Perry Galloway likes to call himself a retired cotton farmer. He still grows roughly 10,000 acres of corn, soybeans, rice and a little bit of wheat.
But like most farms that have produced cotton over the past century, Galloway’s land near Augusta, Ark., is hiding a major pest beneath its surface — the southern root-knot nematode.
“The root-knot nematode is a real nemesis for me,” Galloway said. “It can be overwhelming in some fields.”
While root-knot nematodes are found throughout the South, and in almost every row crop producing county in Arkansas, some of Galloway’s fields are plagued with extremely high populations. As a comparison, the treatment threshold for southern root-knot nematode in Arkansas is 225 per pint of soil, while Galloway says soil samples collected from his fields have contained as many as 3,000 nematodes per pint of soil.
“It starts small at first,” Galloway said. “You may not even realize it’s a nematode problem. You may think it’s a fertility issue or a wet spot in the field, because they’re typically round spots that just keep getting bigger. Some of the fields where I really have problems now, may have just been one little spot five years ago. Over time those spots get bigger and bigger and worse and worse.”
“Years of rotating soybeans with wheat, and not actively managing for nematodes caught up with us,” Galloway continued. “Managing root-knot nematodes is a numbers game.”
The microscopic southern root-knot nematode enters roots of susceptible plants and establishes permanent feeding sites. As a result of the feeding, large galls or knots can form throughout the root system of the infected plant. Because root-knot nematodes interfere with normal root function, nutritional deficiency symptoms are commonly associated with nematode-infected plants.
“If you’re harvesting and have issues in the field, usually the plant will be discolored, a little lighter color, where the nematodes are. Don’t kid yourself and think it’s fertility or a wet spot or it’s not enough to matter, because eventually it’s definitely going to affect your bottom line,” Galloway said.
Travis Faske, Extension plant pathologist for the University of Arkansas System Division of Agriculture says southern root-knot nematode is the most damaging species of nematode and can actually kill susceptible plants in sandy soil types if populations are high enough. Galloway has seen this firsthand.
“I have fields where my soybeans are yielding 80-90 bu/a until we get to the nematode hotspots where the plants have just been annihilated,” Galloway said. “Those spots are yielding zero.”
While these nematode hotspots comprise less than 10% of Galloway’s total acres, the dramatic yield losses are notable. Unfortunately, there are very few management options when it comes to root-knot nematode, particularly in fields with extremely high population levels. Faske, describes it as “an old problem without many new solutions.”
“Southern root-knot nematodes were first documented in a field in Alabama in 1899, and if that field is still in production, nematodes are still in that field,” Faske said. “You live with them, you farm with them, but if you catch them early enough hopefully you can make small changes to your operation instead of drastic ones.”
“We’re adapting and trying to figure out what to do. Unfortunately, there’s no silver bullet,” Galloway said.
For growers wanting to plant soybeans or cotton, selecting resistant varieties is the first step in managing nematodes, but Galloway says in high density populations, it’s not always a cut and dry decision.
“We’re certainly conscious of it when we choose soybean varieties,” Galloway said. “It’s been my experience with my high numbers if you’re planting moderately resistant varieties, you’re wasting your time. The nematodes will walk right through that. I’ve even had complete failures on a fully resistant variety.”
Faske agrees that high population densities along with environmental stresses can make a moderately resistant variety look susceptible.
“Some varieties perform fine in a lower population, but crash when they are planted in levels like Perry’s. Also, stress in the summertime, such as lack of water, can cause increased plant stress,” Faske said. “The nematodes themselves are basically plugging up the vascular system. They’re keeping the plant from getting the water and nutrients it needs, so it crashes.”
For the past four years, Faske has tested potentially resistant soybean varieties in moderate to high density root-knot nematode populations. The results of these screenings are available online.
Faske recommends that soybean growers test soil every three to five years to determine which nematodes are present and to see if population densities have changed.
Not only are nematode control options limited, but almost every crop grown in Arkansas is a host — except for peanuts.
“Planting peanuts is the one practice where farmers can get a paycheck at the end of the season and control their nematodes,” said Faske. “Some of our cotton farmers have seen a 200 lb lint yield increase after rotating to peanuts, and that’s attributed to reducing nematode populations.”
While peanut production can be profitable, it’s not an easy fix, and can be a big initial investment if growers are purchasing their own harvesting equipment.
Galloway plans to plant peanuts for the first time in 2021. He’s contracting with another grower to plant and harvest 300 acres of peanuts on his problem fields.
“My plan is to do this for four to five years and go to a different area each year,” Galloway said.
When adding peanuts to a crop rotation, Faske cautions not to grow peanuts (or peanuts and soybeans) in back-to-back years to avoid disease build up and bridging disease pathogens between legume crops. For growers with relatively low numbers of nematodes, a common rotation is two years of cotton, one year of peanuts. Others have had success with a peanut-cotton-corn rotation.
“There are some management practices we can use coupled with some nematicide options, but most are expensive or not that great for extreme situations,” Galloway said.
Galloway has tried numerous nematicides to protect his soybean crops over the years. He’s found Telone, a pre-plant soil fumigant, to be very effective at controlling nematodes. It’s also expensive. At roughly $60 an acre, plus the cost of application equipment, he says it doesn’t always pencil out with a soybean crop. Plus, there’s the inconvenience of waiting 14 days after application before planting to protect the germ of the seed.
New this year, Galloway experimented with BIOst Nematicide 100, a biological-based broad-spectrum nematicide. Galloway says it’s also not particularly cheap, but based on one year of experience, looks like a promising control option.
“Just based on a limited one-year experience, I’m cautiously excited about BIOst,” Galloway said. “I hope it’s as good as it appears to be.”
Faske has seen good and poor results with BIOst in his research trials, which is similar to most of the other seed-applied nematicides, citing inconsistencies in yield response from year to year. These trials are conducted in moderate to high nematode densities, and seed applied nematicides are not as effective at severe nematode thresholds as fumigants.
“Someone explained it one time as you need a band-aid or a tourniquet,” Faske said. “When you have those high numbers, you need a tourniquet, you need a fumigant like Telone. If you have low populations, you can get by with a band-aid, which would be the seed applied nematicides.”
Don’t ignore it
While it’s easy to turn a blind eye to an invisible pest, Galloway’s advice is don’t ignore it.
“You may not want to spend the money for another seed treatment or sacrifice a little yield by planting a resistant variety, but don’t ignore it. It’s not hard to ignore at harvest, because you know you have a problem, but when it’s planting time, everyone wants to ignore it. It’s like it’s out of sight out of mind.”