Better monitoring and education may help control plant-parasitic nematodes

UNIVERSITY PARK, Pa. — Microscopic worms! Nematodes are tiny roundworms that can have big effects on our lives, including infesting plants and causing more than $170 billion in annual losses for agriculture globally. But a new literature review by Penn State researchers synthesizes findings from previous studies, suggesting that implementing advanced biosecurity measures could reduce infestation rates in crops by up to 70%.

Biosecurity — management practices put in place to prevent the spread of diseases in crops, livestock, natural environments, and people — includes controlling the spread of plant-parasitic nematodes in agriculture and the food supply chain. The authors said combining emerging monitoring technologies with traditional prevention methods and stakeholder education could substantially reduce crop yield losses and thus bolster food security.

The review — which assessed the biosecurity risks, management difficulties, and potential control methods of plant-parasitic nematodes — was published in Frontiers of Plant Science.

First author Camelia Kantor, associate research professor and associate director of strategic initiatives at the Huck Institutes of the Life Sciences, noted that this review highlighted important strategies for regular monitoring of this small but mighty agricultural pest.

"Plant-parasitic nematodes pose a direct threat to crop yields and quality," she said. "Our review paper introduces a new interdisciplinary framework for synthesizing plant parasitic nematode-related biosecurity risks. The novelty also lies in the fact that we are fostering dialogue and collaborations between nematologists and geospatial scientists to tackle agricultural challenges. Advancing modern detection and management techniques is essential to ensuring the integrity of the food supply chain and protecting crop health — efforts that demand cross-disciplinary innovation."

Most plant-parasitic nematodes live underground and are considered one of the most important soil-dwelling organisms because of their abundance, ability to adapt to almost any environment, and their effects on the fitness of organisms growing around them. Many people have never seen a nematode, the researchers said, but they might have seen the damage caused by them.

Plant-parasitic nematodes can stunt plant growth and spread plant diseases, Camelia Kantor said. Unfortunately, it can be hard to diagnose nematode damage because the symptoms of nematode feeding resemble those of nutrient deficiencies, unfavorable weather conditions, and other stressors to the plant.

Still, not all nematodes are harmful. There are many beneficial species of nematodes, such as entomopathogenic nematodes, which parasitize harmful insect pests. The main distinguishing feature between plant-parasitic nematodes and other nematodes is the plant-parasitic nematode’s stylet, a sharp mouthpart used to puncture plant roots, said Mihail Kantor, assistant professor of nematology in the College of Agricultural Sciences.

"They use the stylet to puncture the plant roots, the stem, or the leaf of the host plant, and that enables them to go inside and feed on the nutrients of the plant," he said.

Most plant-parasitic nematodes live underground and are considered some of the most important soil-dwelling organisms because of their abundance, ability to adapt to almost any environment and their effects on the fitness of organisms growing around them. Many people have never seen a nematode, the researchers said, but they might have seen the damage caused by them.

"Until recently, while a lot of farmers would know about other diseases and insect pests that were visible to the eye, they would not know about nematodes," Mihail Kantor said. "Now, through the efforts of Penn State researchers, including the Nematode Diagnostic Lab at Penn State, there's a growing number of farmers who are starting to learn more about how nematodes are impacting their crops."

Nematodes are ubiquitous, spread easily, and are particularly resistant to current management practices, the researchers pointed out. The pests can spread when contaminated soil is transported to other fields, like when it clings to fresh produce or is tracked from muddy boots or dirty farm equipment. They can survive for a few weeks in films on water and infect new areas through water runoff, rivers connected to irrigation systems, ponds, lakes, and dams. Seeds, bulbs, and plant cuttings can also harbor nematodes and be transported large distances.

Many plant-parasitic nematodes also can undergo anhydrobiosis — the ability to live for long periods of time without water — which makes them very resilient and almost impossible to eliminate. In addition to seeking solutions for eradication, the researchers said that efforts should be focused on the detection and prevention of spread.

But while nematodes are widespread, the expertise needed to identify them is not. There is a need for more nematode experts, Camelia Kantor said, and emerging biosecurity advancements potentially could help mitigate the lack of nematologists.

"Currently, it’s a narrow area of expertise, and only a few people know how to identify plant-parasitic nematodes," she said. "But increasingly, there are more ways of surveying and identifying. Recent technological advancements in imaging can help growers narrow down the specific areas where they should be collecting, sampling, and observing."

She explained that with advancements in geospatial surveillance technology, recurring monitoring can pinpoint areas at risk for nematodes, enabling field investigations to confirm their presence.

"Tools and technologies such as unmanned aircraft systems, combined with spectral imaging, offer rapid, nondestructive methods to capture multispectral data on crop stress," she said. "While in many cases we don’t yet have enough data to identify specific areas affected by nematodes, we have enough to say, ‘Oh, this area of the field has certain characteristics that suggest potential infestations.’ These tools are transforming the field, allowing us to concentrate efforts on the most vulnerable areas, optimizing detection and management strategies."

Beyond knowing if a field has nematodes or not, identifying the type of plant-parasitic nematode is crucial for control efforts.

"The root-knot nematodes are probably the most known," Mihail Kantor said, "and the number one issue worldwide as far as the damage that they cause. But that doesn't mean that the other ones are not important. The most damaging nematode depends on the crop that you have."

And once farmers know what they have, he said, they can take action and better plan which crops to grow.

"A lot of farmers do cover crops and crop rotations, and by knowing what type of nematodes you have and what plants they prefer, you can avoid planting cover crops that are known good hosts for nematodes," he said. "For example, I think the most commonly used group of cover crops to suppress nematodes are the brassicas. In some southern states such as South Carolina and Florida, some white clover varieties with resistance to nematodes are also used successfully to control them."

Other traditional methods used to prevent nematodes include regular cleaning of farm equipment, using certified nematode-free planting material, managing soil moisture and weeds, and applying nematicides when necessary. Sanitation is particularly important to prevent the spread of nematodes through packing materials, and quarantines are sometimes necessary to prevent regional/global spread of nematodes.

Mihail Kantor further emphasized the importance of extension education efforts to inform growers about nematodes.

"The best way to deal with nematodes is, first, to know what you have and what numbers you have," he said. "To find that, growers should collect soil samples and send them to specialized diagnostic labs. For example, in Pennsylvania, you could send samples to the Nematode Diagnostic Lab at Penn State."

Jonathan D. Eisenback, from the School of Plant and Environmental Science at Virginia Tech, was a co-author on the study.

The U.S. Department of Agriculture's National Institute of Food and Agriculture helped support this work.

Writer/contact: Alison Jennings, ahj5145@psu.edu, Graduate student in entomology