AgCenter nematologist Tristan Watson examines a research plot at the Northeast Research Station near St. Joseph. He is looking for signs that nematodes are feeding on the plants, which leads to a stunting of the plants. Photo by Craig Gautreaux

Come rain or shine or blistering heat, Tristan Watson is hard at work finding answers for questions regarding controlling nematodes.

Watson, a native of Canada, has been busy for three years adapting strategies to combat nematodes in soybean production, much like a Canadian must adapt to Louisiana summers.

To see exactly what a nematode looks like, one would need a microscope, but for many Louisiana farmers, the damage caused by these organisms can be seen in their fields quite easily.

“The reniform and Southern root-knot nematodes feed on the roots of plants. They are reducing the ability of the roots to access water and nutrients,” Watson said. “The symptoms will look a lot like nutrient deficiencies.”

These two nematodes are the most common in Louisiana agricultural fields. They often target cotton and sweet potatoes, but they will also feed on soybeans. A survey of fields found root-knot nematodes in 20% of the fields examined and reniform nematodes inhabiting more than 60% of the fields.

To farmers, the number of nematodes present can mean a big difference in their bottom line because higher numbers will lead to yield loss.

“Yield loss is going to depend on the site, obviously, and the level of nematode infestation,” Watson said. “In severe root-knot infestations, we can get up to 50% yield loss.”

Damage caused by the root-knot nematode is easier to diagnose.

“It causes galls on the root system,” Watson said. “If you think you have a problem with this nematode, go out in your field and uproot a plant, probably midseason to late season. Look for the symptoms, but don’t confuse them for nodules associated with nitrogen fixing bacteria.”

Diagnosing a reniform nematode problem is a bit more complex.

“To diagnose that one, you’re probably going to have to pull soil samples and send them to the LSU AgCenter Nematode Advisory Service,” he said. “There we can take the soil, extract the nematodes, quantify how many of the reniform nematodes you have and let you know how likely you’ll have yield loss at that population level.”

Watson has been tasked to help develop tactics for reducing nematode pressure in soybean fields, and he has seen some promise with soybean lines that have shown resistance, particularly for the reniform nematode. Much of his research is being conducted at the Northeast Research Station in St. Joseph and the Macon Ridge Research Station in Winnsboro.

Watson’s early research looked at the most common soybean varieties grown in Louisiana. All of these varieties supported reniform nematode population development. So, he looked north, not to Canada but Missouri. Some varieties developed there claimed resistance to this pest, and Watson added them to his research trials.

“These lines seemed to not support any nematode reproduction. The population levels just plummeted,” Watson said. “And we also outyielded some of the commercial lines that are currently grown here. I think we are onto something.”

Like a good scientist, Watson is replicating the study again in 2023 to see if the results hold true before making a recommendation to growers. If the results are the same, what’s next?

“Where I’d like this project to go next is commercialization,” he said. “I hope that some of our commercial seed producers, developers, see the utility of these traits and the benefit we can have for our growers and start incorporating that into newer varieties.”

The chemical nematicide Velum was recently granted approval for use in soybeans for nematodes. It has been used in cotton and sweet potato production, and it has shown good efficacy at controlling root-knot and reniform nematodes, according to Watson.

Just because a pesticide has gained approval for being applied to a new crop, it doesn’t necessarily mean it is a cure-all for that crop. Watson is examining it both for its effectiveness and any potential problems.

“We actually saw a little bit of plant toxicity in our preliminary greenhouse trials, but when we put the compound out in the real-world setting, we didn’t see that,” Watson said. “So that is quite promising.”

Watson sees two potential barriers for using Velum in soybean production. He said it is a more expensive product in comparison to other products currently used for nematode control. Another issue is application. Growers would need to make a liquid in-furrow application while the seeds are being planted, which is not something growers typically do during planting.

Tristan Watson examines soybean roots for damage. Photo by Craig Gautreaux