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Sampling key to nematode management

Part 3: Sampling is crucial for detecting nematode issues. Specialists from Texas, Arkansas, and Georgia weigh in on sampling best practices.

Ron Smith

May 1, 2023

7 Min Read
blooming cotton sunsetThe best time to sample for nematodes in Texas cotton fields is during the season, whereas in Arkansas and Georgia, sampling is best if done following harvest.Shelley E. Huguley

Nematode infestations are not as obvious as armyworms, thrips, or fleahoppers, but the damage they cause to numerous crops can be devastating. Farm Press called on Extension and Research pathologists From Texas to Georgia to ascertain the damage nematodes can cause, the symptoms to look for in-season, sampling recommendations, and management options. Also, new research seeks to find more varieties resistant to nematode damage.The first and most crucial part of managing nematode infection is identifying the problem, including determining level of pressure and specific species present.Timing and collection of representative samples are critical to identifying infection levels and creating a viable management plan.“Sampling should wait until at least 60 days after planting,” Terry Wheeler, Texas A&M AgriLife Research Pathologist, Lubbock, said. “Soil sampling for a nematode analysis is fine from 60 days to the end of the season, as long as there is good soil moisture.”She said soil tends to dry out in the fall, so sampling during the growing season “is usually better.”“Taking soil samples is the only way to determine the population density of root-knot or reniform nematode,” said Travis Faske, University of Arkansas Division of Agriculture, Lonoke.Related:Unmanaged nematode damage can exceed 50%He added that other nematodes, including lesion nematode or lance nematode, could be a problem in some states. “Lance is generally not a problem here.”He said the best time to sample in his area is just after harvest.

Sampling is crucial

“Sampling is the only way to detect problems of nematodes other than root-knot nematodes, the only one if you were scouting you could see stunted plants showing nutrition deficiencies in mid-season and could dig up and see galling.“That’s where I come in, sampling and getting farmers to sample. I’ve talked with some who say they have sampled. I ask, how long ago? ‘Well, about 15, 20 years ago’ they say. A lot of things change within their production system in that time.”“Fall is the best time,” said University of Georgia Extension Plant Pathologist Bob Kemerait, Tifton.But Kemerait said some Georgia farmers were sampling this winter. “We were seeing a number of samples come back positive for high levels of nematodes, which is unusual for samples collected during cooler winter months,” he said.He attributes those high populations to several La Niña winters, winters that are warmer than average and that allow nematodes to continue to feed.And during the winter of 2022-2023 they had a buffet. “In warmer winters, some cover crops or winter wheat could be a host,” he said. “Some common winter weeds like henbit and chickweed also might be a host in a warm winter. In a winter like we’ve had this year, nematodes never really went to bed and may want to go out and get themselves a snack.”Related:Resistant varieties, rotation suppress reniform nematodesHe said plants typically not a good host in colder winters could become fair hosts in warmer winters.Does it make sense to sample in the winter?“That’s a great question,” Kemerait said. “I would say under most circumstances no. It’s too late. But we’ve had growers across Georgia who, against my better judgment initially, took samples. They wanted to know what was in their fields. Surprisingly, we’ve found some very high levels of nematodes.”He cited two reasons to avoid taking samples during winter months. “The first is if you come back with nothing in the sample, you don’t know if that’s because there’s nothing there or because you sampled in the winter when nematode populations are suppressed. Also, our threshold levels are based upon fall counts, not spring. That makes interpretation of winter numbers a bit difficult.“On the other hand, because it’s been so warm this winter, we find successful growers who have nematode pressures at elevated levels, which we normally wouldn’t see this time of year.”Kemerait said some growers are making good decisions based on what they find in late nematode samples.“Still, I wish they had sampled in the fall.”Related:Nematode symptoms may resemble nutrient deficiencyHe added that if growers get samples with high numbers, they can make management decisions. “But if they don’t get low numbers back, they can’t know for sure if they have nothing or the timing is off. I prefer that growers sample in the fall, just after harvest, before soils get cold.”

Population changes

Faske said producers should consider that nematode population density could change over time and sometimes in spite of resistant varieties.He said producers may say, “’I don’t have a nematode problem,’ referring to root-knot but don’t think about reniform. Without a soil sample they don’t know.”Faske explained that nematode samples can be predictive or diagnostic.“If growers see a problem, stunted plants, for instance, they take a diagnostic sample to determine why those plants are stunted. They would take a sample in sick-looking plants, not the dead plants. Nematode populations will be low in dead plants.”He recommended comparing the sample area to a lush and green area in cotton, soybeans, or peanuts. “Send those two samples off and compare nematode numbers to determine if the symptom you’re seeing is related to nematode density.”He said producers take predictive samples in the fall.“Then they should ask if they can predict damage based on nematode density or are they at a level that would cause damage for a subsequent crop, cotton, soybeans or peanuts.”

Representative sample

He said samples should represent the field as accurately as possible.Samples do not have to be large, Faske said. “We don’t need a gallon of soil.”Wheeler recommends taking a composite soil sample (10 to 20 spots per sample) to a depth of 8 to 12 inches.  “You can be close to the surface, 6 to 8 inches, nearer to midseason, deeper as you get close to harvest. “Take the sample near the taproot. Mix the soil well in a bucket and put it in a plastic bag,” she said.  “Keep the sample from getting hot, or from freezing.  Nematodes are very sensitive to extreme temperatures.”Faske recommends producers stay with the same laboratory from year to year.“Although the process is generally the same, sometimes the way labs report findings are a little different.” He said Arkansas reports as per 100 cubic centimeters of soil; Mississippi reports as 500 cubic centimeters of soil; Missouri reports as 250 cubic centimeters of soil.

Thresholds

He said thresholds for nematode populations, unlike for insect pests, are difficult to establish.“If samples show more than 100 per 100 cubic centimeters of soil per root, that’s a serious problem going into soybeans or cotton and growers should think about a management tactic.”Faske said Arkansas commodity boards see nematode sampling as a critical tool in crop management and have “put their money where their mouth is, providing free assays to farmers. For the past few years, commodity boards have been paying for nematode assays.”All three agree, growers have to know what’s there before they can develop a management plan.

8 key tips for nematode sampling

Timing and technique are critical aspects of pulling, protecting, and transporting nematode samples.Morgan McCulloch, Texas A&M AgriLife, San Angelo, and Travis Faske, University of Arkansas, Division of Agriculture, Lonoke, offer tips to collect nematode samples.

  1. The best sampling time is relative to grower objectives. “For cotton management, we usually aim to sample after the cotton has reached maturity, McCulloch says. “This can happen prior to or soon after cotton harvest.” Moisture is important for nematode sampling as nematodes move with water in the soil profile. McCulloch recommends sampling when the soil is moist enough to hold its shape after squeezing gently.“Anytime you sample for nematodes, you’re aiming for the root zone of the targeted plant, around 12 inches deep for cotton,” McCulloch says.Samples should represent the field as accurately as possible, Faske says. “You wouldn’t want all of your samples to come from an obviousSample testing can get expensive; more samples are always better, but one comprehensive sample from multiple field points would provide an idea of what kind of nematodes are in a field. Protect samples. Recommendations call for placing samples in Ziploc bags to preserve moisture before the extraction process. Keep bagged samples out of direct sunlight. Transportation. “When we send samples to a commercial lab, we usually send them in a Styrofoam cooler in a cardboard box to keep them fresh,” McCulloch says. The sample form from the lab website should direct the lab to run a nematode assay to identify specific parasitic nematodes and relative densities. “Wherever you get samples processed, continue with that same laboratory,” Faske said. “Different labs report findings differently, although the procedure for assays is the same.”

Read more about:

Reniform NematodeNematodes

About the Author(s)
Ron Smith

Ron Smith

Editor, Farm Progress

Ron Smith has spent more than 30 years covering Sunbelt agriculture. Ron began his career in agricultural journalism as an Experiment Station and Extension editor at Clemson University, where he earned a Masters Degree in English in 1975. He serve

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Nematode symptoms may resemble nutrient deficiency

Part 2: Pathologists from Texas, Arkansas and Georgia weigh in on recognizing nematode symptoms and the importance of making a plan before a seed is ever planted.

Picture of Ron Smith

Ron Smith

April 24, 2023

4 Min Read

planting cotton

Nematode control: “You’re never going to get the value out of the crop you should have if you don’t call the right play before you close the furrow,” says University of Georgia Extension Plant Pathologist Bob Kemerait, Tifton.Shelley E. Huguley

Editor’s note: Nematode infestations are not as obvious as armyworms, thrips, or fleahoppers, but the damage they cause to numerous crops can be devastating. Farm Press called on Extension and Research pathologists From Texas to Georgia to ascertain the damage nematodes can cause, the symptoms to look for in-season, sampling recommendations, and management options. Also, new research seeks to find more varieties resistant to nematode damage.

Farmers who blame less productive areas in their fields on “sorry dirt,” spots where crops do not perform despite adequate fertility and rainfall or irrigation, should sample for nematodes.

“Sorry dirt is a term I commonly hear from farmers as an area where they plant crops, sometimes different crops over several seasons, and they just can’t get them to grow,” says University of Georgia Extension Plant Pathologist Bob Kemerait, Tifton.

“It’s that part of a field that has never looked good. They try to fertilize out of it. They try to irrigate out of it. They just can’t get it to grow. We’re saying growers should absolutely check to see if nematodes could be the source of the problem.”

Discovering symptoms of nematode infection in season is likely too late to apply effective control strategies, pathologists say, but identifying the problem does set the stage for developing plans for future crops.

Related:Unmanaged nematode damage can exceed 50%

Texas A&M AgriLife Research Pathologist Terry Wheeler, Lubbock, says in season root-knot nematode symptoms on cotton include “stunting and possibly an increase in seedling disease and fusarium wilt.

Look for galls

“Root-knot nematode causes galls to form in the roots, so looking at roots can help. You should see galling by 40 days or so after planting throughout the rest of the season.” 

“Foliar symptoms are often lacking or appear as nutrient deficiencies in cotton,” said Travis Faske, University of Arkansas Division of Agriculture, Lonoke. “Spindle-shaped galls are evident on root systems of stunted plants. Similar symptoms occur on peanuts. The reniform nematode causes some stunting but no galling on cotton. A soil sample will confirm a reniform nematode issue.”

When to check for symptoms

“Root galls are easier to identify after mid-season and closer to harvest,” Faske said. “Digging to examine roots is useful to identify a root-knot nematode issue; however, a nematode issue is best confirmed with a soil sample.”

Faske said identifying reniform infection is not as simple as pulling roots and checking for galls. “You pull up a root system in a suspected reniform field and you really don’t see a problem.”

Related:Resistant varieties, rotation suppress reniform nematodes

He said some think reniform-infected plants have “dirty roots,” but added that soil type might affect that strategy.

“Reniform can move into fields, even on equipment. We know of cases of reniform movement from one state to another on harvest equipment. That’s also probably how it got here (in Arkansas).

Reniform takes over

“Another dynamic with reniform is that if you put both root-knot and reniform in the same field and give it long enough on the right host, reniform will take over; it’s more adaptable to a lot of our soils, especially here in the Mid-South.”

Kemerait recommends growers scout in season for stunted plants, cotton and soybeans that are not thrifty, and foliar “tiger striping” (interveinal chlorosis). Those symptoms could result from fertility issues or from nematodes.

“With tiger striping or interveinal chlorosis, the leaf veins are green but the blade of the leaf between the veins is yellowing. That’s a strong indication of fertility deficiency but could also be nematodes.

https://1124c35824cf8697e86ed5995c70027d.safeframe.googlesyndication.com/safeframe/1-0-40/html/container.html

“Signs of nutrient deficiency on leaves could be signs of root damage. If the roots are damaged, everything you do for the rest of season will be compromised because roots do not perform as they should,” Kemerait said.

Related:Okla. peanut producers prep to plant, hopeful better conditions ahead

“Whether it’s seed cost, irrigation costs, insect control, or weed control, everything is compromised because those roots are never going to perform like they should. If the roots are boogered up, they are not taking in nutrients.”

ID the problem

Identifying the problem, either by scouting for symptoms in season or pulling samples late in the season through harvest, will not be enough to prevent losses for that year but will be the basis of future management.

Pre-plant activity makes a difference. Most effective management, Kemerait says, happens before the seed is covered.

“You’re never going to get the value out of the crop you should have if you don’t call the right play before you close the furrow.”

Read more about:Reniform NematodeNematodes

About the Author(s)

Ron Smith

Ron Smith

Editor, Farm Progress

Ron Smith has spent more than 30 years covering Sunbelt agriculture. Ron began his career in agricultural journalism as an Experiment Station and Extension editor at Clemson University, where he earned a Masters Degree in English in 1975. He served as associate editor for Southeast Farm Press from 1978 through 1

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All latest News, News March 2023, North America, Pests and Diseases, Production/Agronomy, Smart Farming

Nematicides know-how: Ways to help rid your potato crops of nematodes

on March 22, 2023

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By Carrie Huffman Wohleb. First published by American Vegetable Grower. Republished here with permission.

Many potato growers rely on nematicides to protect their crops. Following is information you should know about both fumigant and non-fumigant methods.

Fumigant Nematicides

Although you apply fumigant nematicides, like 1,3-dichloropropene (Telone II) and metam sodium (Vapam HL), to soil in liquid form, it vaporizes and diffuses through the soil as a gas. They are applied before planting.

Nematodes absorb fumigant nematicides through their body cavities, so ingestion isn’t necessary. They work best when nematodes are exposed to a lethal dose for as long as possible. Control failures often relate to poor dispersion or retention of the fumigant gas or failing to place the product where needed.

Here’s how to maximize dispersion and retention of fumigant nematicides.

Clear the soil of clods and compacted areas before application. Incorporate plant residues thoroughly and lay those on the soil surface flat to permit effective soil sealing. Soil temperature at the depth of application should be between 40°F and 80°F.

Generally, maintain soil moisture close to 80% of available water capacity, but recommendations vary depending on site-specific factors (soil texture, water availability, and weather — especially potential for rain).

Product labels are full of guidance on these points. Follow directions closely to enhance the effectiveness of fumigant applications.

If the fumigant does not contact nematodes, it will not control them.

Pay attention to soil moisture and temperature. The more mobile nematodes, especially stubby root nematodes, will move deep into the soil to avoid conditions that are too hot, cold, or dry.

Applying metam sodium with overhead sprinklers does not usually push the product deep enough to reach nematodes. This method works better for controlling weed seeds and fungal pathogens near the soil surface. Instead, inject fumigants using shank implements with attached spray nozzles at a depth of 14 to 16 inches to contact nematodes. Make sure you use the typically recommended higher rates for targeting nematodes.

Non-fumigant Nematicides

The most commonly used non-fumigant nematicides in potatoes are ethoprop (Mocap), oxamyl (e.g., VydateReturn), fluensulfone (Nimitz), and fluopyram (Velum Prime). These are granule or liquid products that percolate down through the soil in water. They are soil-applied, pre-plant or at planting, except for oxamyl and fluopyram, which may also be applied to the foliage in-season.

These products aren’t true nematicides because they do not kill nematodes immediately on contact. Instead, they have a “narcotic” effect on nematodes, temporarily paralyzing them, stopping feeding, and delaying egg hatch and molting.

These effects can be lethal if you maintain nematicide concentrations at high levels for an extended time, leading to death from starvation or poisoning. But they can also be reversed if exposure is short and/or at low concentrations.

The efficacy of non-fumigant nematicides largely depends on their solubility in water and persistence in the soil. Products that are highly soluble, like Vydate, Mocap, and (to a lesser extent) Nimitz, are mobile in the soil and distribute effectively to contact nematodes, but they can move out of the root zone with excess rainfall or irrigation.

Oxamyl breaks down rapidly in soil, so it doesn’t last long even when it isn’t leached. This is one reason why an in-furrow application of Vydate at planting must be followed with several foliar applications to achieve full season nematode suppression.

In fact, using a soil degree-day model can optimize the timing of in-season Vydate applications for controlling root-knot nematodes (it involves logging soil temperature at a 6- to 8-inch depth). The model estimates when juvenile nematodes will be present, which is helpful because juveniles are the most susceptible developmental stage of this endoparasite nematode to target with nematicides.

Ethoprop only persists in the soil for about 5 to 6 weeks, so Mocap is not recommended for severe nematode infestations of long season potatoes unless it is followed up with another nematicide.

Growers who opt to apply oxamyl, the most widely used of the non-fumigant nematicides, should know that use instructions differ depending on your region, the species of nematode targeted, and severity of nematode infestations. Study the Vydate or Return label carefully to comply with these important site-specific instructions.

The in-furrow application of oxamyl products is said to be optional, but growers should carefully consider the risks before they opt out of this application. Many nematode species are particularly active when potato roots and tubers are in their early growth phases. In fact, stubby root nematodes may not be effectively controlled if the first oxamyl application isn’t made before tuber initiation. In other words, more foliar applications will not make up for not applying oxamyl earlier.

Disclaimer: Application of a pesticide to a crop or site that is not on the label is a violation of pesticide law and may subject the applicator to civil penalties. It is your responsibility to ensure lawful use and obtain all necessary permits in advance of application.

Source: American Vegetable Grower. Original article here
Cover image: Globodera pallida cyst. Wikimedia Commons. Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services
Author: Carrie Huffman Wohleb is Associate Professor/Regional Specialist – Potato, Vegetable, and Seed Crops, at Washington State University.

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 Grahame Jackson

 Sydney NSW, Australia

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 2 days ago

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Bioluminescence May Shine Light on Roundworm Secrets

USDA

For media inquiries contact: Jan Suszkiw
Even though roundworms are nearly too small to be seen, they can pose major problems in corn, soybean, peanut and other crops. Collectively, these roundworms are known as plant-parasitic nematodes, and they cause $173 billion in crop losses worldwide each year.

These losses to crop yield and quality can occur even though chemical controls, resistant cultivars and other methods are available to farmers. So, a team of Agricultural Research Service (ARS) and university scientists decided to take a deeper dive into the basic biology of these nematodes and, more specifically, their genes for reproducing.

But the furtive nature of these millimeter-long pests and peculiarities of their lifecycle evaded the latest high-tech tools that the scientists had hoped to study them with.

Fortunately, they found a “work-around” in the form of electroporation. In short, the technique involves immersing nematodes in a plexiglass chamber with a buffer solution and pulsing it with small jolts of electricity. This stuns the creatures and temporarily opens pores in their bodies through which the solution’s chief “active ingredient” can enter—namely, bits of genetic material called NanoLuc luciferase mRNA.

Luciferase is an enzyme that oxidizes a compound called luciferin, producing a type of light called bioluminescence, such as that emitted by fireflies. In this instance, scientists “retooled” a luciferase coding sequence taken from a bioluminescent, deep-sea shrimp and electroporated it into the nematodes.

“Nematodes have primitive nervous systems,” explained Leslie Domier, a plant pathologist (retired) with the ARS Soybean/Maize Germplasm, Pathology, and Genetics Research unit in Urbana, Illinois. “When they were electroporated, they were immobilized for up to an hour, but then recovered and behaved normally.” Scientists then harvested the nematodes so that the contents of their cells, including luciferase, could be blended into a mixture called a “homogenate.” Next, they mixed the homogenate with a luciferin-like chemical called furamazine and presto—bioluminescence achieved!

Rather than observe this with the naked eye, the scientists used biochemical assays and sensitive light-detecting equipment to gauge the strength of the homogenate’s bioluminescence and determine how well their experiments had worked. So far, the researchers have successfully electroporated luciferase mRNA into the likes of soybean cyst nematodes (SCN) and root-knot nematodes—both costly crop pests—and Caenorhabditis elegans, a free-living species that doesn’t require a host in which to reproduce. 

According to Glen Hartman, another plant pathologist (ARS retired) on the research team, the approach opens the door to introducing other synthetic mRNAs into nematodes to reveal how they change and where, as well as when the nematode’s own genes are activated in cells.

There may be pest-control applications, as well. For example, electroporation could offer a way to rear laboratory colonies of soybean cyst nematodes that carry pieces of genetic code whose sole purpose is to skew the ratio of male- to-female offspring. In theory, releasing these lab-reared nematodes to mate with those in the wild would eventually cause a generational population crash.

“We hypothesized that if we could interfere with the sex determination in nematodes, we could reduce nematode populations below crop-damaging thresholds,” said Domier. That, in turn, could diminish the need for chemical controls or help prolong the effectiveness of elite, resistant cultivars favored by growers, among other potential benefits.

More details about the technique and its implications for nematode control were reported in the journal Molecular & Biochemical Parasitology by Domier, Hartman and co-authors Thanuja Thekke-Veetil and Kris Lambert—both with the University of Illinois—Nancy McCoppin (ARS), Reza Hajimorad (University of Tennessee) and Hyoun-Sub Lim (Chungnam National University).

The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in U.S. agricultural research results in $20 of economic impact.

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PLANT SCIENCE Nematodes hijack root development

MRS

Cyst nematodes (Heterodera rostochiensis is shown) are important crop plant pests because of the damage they cause by stimulating secondary root growth.PHOTO: NIGEL CATTLIN/SCIENCE SOURCE

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Cyst nematode parasites cause substantial damage to crop plants. These parasites invade plant roots, destroying internal root tissue structure and inducing root branching to provide additional feeding sites. Guarneri et al. found that cyst nematode infection triggers the accumulation of the plant hormone jasmonic acid and up-regulates a key transcription factor for root induction. These events lead to increased local biosynthesis of auxin that initiates de novo root formation in a similar manner to wound-associated root induction. Although infected plants maintained their overall root system size, increased secondary root growth was balanced by reduced primary root lengths. Therefore, pathogens can manipulate the dynamic responses of root systems for their own benefit.

New Phytol. 237, 807 (2023).

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Combatting soil-borne pathogens and nematodes vital for food security

   Delhi Bureau  0 Comments CIMMYT  9 min read

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08 November 2022, Mexico: The International Maize and Wheat Improvement Center (CIMMYT) coordinated the VIII International Cereal Nematode Symposium between September 26-29, in collaboration with the Turkish Ministry of Agriculture and Forestry, the General Directorate of Agricultural Research and Policies and Bolu Abant Izzet Baysal University.

As many as 828 million people struggle with hunger due to food shortages worldwide, while 345 million are facing acute food insecurity – a crisis underpinning discussions at this symposium in Turkey focused on controlling nematodes and soil-borne pathogens causing reduced wheat yields in semi-arid regions.

A major staple, healthy wheat crops are vital for food security because the grain provides about a fifth of calories and proteins in the human diet worldwide.

Seeking resources to feed a rapidly increasing world population is a key part of tackling global hunger, said Mustafa Alisarli, the rector of Turkey’s Bolu Abant Izzet Baysal University in his address to the 150 delegates attending the VIII International Cereal Nematode Symposium in the country’s province of Bolu.

Suat Kaymak, Head of the Plant Protection Department, on behalf of the director general of the General Directorate of Agricultural Research and Policies (GDAR), delivered an opening speech, emphasizing the urgent need to support the CIMMYT Soil-borne Pathogens (SBP) research. He stated that the SBP plays a crucial role in reducing the negative impact of nematodes and pathogens on wheat yield and ultimately improves food security. Therefore, the GDAR is supporting the SBP program by building a central soil-borne pathogens headquarters and a genebank in Ankara.

Discussions during the five-day conference were focused on strategies to improve resilience to the Cereal Cyst Nematodes (Heterodera spp.) and Root Lesion Nematodes (Pratylenchus spp.), which cause root-health degradation, and reduce moisture uptake needed for proper development of wheat.

Richard Smiley, a professor emeritus at Oregon State University, summarized his research on nematode diseases. He has studied nematodes and pathogenic fungi that invade wheat and barley roots in the Pacific Northwest of the United States for 40 years. “The grain yield gap – actual versus potential yield – in semiarid rainfed agriculture cannot be significantly reduced until water and nutrient uptake constraints caused by nematodes and Fusarium crown rot are overcome,” he said.

Experts also assessed patterns of global distribution, exchanging ideas on ways to boost international collaboration on research to curtail economic losses related to nematode and pathogen infestations.

A special session on soil-borne plant pathogenic fungi drew attention to the broad spectrum of diseases causing root rot, stem rot, crown rot and vascular wilts of wheat.

Soil-borne fungal and nematode parasites co-exist in the same ecological niche in cereal-crop field ecosystems, simultaneously attacking root systems and plant crowns thereby reducing the uptake of nutrients, especially under conditions of soil moisture stress.

Limited genetic and chemical control options exist to curtail the damage and spread of these soil-borne problems which is a challenge exacerbated by both synergistic and antagonistic interactions between nematodes and fungi.

Nematodes, by direct alteration of plant cells and consequent biochemical changes, can predispose wheat to invasion by soil borne pathogens. Some root rotting fungi can increase damage due to nematode parasites.

Integrated managementFor a holistic approach to addressing the challenge, the entire biotic community in the soil must be considered, said Hans Braun, former director of the Global Wheat Program at CIMMYT.

Braun presented efficient cereal breeding as a method for better soil-borne pathogen management. His insights highlighted the complexity of root-health problems across the region, throughout Central Asia, West Asia and North Africa (CWANA).

Richard A. Sikora, Professor emeritus and former Chairman of the Institute of Plant Protection at the University of Bonn, stated that the broad spectrum of nematode and pathogen species causing root-health problems in CWANA requires site-specific approaches for effective crop health management. Sikora added that no single technology will solve the complex root-health problems affecting wheat in the semi-arid regions. To solve all nematode and pathogen problems, all components of integrated management will be needed to improve wheat yields in the climate stressed semi-arid regions of CWANA.

Building on this theme, Timothy Paulitz, research plant pathologist at the United States Department of Agriculture Agricultural Research Service (USDA-ARS), presented on the relationship between soil biodiversity and wheat health and attempts to identify the bacterial and fungal drivers of wheat yield loss. Paulitz, who has researched soil-borne pathogens of wheat for more than 20 years stated that, “We need to understand how the complex soil biotic ecosystem impacts pathogens, nutrient uptake and efficiency and tolerance to abiotic stresses.”

Julie Nicol, former soil-borne pathologist at CIMMYT, who now coordinates the Germplasm Exchange (CAIGE) project between CIMMYT and the International Center for Agricultural Research in the Dry Areas (ICARDA) at the University of Sydney’s Plant Breeding Institute, pointed out the power of collaboration and interdisciplinary expertise in both breeding and plant pathology. The CAIGE project clearly demonstrates how valuable sources of multiple soil-borne pathogen resistance in high-yielding adapted wheat backgrounds have been identified by the CIMMYT Turkey program, she said. Validated by Australian pathologists, related information is stored in a database and is available for use by Australian and international breeding communities.

Economic losses

Root-rotting fungi and cereal nematodes are particularly problematic in rainfed systems where post-anthesis drought stress is common. Other disruptive diseases in the same family include dryland crown and the foot rot complex, which are caused mainly by the pathogens Fusarium culmorum and F. pseudograminearum.

The root lesion nematode Pratylenchus thornei can cause yield losses in wheat from 38 to 85 percent in Australia and from 12 to 37 percent in Mexico. In southern Australia, grain losses caused by Pratylenchus neglectus ranged from 16 to 23 percent and from 56 to 74 percent in some areas.

The cereal cyst nematodes (Heterodera spp.) with serious economic consequences for wheat include Heterodera avenae, H. filipjevi and H. latipons. Yield losses due to H. avenae range from 15 to 20 percent in Pakistan, 40 to 92 percent in Saudi Arabia, and 23 to 50 percent in Australia.

In Turkey, Heterodera filipjevi has caused up to 50 percent crop losses in the Central Anatolia Plateau and Heterodera avenae has caused up to 24 percent crop losses in the Eastern Mediterranean.

The genus Fusarium which includes more than a hundred species, is a globally recognized plant pathogenic fungal complex that causes significant damage to wheat on a global scale.

In wheat, Fusarium spp. cause crown-, foot-, and root- rot as well as head blight. Yield losses from Fusarium crown-rot have been as high as 35 percent in the Pacific Northwest of America and 25 to 58 percent in Australia, adding up losses annually of $13 million and $400 million respectively, due to reduced grain yield and quality. The true extent of damage in CWANA needs to be determined.

Abdelfattah Dababat, CIMMYT’s Turkey representative and leader of the soil-borne pathogens research team said, “There are examples internationally, where plant pathologists, plant breeders and agronomists have worked collaboratively and successfully developed control strategies to limit the impact of soil borne pathogens on wheat.” He mentioned the example of the development and widespread deployment of cereal cyst nematode resistant cereals in Australia that has led to innovative approaches and long-term control of this devastating pathogen.

Dababat, who coordinated the symposium for CIMMYT, explained that, “Through this symposium, scientists had the opportunity to present their research results and to develop collaborations to facilitate the development of on-farm strategies for control of these intractable soil borne pathogens in their countries.”

Paulitz stated further that soil-borne diseases have world-wide impacts even in higher input wheat systems of the United States. “The germplasm provided by CIMMYT and other international collaborators is critical for breeding programs in the Pacific Northwest, as these diseases cannot be managed by chemical or cultural techniques,” he added.

Road ahead

Delegates gained a greater understanding of the scale of distribution of cereal cyst nematodes and soil borne pathogens in wheat production systems throughout West Asia, North Africa, parts of Central Asia, Northern India, and China.

After more than 20 years of study, researchers have recognized the benefits of planting wheat varieties that are more resistant. This means placing major emphasis on host resistance through validation and integration of resistant sources using traditional and molecular methods by incorporating them into wheat germplasm for global wheat production systems, particularly those dependent on rainfed or supplementary irrigation systems.

Sikora stated that more has to be done to improve Integrated Pest Management (IPM), taking into consideration all tools wherever resistant is not available. Crop rotations for example have shown some promise in helping to mitigate the spread and impact of these diseases.

“In order to develop new disease-resistant products featuring resilience to changing environmental stress factors and higher nutritional values, modern biotechnology interventions have also been explored,” Alisarli said.

Brigitte Slaats and Matthias Gaberthueel, who represent Swiss agrichemicals and seeds group Syngenta, introduced TYMIRIUM® technology, a new solution for nematode and crown rot management in cereals. “Syngenta is committed to developing novel seed-applied solutions to effectively control early soil borne diseases and pests,” Slaats said.

It was widely recognized at the event that providing training for scientists from the Global North and South is critical. Turkey, Austria, China, Morocco, and India have all hosted workshops, which were effective in identifying the global status of the problem of cereal nematodes and forming networks and partnerships to continue working on these challenges.

Also Read: Agriculture and the agricultural economy is the strength of India: Union Agriculture Minister

(For Latest Agriculture News & Updates, follow Krishak Jagat on Google News)

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Saturday, 19 November 2022 15:31:49

Grahame Jackson posted a new submission ‘Effect of marigold (Tagetes erecta L.) on soil microbial communities in continuously cropped tobacco fields’

Submission

Effect of marigold (Tagetes erecta L.) on soil microbial communities in continuously cropped tobacco fields

Nature Scientific Reports

Scientific Reports volume 12, Article number: 19632 (2022) Cite this article

Abstract

Root-knot nematode disease is a catastrophic soil-borne disease in tobacco production. The regulation of natural microbial communities is considered a good disease management approach to suppress the incidence of soilborne diseases. In this study, the effects of tobacco (Nicotiana tabacum L.)-marigold (Tagetes erecta L.) rotation on the diversity and structure of soil microbial communities in continuously cropped tobacco fields were analyzed to manage this devastating pathogen. The results showed that the soil bacterial OTUs increased after marigold rotation and that the bacterial Shannon, ACE, Chao1 index, and fungal Shannon index were higher in the tobacco-marigold rotation fields than in the continuously cropped tobacco fields by 3.98%, 10.37%, 5.46%, and 3.43%, respectively. After marigold rotation, the relative abundances of Actinobacteria, Acidobacteria, and Ascomycota increased by 28.62%, 107.50%, and 57.44%, respectively, and the proportion of beneficial bacterial genera such as NocardioidesGemmatimonas, and Bradyrhizobium increased. In addition, our results also showed that rotation of marigold could effectively reduce the incidence of root-knot nematodes in the next crop of tobacco. These results indicate that marigold rotation had a positive effect on the soil microecological environment of continuously cropped tobacco fields, reducing the obstacles to continuous cropping of tobacco.

Read on: https://www.nature.com/articles/s41598-022-23517-x

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Verdure: Lance nematodes play hide-and-seek

Most lance juveniles are migratory and feed inside the root, making them difficult to uncover from soil samples and control with a contact nematicide.

November 2022 | Mike Fidanza 

Filed to: VerdureNematodes

The dreaded lance nematode is a microscopic roundworm that feeds both outside of (ectoparasitic) and inside (endoparasitic) turfgrass roots. Also known as the crown-headed lance nematode, this organism can infest creeping bentgrass and bermudagrass putting greens, which leads to a decline in turf quality and function, especially during periods of drought and heat stress. Turfgrasses aren’t alone, as plant parasitic nematodes are responsible for over $157 billion annually in crop loss globally (https://tinyurl.com/2p9c5cc2).

The botanical species name for lance is: Hoplolaimus galeatus (Cobb, 1913) Thorne, 1935. Hoplolaimus means weapon, and galeatus means helmet-shaped. But who are Cobb and Thorne? They are the “authority” or person(s) who named the species. Nathan Cobb, Ph.D., (1859-1932) is considered the “father of nematology” for his pioneering work with nematode taxonomy. Gerald Thorne, Ph.D., (1890-1975) worked under Cobb and wrote the classic “Principles of Nematology” textbook in 1961.

Derek Settle, Ph.D., studied the lance nematode as a doctoral student at Kansas State University in Manhattan, Kan. He wanted to learn more about their population densities and seasonal fluctuations in turfgrass root zones, so he monitored lance populations in a creeping bentgrass putting green. Sites and conditions (or treatments) were: four cultivars (Penncross, Crenshaw, L-93 and Providence), two mowing heights (0.125 or 0.157 inches [3.175 or 3.988 millimeters]), and two irrigation water amounts (1.2 or 2.4 inches [30.5 or 61.0 millimeters] per week.

The test site root zone was 98% sand with 2.1% organic matter and pH of 7.3 and naturally infested with lance. All treatments were arranged in a representative experimental design with three replications. Lance populations were intensively measured every month from July 2001 to October 2003, by collecting soil cores of 0.5-inch (1.3-centimeter) diameter × 2-inch (5.1-centimeter) depth and utilizing the sugar-flotation centrifuge method for nematode extraction and then microscopic identification. Lance nematodes collected were classified as juveniles or adults (male or female).

What did Settle— as a young, ambitious graduate student — find? For creeping bentgrass putting greens, lance populations tend to increase from late spring into the summer, peak about midsummer, decline in late summer, increase again by midautumn, then decline later in autumn going into the winter. Lance populations in the root zone are density-dependent, meaning they tend to aggregate or “clump” together and do not uniformly disperse throughout a sand root zone.

For creeping bentgrass putting greens, a good time to collect soil samples and monitor for lance populations is during May or June, prior to their midsummer peak. Keep in mind, those samples would only reveal lance adults, especially the females that feed on root surfaces. Because most lance juveniles are migratory and feed inside the root, they are nearly impossible to uncover from soil samples and nearly impossible to control with a contact nematicide.

Within the same putting green, sample from an area showing signs of wilt and poor roots and compare with a sample from a healthy area. This is the best way to determine any negative effects from lance and doesn’t depend on damage thresholds, because the weakest greens are most likely to suffer damage, while the healthiest greens may be tolerant of even the highest lance populations.

What about creeping bentgrass cultivars, mowing height or irrigation? Lance populations were similar in all sites and conditions, so those cultural practices tested didn’t affect lance populations. Unfortunately, lance nematodes are not effectively controlled by current nematicides. Therefore, cultural practices that promote healthy rooting and alleviate abiotic stress are recommended — for example, mitigating midday wilt stress by hand watering, using soil surfactants for root zone moisture management, raising mowing heights, rolling instead of mowing, avoiding excessive equipment wear in areas such as clean-up laps, and alleviating concentrated foot traffic by golfers via regular rotation of pin placement.

Settle is senior director of turfgrass programs at the Chicago District Golf Association (Lemont, Ill.). When he’s not chasing nematodes or tweeting nematode photos as @turfdom, he’s chasing his French bulldogs, Ralph and Leo.

Source: Settle, D.M., J.D. Fry, T.C. Todd and N.A. Tisserat. 2006. Populations dynamics of the lance nematode (Hoplolaimus galeatus) in creeping bentgrass. Plant Disease 90(1):44-50 (https://doi.org/10.1094/PD-90-0044).


Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 21-year member of GCSAA.

Filed to: VerdureNematodes

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Closer look reveals

https://s.tribalfusion.com

URBANA, Ill. – Nematodes, an abundant group of roundworms that exist in nearly every habitat, have long been used as model organisms for studying the function of neurons – the basic unit of animal nervous systems. For years, it was assumed that neuron anatomy was remarkably similar across this large and diverse group. A recent study by University of Illinois researchers turns that assumption on its head.

“It was a comparative study looking at all of these different species of nematodes, including some parasites, and seeing that there are some substantial differences in the number of neurons in the ventral cord,” says U of I nematologist Nathan Schroeder.

According to Schroeder, discovering this degree of variation across the group suggests that neuron number and anatomy may have changed numerous times during nematode evolution. This is significant because the evolution of nervous systems is notoriously difficult to study in complex higher animals. Being able to study the relatively simple nervous system in nematodes can shed light on some basic research questions in nervous system evolution.

pic This image shows a soybean cyst nematode hatching. Credit: Nathan Schroeder

“This group of animals has the simplicity that makes it easy to work with in the lab, but there are these differences across species. So, we can target that and figure out how nervous systems are evolving.”

On a more practical level, the results of this study may lead to development of new nematicides – pesticides that target plant-parasitic nematodes.

“We know from some of the old nematicides that the nervous system is a very effective target. Unfortunately, some of those nematicides were very broad spectrum and would target anything with a nervous system, including us,” Schroeder noted.

The study showed that soybean cyst nematodes, a major crop pest in Illinois, may have unique neurons that could be targeted by new nematicides to avoid harming beneficial soil organisms. More research will be required to determine whether such a product could be developed, but the study indicates that the potential may exist.

The authors are now focusing their attention on soybean cyst nematodes to identify unique neurons and to learn more about how those neurons affect the movement of the microscopic roundworms in the soil and in soybean plants.

source: University of Illinois College of Agricultural, Consumer and Environmental Sciences

January 14, 2016

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Registrations open to attend Pan-African Nematology Network workshop,
1-3 March 2023

From 1-3 March 2023, the second international PANEMA workshop will take place in Mbombela,
South Africa. This 3-day workshop, hosted by the University of Mpumalanga (in cooperation with
North West University, the Agricultural Research Council and with support from Syngenta), will bring
together trained nematologists, early-career researchers, students, agricultural extension workers,
farmers and other stakeholders from across South Africa, Africa and beyond. This event builds on the
success of the first PANEMA workshop, held in Eldoret, Kenya in February 2022, where more than
100 participants travelled from across Africa to attend the event.
Established in 2021, in the framework of the Erasmus+ project Capacity Building in Higher Education
(CBHE): Nematology Education in Sub-Sahara Africa (NEMEDUSSA), PANEMA (Pan-African
Nematology Network) aims to promote networking and academic exchange between nematologists
working in Africa. The focus of the network and workshop is on sharing good educational practices,
creating and strengthening networks between higher education institutes (HEIs) and other
stakeholders, and providing additional educational opportunities for those working in agriculture and
nematology.
The workshop aims to have a good balance between seminars and hands-on practice in the field and
lab, to enhance life-long learning and create opportunities for interactive discussions and networking
between stakeholders. It is also a platform where students and African nematologists can showcase
their projects and research. Next to nematode-related topics such as ‘Nematology and the One Earth
Approach’, this workshop will focus on training in scientific communication skills to create better
awareness about nematodes.
This workshop is open to farmers, agricultural extension workers, students, researchers,
nematologists and interested parties. Tthey are invited to register to attend this event in Mbombela,
which can also be followed free online. For the programme and registration link, please go to
https://nemedussa.ugent.be/2nd-panema-workshop-1-3-march-2023-2/ .
For more information about the NEMEDUSSA project and upcoming PANEMA events, please see
http://www.nemedussa.ugent.be. This project is funded with support from the European Commission.
Nematology Coordination Office: Erasmus+ CBHE project Nematology Education in Sub-Saharan
Africa (NEMEDUSSA)
For more information, reach out to: nemedussa@ugent.be
28/10/2022
What are nematodes?
Nematodes or roundworms cause significant damage and yield loss to a wide variety of crops, often together with
other pathogens. At the same time, nematodes can also be used as bio-control agents against insect pests and/or as
bio-control agents for environmental health and biodiversity. The NEMEDUSSA project aims to increase awareness
about nematodes and expand educational and research capacities in HEIs in Sub-Saharan Africa (SSA) in this field,
and is a joint effort by a consortium of Universities from Sub-Sahara Africa and Europe. The PANEMA workshop is the
next step in bringing nematologists together to collaborate on ways forward to address this pressing agricultural

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Guava root-knot nematode has been detected in Australia for the first time — so how concerned should farmers be?

ABC Rural

 / By Lucy Cooper and Matt Brann

Posted Mon 31 Oct 2022 at 1:47amMonday 31 Oct 2022 at 1:47am

A women sorts sweet potatoes in a packing room.
The guava root-knot nematode is one of the most damaging root- knot nematodes in the world. (ABC Wide Bay: Brad Marsellos)

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Guava root-knot nematode has been detected for the first time in Australia in the Northern Territory — leaving farmers with questions about what to do next. 

Key points:

  • Guava root-knot nematode has arrived in Australia for the first time in the Northern Territory
  • A expert from the United States is not surprised it has been found here
  • Sweet potato growers have been urged to stay vigilant and report suspected cases

The pest severely impacts sweet potatoes by damaging their roots.

It also stunts the growth of a wide range of other crops, including cotton, cucumbers, capsicums, pumpkins and zucchinis. 

The Northern Territory’s chief plant health officer said the pest had been found in four locations in the territory and the likelihood of eradication was quite low.

So how worried should farmers be and what should they do if they find it on their property?

Fumigation used in the United States

man in black shirt and hands on hips smiles at camera
Dr Johan Desaeger says fumigation is a common control method.(Supplied: University of Florida)

Johan Desaeger, an associate professor from the University of Florida, said he was not surprised to hear the pest had been found in Australia.

“Australia was the last continent, except for Antarctica, where this nematode had not been reported yet,” he said.

“It was first identified in the 1980s in China … but I believe this nematode has been around the tropics and sub-tropics across the world probably for millions of years.”

The nematode was first detected in the United States in 2004.

Mr Desaeger, who co-authored a report on the pest this year, said the nematode liked warm weather and sweet potato farmers in the United States were using fumigation to control it.

“I don’t think it’s had a big impact yet in Florida where I am, although it’s had an impact in North Carolina where it’s been impacting the sweet potato industry — but that’s more of a quarantine issue because the tubers are an ideal (host) to spread this nematode,” he said.

“My advice is to keep monitoring it, keep sampling.

“I wouldn’t go into panic mode, just be cautious and if you see root-knot on any crops, get it properly identified … the more information you have the better.”

He said he doubted it would spread to the temperate climates of Australia.

Keep an eye out for signs

The University of Southern Queensland’s Gavin Ash has been studying sweet potato pests and diseases in Australia and Papua New Guinea for the past decade.

He said root-knot nematodes were like “little tiny eels that live in the soil” and in general were one of the “highest-problem” pests for sweet potatoes.

Sweet potato in a bucket, on the ground in a paddock of rich brown soil.
Guava root-knot nematode has had a severe impact on sweet potato production in the United States. (ABC Wide Bay: Eliza Rogers)

“The problem with nematodes is they’re quite insidious — they’re small, you don’t notice them and then all of the sudden you realise you’re not getting as much yield as you used to get and your yield declines over time,” he said.

“The other really important thing with sweet potato, is that any sort of damage or blemish on the potato makes it unsaleable, because people don’t want to buy a potato with black marks or lumpy bits on them.”

He said there was a risk the guava root-knot nematode was already in Queensland and that it was important for growers to keep and eye out for signs.

“We have other (types of) root-knot nematodes in sweet potato and they’re seen as number one or number two in terms of pests and diseases on the roots, and because they’re in the soil they’re more difficult to manage.”

Queensland farmers concerned

With the threat right on their doorstep, Queensland’s sweet potato growers feel they have been left in the dark.

Wolfies Farms is a major sweet potato producer based in Rossmoya, near Rockhampton in Central Queensland. 

Manager Rodney Wolfenden said he was taken by surprise by the news of the pest.

man stares into camera
Farmer Rodney Wolfenden feels left in the dark about the pest.(Supplied: Rodney Wolfenden)

“I’m not familiar with it at all, it’s not something that we’ve had here previously” he said.

Mr Wolfenden first heard about the pest from a fellow member of the sweet potato industry and said he was yet to receive contact from the Department of Agriculture and Fisheries.

“There has been no contact from the department, the only thing that we’ve seen is a press release, but essentially no information about it — nothing,” he said.

Mr Wolfenden said he was unsure of his next steps.

“I’d like to think that there are attempts made to eradicate it or at least contain it — I’m pretty disappointed that it’s there,” he said.

“The only good thing I can see … is that it has actually been spotted and now we can do something about it.”

Mr Wolfenden said it was the last thing the industry needed.

“We’ve been through a hard time over the last couple of years, we don’t need something like this to turn up,” he said.

“It’s going to affect a wide range of other crops as well — no one needs that sort of thing.”

Farmers urged to report suspected cases

In a statement provided to the ABC, Biosecurity Queensland urged growers in the state to remain vigilant.

“Guava root-knot nematode is a significant threat to horticultural industries as it can be more destructive than other root-knot species on many crops,” it said.

“The risk of spread from the Northern Territory into Queensland and other jurisdictions for plant products and commodities currently traded is considered very low, although the risk for nursery plants is likely to be higher.”

Farmers with suspected guava root-knot nematode on their property were told to report it immediately to Biosecurity Queensland on 13 25 23, online at daf.qld.gov.au or to the Exotic Plant Pest Hotline on 1800 084 881.

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