Research Highlights

New Resistant Varieties Prove Challenging for Nematode Management in Soybeans

Highlights:

• Reniform nematode can be found in more than 50% of Louisiana soybean fields, according to researcher estimates, costing more than 500,000 bushels in yield.
• New genetic regions in the soybean genome have been associated with reniform nematode resistance and shared for use in developing new resistant varieties.  
• Combining nematicides and resistant soybean varieties could help protect soybeans from southern root-knot nematode damage and reduce nematode populations for future seasons. 

---

Reprinted with permission from the 2026 Louisiana Soybean & Grain Research & Promotion Report, August 7, 2026

By V. Todd Miller, LSU AgCenter

Nematodes are microscopic roundworms that feed on plant roots, which reduces yields and poses a financial burden on producers. Tristan Watson, a nematologist and associate professor in the Louisiana State University AgCenter Department of Plant Pathology and Crop Physiology, has been working tirelessly to combat the pest, with ongoing support from the Louisiana Soybean and Grain Research and Promotion Board.

Watson has been evaluating soybean varieties for resistance to the reniform nematode, which he estimates is in more than 50% of Louisiana soybean fields. He says he hopes to make recommendations to growers soon.

“We’ve already demonstrated that deploying experimental soybean varieties with host resistance can reduce reniform nematode populations and improve yield in our prior studies,” he said. “Now that reniform nematode-resistant soybean varieties are beginning to become commercially available to growers, we are shifting our focus to evaluating these new varieties for suitability as a nematode management tool in Louisiana.”

According to Watson, in 2025, the reniform nematode was responsible for a 1.25% reduction in Louisiana soybean yields. This amounted to a loss of more than 500,000 bushels and $5.8 million.

The reniform nematode is known to reduce the size of soybean root systems but does not cause obvious root deformation like other nematode species. Thus, it can be challenging to diagnose infestations, Watson said.

One way to spot a reniform nematode infestation is high variability in plant height, which gives rows a wavelike appearance. While most other nematodes have a patchier distribution, the reniform variety tends to be more broadly dispersed in infested fields.

“Although the overall damage on an individual plant is only moderate under severe infestations and rarely causes plant death, the cumulative impact of reniform nematode feeding across an entire field can cause serious yield losses for Louisiana growers,” Watson said.

Watson said that, in a related project, doctoral student Lucy Kiarie has identified new genetic regions in the soybean genome associated with reniform nematode resistance which can be utilized by soybean breeding programs around the country to develop new resistant varieties.

Another major threat to Louisiana soybean production, according to Watson, is the southern root-knot nematode.

Watson believes a multifaceted approach is crucial to managing this highly damaging nematode. He’s studying new nematicide chemistries and application methods to help protect young soybean roots from nematode feeding. With help from AgCenter soybean specialist David Moseley, he has set up trials across Louisiana to evaluate new resistant varieties.

“Although numerous soybean varieties are advertised as root-knot nematode resistant, most of these varieties only help to protect yield in infested fields and do not actively reduce nematode numbers,” Watson said. “This is a problem because growers then have to plant into a field with a high potential for root-knot nematode problems the next growing season.”

The southern root-knot nematode is present in about 15% of soybean fields in the state, Watson said. It causes root galling, severely stunts plants and can eventually lead to plant death.

The southern root-knot nematode diminished Louisiana soybean yields by 2%, or approximately 875,000 bushels, in 2025. That translates to an economic loss of about $9.3 million.

Iris Aguilar, a doctoral student, is playing a key role in this project. She is evaluating which combination of resistant soybean varieties and nematicide chemistries provide the best protection from nematode damage.

Additional Resources

New Management Guides Help Soybean Farmers Combat Rising Nematode Threats – SRIN article

Understanding Nematode Populations is Key to Selecting Resistant Varieties – SRIN article

Southern Root-Knot Nematode Shifting with Soybean Management – SRIN article

Searching for Southern Root-Knot Nematode Resistance – SRIN article

The SCN Coalition website

Meet the Researcher: Tristan Watson University profile

The Soybean Research & Information Network (SRIN) is funded by the Soy Checkoff and the North Central Soybean Research Program. For more information about soybean research, visit the National Soybean Checkoff Research Database and the LSU AgCenter Soybean and Grain Promotion Board Reports.

Published: Aug 31, 2026