a compost blend. Because of this success, they are now testing this approach for SCN reduction.

These photos illustrate the effects of compost applications on SCN density: (A) egg hatching experiment in the laboratory; (B) measuring the effects of 10 different composts/manures on SCN population in the greenhouse; (C) selected compost and manures evaluated in microplots and (D) on the farm. Photos: Razieh Yazdani

“We’ve done some initial field trials and they have shown some reduction of nematodes,” explains Quintanilla. “It’s been between 5% and 10% reduction, and in several parts of our trials, the manure worked better than nematicides. But there is a limit to the amount of manure that can be applied to a field.”

In the lab, the team tested more than 10 different composts and manure blends for SCN reduction. The best performers were poultry manure and a “layer ash blend,” a product from a Michigan composting company consisting of poultry litter, wood ash and a compost blend. 

“The use of manures or compost is one more tool in the arsenal for controlling soybean cyst nematode,” Quintanilla says. “And compost has additional benefits such as providing nutrients, organic matter and microorganisms to the soil and helping to improve soil structure. Reducing nematodes is an extra benefit.”

Other Resources

Soybean Cyst Nematode Resistant Cultivar Rotation System Impacts Nematode Population Density, Virulence, and Yield – academic paper

The SCN Coalition website

Marisol Quintanilla profile

Published: Aug 21, 2023

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.