The most cost-efficient means of controlling nematodes in cotton may be to hit them only in parts of the field where they’re inflicting economic damage — which provides a great opportunity for growers to employ precision agriculture techniques like electrical soil conductivity mapping, zone sampling and site specific applications.
University of Arkansas Extension Plant Pathologist Scott Monfort says nematode control lends itself to precision agriculture so well because of the relationship between nematode damage and soil type, the lack of nematode-resistant cotton varieties, soil variability in the Mid-South and the significant cost of making broadcast applications of a nematicide to control the pests.
Two nematode species are responsible for damage in Arkansas cotton fields, reniform and root knot, with the latter being the most predominant.
According to Monfort, about 88 percent of the samples received by the University of Arkansas for nematode testing come from cotton fields. Of that percentage, 33 percent have some level of root knot nematode infestation. Reniform nematode populations fluctuate anywhere from 4 percent to 12 percent of the samples.
“Reniform is starting to surface more and more in the state,” Monfort says. “In most of the places where we see reniform nematode, it is more uniform in the field. But that’s not always the case — we do see some soil textural changes impacting reniform nematode populations, especially in sandier soils.”
Conventional sampling methods, where growers may take only two soil samples from a 180-acre field, may not accurately reflect nematode numbers in a field. The result, Monfort says, is that, “We’re probably underestimating the nematode populations out there — it’s a far greater problem that we think.”
In the last few years, researchers at the University of Arkansas have made significant strides in site specific nematode control with the help of a Veris EC meter, or soil electrical conductivity mapping cart. It has helped them to map soil types and develop a large-field understanding of the unique relationship between nematode populations, sand content in soil, and yield loss.
For example, research indicates that a soil with 45 percent sand can yield 1.5 bales of cotton even in the presence of a large number of nematodes, almost 2,000 per pint of soil. But, as you increase the percent sand from 65 percent, the plant can’t take on as many nematodes and maintain that yield potential.
“With root knot nematode, once you get greater than 75 percent sand, there are a lot of other factors causing stress on the plant. When the plant is under stress, it doesn’t take as many nematodes to cause problems. This tells us we need to work on developing sliding thresholds if we continue to rely on using soil texture to determine soil management zones.”
Monfort says it’s important to not use Veris-acquired information to treat only the sandy areas — assuming that’s where the nematodes are. “You have to know what is in the field. The Veris isn’t going to tell you where the nematode problem is; it’s only going to tell you where the variability of the soil is.”
Researchers are making progress in making site specific applications pay for producers, albeit slowly. Recent studies indicate that a blanket application of the nematicide Telone at a 3-gallon rate resulted in a higher yield than plots where a site specific application of Telone was made. “This shows we still have room for improvement,” Monfort says.
On the other hand, yield for the site specific application was 75 more pounds per acre more than the untreated check and reduced the Telone application, compared to a flat rate application, by 36 percent. That brought the Telone cost down to an estimated $26 per acre treatment.
Overall, Monfort says, there is a slight economic advantage to site specific Telone application over the flat rate application
“We’ve had years where the site specific applications out-yielded 3 gallons of Telone, but that isn’t always the case. We’re still trying to understand our thresholds, where the nematode is doing damage in the different soil types. That’s where we have room to improve, and once we nail that down a little bit, I think we’ll see yields go up.
“One thing we’ve noticed is, where we have severe nematode problems and it’s spotty, the quickest return for your money is to go to site specific control — that is, if you have the right information to base your application maps on.”
One aspect of site specific nematode control, integrating equipment and electronics, has seen significant advancement in the last few years.
“This past year, we finished the last piece of puzzle, partnering the Telone equipment with the John Deere GPS-guided systems,” Monfort says. “We can basically make site specific application work on anybody’s farm on almost any type of equipment setup.”
The impact of tillage on nematodes is also a consideration. Researchers recently conducted a study in a nematode-infested cotton field in which alternating 48-row strips were ripped and not ripped. Telone was also applied in 12-row sections within the ripped and upripped plots.
The study indicated that the untreated, unripped plots had the highest gall ratings, as did the ripped, untreated plots. But, Telone significantly reduced the amount of damage from nematodes in both ripped and unripped strips.
The highest yielding plots in the study were the ripped, treated plots, although the untreated, ripped fields did well, too.
“Just from the tillage alone, there was a 120-pound yield difference because ripping allowed the root system to penetrate farther and get away from some of the problems, like black root rot and nematodes. Where it was unripped, it didn’t allow the plant to get away from the nematodes and black root rot due to significant hardpan issues.”
Monfort says the research community’s biggest challenge in site specific applications for nematode management “is making sure that growers are aware of our research. The one area where we are limited in most is education — we need to concentrate on ways to bring consultants and producers together to work on data management and data collection.”
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