Once the seed hits the furrow and it’s covered with soil, the battle has begun. It starts with nematodes. Once the furrow is closed, it’s largely a matter of how well the seed survives the first six weeks.
Making effective and timely decisions is everything, according to Bob Kemerait, Ph.D., Professor and Extension Specialist, Department of Plant Pathology, University of Georgia.
Before the Furrow Closes
“It is critical to ensure that you have the right seed or the right nematicide in the furrow before the furrow is closed,” Kemerait says. “Once the furrow is closed, nearly all of your nematode management options are over. Growers MUST NOT miss this opportunity to make the best decision. Missing the chance to fight nematodes at planting means watching from the sidelines for the rest of the season as the cotton crop takes a beating. Also, nematodes may affect not only the crop, but also the impact of every other input invested into growing the crop.”
When it comes to nematodes, it’s an issue that will most likely persist not only for the current season, but for years, according to Adrienne Gorny, Ph.D., Assistant Professor, Nematode Epidemiology and Management, University of North Carolina State University.
“Unfortunately, nematodes and other soil borne diseases tend to be ‘long term’ problems,” Gorny says “Once nematodes are established in the field, they have the potential to cause economic problems year after year.”
“Nematode sampling is great information to have,” says John Mueller, Ph.D., Professor of Plant Pathology, Edisto Research and Education Center. “But between the logistics and cost of running samples I can understand why growers are sometimes reluctant.
Shifting Nematode Populations and Species
Across much of the Cotton Belt, the most common nematode species of concern have traditionally been reniform and root-knot. Even that balance of concern tends to shift over time.
“In Louisiana, we have been seeing a gradual displacement of Southern root-knot nematode (Meloidogyne incognita) with the reniform nematode (Rotylenchulus reniformis),” says Tristan Watson, Ph.D., Assistant Professor, Department of Plant Pathology and Crop Physiology, LSU AgCenter.
“In a recent survey of 118 Louisiana soybean fields conducted in 2020, Southern root-knot nematode was recovered from 19.5 percent of fields, and reniform nematode from 61.9 percent,” he says.
“When present in a field, population densities of either nematode species were often well above the established damage threshold for soybean and cotton in Louisiana. Why the reniform nematode is becoming more prevalent in Louisiana production fields is unknown. However, a faster life cycle and enhanced overwintering capacity relative to Southern root-knot nematode may be contributing factors.”
In some areas, new species are becoming an increasing issue for growers and impacting multiple crops.
“Soybean cyst nematode (Heterodera glycines) continues to spread in North Carolina and other areas of the US,” Gorny says. “In North Carolina, this species has been reported in two new counties since 2017. Another nematode – Meloidogyne enterolobii – commonly referred to as the guava root-knot nematode – is an introduced species of root-knot nematode that is highly aggressive on numerous crops.
“Unfortunately, we are seeing M. enterolobii expand in distribution in North Carolina. It has currently been confirmed in 13 counties, mainly in the central and eastern part of the state.”
Columbia Lance Emerging
In many areas of South Carolina and some parts of North Carolina and Georgia, Columbia lance nematode has emerged as a more serious concern over the past few years causing increasingly severe yield losses in corn, cotton and soybean, according to Mueller.
“Its distribution is limited to the coarse textured sandy soils typical of the Coastal Plain in South Carolina,” Mueller says. “These soils are typically where we also see the most damage from Southern root-knot nematode. While we may see reductions in Southern root-knot populations with resistant varieties, we may see that offset by an increase in Columbia lance nematode.”
Columbia lance nematode has also been detected in Alabama, Florida, and Louisiana. Nematologists in other areas of the Cotton Belt are certainly on the lookout for it as well.
Dragging the Problem Through the Dirt
More problematic than a nematode moving a relative short distance from plant to plant, is the ability of that nematode to hitch a ride on equipment being moved from field to field. Nematologists stress the importance of cleaning equipment on a regular basis, particularly when moving from a known nematode-infested field to another field. Consultants echo the same concern.
“I think it’s a very good practice to routinely clean equipment when moving from field to field,” says Jerry Adams, JLA Consulting Service, Bishopville, SC.
“If you’re moving equipment through nematode infested dirt, you’re picking up nematodes and moving them wherever you go next. In reality, very few growers clean their equipment when they’re moving to another field. It’s a hassle, but it should be considered a lot more than it is. If you’ve got a nematode infestation in one field, why do you want to transport the problem across the road?”
Chemical Management Options
Although cultural practices such as rotation to non-host crops and planting nematode resistant varieties (if available) can help curb injury from nematodes, chemical control is often needed to suppress nematode populations to an acceptable level.
There are numerous options such as seed treatments, resistant or tolerant varieties, liquid in-furrow nematicides and fumigants. Fumigants are arguably the most effective method of controlling any nematode issue that might exist – at a very high cost.
A little over 50 years ago, aldicarb, originally marketed as Temik, was commercially introduced in 1970 for control of nematodes and early season foliar pests. Today it’s marketed as AgLogic aldicarb. Essentially the same product, it’s still being evaluated by almost every nematologist in current day research trials.
“I can’t remember a year when aldicarb wasn’t included in one of my nematicide trials,” says Kathy Lawrence, Ph.D., Professor, Entomology and Plant Pathology, Auburn University. “It’s always been a consistent standard for comparison because its performance is so predictable.”
That’s not an isolated opinion.
“In terms of non-fumigant nematicides, it is the gold standard for nematode control across a wide range of species,” says Travis Faske, Ph.D., professor and extension plant pathologist, University of Arkansas, Lonoke Extension Center. “After decades of data, it’s hard to argue with its performance.”
Built-in Resistance
“For both cotton and soybean, resistant varieties are our best lines of defense for southern n root-knot nematode,” Mueller says. “We have resistance now to reniform in high yielding cotton varieties, so that is our starting point to control it. There is resistance to reniform nematode in a few soybean varieties that are suited to South Carolina, but sometimes they are hard to find.
“The niche for aldicarb in both crops is in fields where you have Columbia lance, lesion and/or stubby root nematodes and want to grow cotton or soybeans,” he continues. “We currently have no resistance to any of those three species in cotton or soybean. Peanut is the only rotation crop that will reduce levels of Columbia lance nematodes. But even rotation with peanuts will allow the buildup of lesion nematode populations.”
In most situations, fumigation is simply cost-prohibitive, cumbersome, and time-consuming.
“You’re simply not going to find a lot of growers who are going to spend the money to fumigate for nematodes,” Faske says. “It usually doesn’t pencil out.
“In most cases, the next most effective option is aldicarb,” he says. “Of all the non-fumigant alternatives, AgLogic aldicarb is the most consistent product available. That’s why we include it in research trials every year. It’s a benchmark for which all others are measured.”
Many nematologists across the Cotton Belt agree with this assessment.
“AgLogic (aldicarb) is an important tool – among our most effective nematicides – for protecting yield in our peanut, cotton, and soybean crops,” Kemerait says. “Short of using a resistant variety or fumigating with Telone II, AgLogic aldicarb is as good or better, than any other options our growers have to battle nematodes.”
That’s 50-something years of data.