Cyprocide selectively kills nematodes via cytochrome P450 bioactivation.

Left unchecked, plant-parasitic nematodes have the potential to devastate crops globally. Highly effective but non-selective nematicides are justifiably being phased-out, leaving farmers with limited options for managing nematode infestation. Here, we report our discovery of a 1,3,4-oxadiazole thioether scaffold called Cyprocide that selectively kills nematodes including diverse species of plant-parasitic nematodes. Cyprocide is bioactivated into a lethal reactive electrophilic metabolite by specific nematode cytochrome P450 enzymes. Cyprocide fails to kill organisms beyond nematodes, suggesting that the targeted lethality of this pro-nematicide derives from P450 substrate selectivity. Our findings demonstrate that Cyprocide is a selective nematicidal scaffold with broad-spectrum activity that holds the potential to help safeguard our global food supply.

First report of Meloidogyne hapla on hemp (Cannabis sativa) in Oregon.

Hemp is a crop that has gained interest in Washington and Oregon. As with other crops, hemp production faces challenges due to biotic factors, including plant-parasitic nematodes. During a survey for plant-parasitic nematodes associated with hemp, Meloidogyne sp. was found in a composite root sample collected in Oregon. Morphological characterization of second-stage juveniles identified the nematode as Meloidogyne hapla. Molecular identification confirmed the population as M. hapla. To our knowledge, this is the first report of M. hapla on hemp in the Pacific Northwest of the United States.

Direct sequencing of insect symbionts via nanopore adaptive sampling.

Insect symbionts can alter their host phenotype and their effects can range from beneficial to pathogenic. Moreover, many insects exhibit co-infections, making their study more challenging. Less than 1% of insect species have high-quality referenced genomes available and fewer still also have their symbionts sequenced. Two methods are commonly used to sequence symbionts: whole-genome sequencing to concomitantly capture the host and bacterial genomes, or isolation of the symbiont's genome before sequencing. These methods are limited when dealing with rare or poorly characterized symbionts. Long-read technology is an important tool to generate high-quality genomes as they can overcome high levels of heterozygosity, repeat content, and transposable elements that confound short-read methods. Oxford Nanopore (ONT) adaptive sampling allows a sequencing instrument to select or reject sequences in real time. We describe a method based on ONT adaptive sampling (subtractive) approach that readily permitted the sequencing of the complete genomes of mitochondria, Buchnera and its plasmids (pLeu, pTrp), and Wolbachia genomes in two aphid species, Aphis glycines and Pentalonia nigronervosa. Adaptive sampling is able to retrieve organelles such as mitochondria and symbionts that have high representation in their hosts such as Buchnera and Wolbachia, but is less successful at retrieving symbionts in low concentrations.

NILR1 perceives a nematode ascaroside triggering immune signaling and resistance.

Plants use pattern recognition receptors (PRRs) to perceive conserved molecular patterns derived from pathogens and pests, thereby activating a sequential set of rapid cellular immune responses, including activation of mitogen-activated protein kinases (MAPKs) and Ca2+-dependent protein kinases (CDPKs), transcriptional reprogramming (particularly the induction of defense-related genes), ion fluxes, and production of reactive oxygen species.1 Plant PRRs belong to the multi-membered protein families of receptor-like kinases (RLKs) or receptor-like proteins (RLPs). RLKs consist of a ligand-binding ectodomain, a single-pass transmembrane domain, and an intracellular kinase domain, while RLPs possess the same functional domains, except for the intracellular kinase domain.2 The most abundant nematode ascaroside, Ascr18, is a nematode-associated molecular pattern (NAMP) that induces immune signaling and enhances resistance to pathogens and pests in various plant species.3 In this study, we found that the Arabidopsis NEMATODE-INDUCED LRR-RLK1 (NILR1) protein4 physically interacts with the Ascr18 elicitor, as indicated by a specific direct interaction between NILR1 and Ascr18, and NILR1 is genetically required for Ascr18-triggered immune signaling and resistance to both bacterium and nematode, as manifested by the abolishment of these immune responses in the nilr1 mutant. These results suggest that NILR1 is the immune receptor of the nematode NAMP Ascr18, mediating Ascr18-triggered immune signaling and resistance to pathogens and pests.

Selective control of parasitic nematodes using bioactivated nematicides.

Parasitic nematodes are a major threat to global food security, particularly as the world amasses 10 billion people amid limited arable land1-4. Most traditional nematicides have been banned owing to poor nematode selectivity, leaving farmers with inadequate means of pest control4-12. Here we use the model nematode Caenorhabditis elegans to identify a family of selective imidazothiazole nematicides, called selectivins, that undergo cytochrome-p450-mediated bioactivation in nematodes. At low parts-per-million concentrations, selectivins perform comparably well with commercial nematicides to control root infection by Meloidogyne incognita, a highly destructive plant-parasitic nematode. Tests against numerous phylogenetically diverse non-target systems demonstrate that selectivins are more nematode-selective than most marketed nematicides. Selectivins are first-in-class bioactivated nematode controls that provide efficacy and nematode selectivity.

The Hop Cyst Nematode, Heterodera humuli: History, Distribution, and Impact on Global Hop Production.

Humulus lupulus (commonly known as hop) is an herbaceous plant that is used in brewing throughout the world. Hop cones are an essential ingredient in the production of beer, which makes hops of critical importance to global craft beverage industries. The hop cyst nematode, Heterodera humuli, is a plant-parasitic nematode with the potential to substantially limit yields of hop. H. humuli has been detected in many of the most significant regions for hop production worldwide, and infestations of H. humuli can consequently impact hop growth and limit cone production. Despite documented reports on the distribution of and damage caused by H. humuli since its description in 1934, there have been limited studies on the biology, pathogenicity, management, and consequences of infestations on hop production over time. Inconsistencies and gaps in the available information (e.g., the number of H. humuli generations per season, host status of alternate crops), exacerbate difficulties in understanding how H. humuli can be managed. Resolving the existing knowledge gaps identified within this review can lead to determining effective H. humuli management strategies for hop growers.

Egg-laying and locomotory screens with C. elegans yield a nematode-selective small molecule stimulator of neurotransmitter release.

Nematode parasites of humans, livestock and crops dramatically impact human health and welfare. Alarmingly, parasitic nematodes of animals have rapidly evolved resistance to anthelmintic drugs, and traditional nematicides that protect crops are facing increasing restrictions because of poor phylogenetic selectivity. Here, we exploit multiple motor outputs of the model nematode C. elegans towards nematicide discovery. This work yielded multiple compounds that selectively kill and/or immobilize diverse nematode parasites. We focus on one compound that induces violent convulsions and paralysis that we call nementin. We find that nementin stimulates neuronal dense core vesicle release, which in turn enhances cholinergic signaling. Consequently, nementin synergistically enhances the potency of widely-used non-selective acetylcholinesterase (AChE) inhibitors, but in a nematode-selective manner. Nementin therefore has the potential to reduce the environmental impact of toxic AChE inhibitors that are used to control nematode infections and infestations.

Genome Announcement: The Draft Genome of the Carrot Cyst Nematode Heterodera Carotae.

Heterodera carotae, the carrot cyst nematode, is a significant pest affecting carrot globally. Here we present the draft genome of H. carotae, which was generated from short read libraries from Illumina HiSeq technology, and the corresponding genome annotation.

What is the Optimal Way to Assess Meloidogyne Spp. Reproduction in Greenhouse Pot Experiments?

Often research efforts that address both the practical concerns of managing Meloidogyne spp. and understanding their basic biology involve greenhouse reproduction assays. However, there is little consensus in regards to what parameters should be used to conduct greenhouse assays. The goal of this research was to evaluate how pot size, Meloidogyne spp. inoculation life stage, inoculation density, and time of assay impacted final reproduction factor (RF = initial nematode density/final nematode density) values. In experiments with M. incognita, the factor of the pot size mattered, with higher RF values in pots containing 500 g soil vs. pots with 100 g soil; larger pots containing 3,000 g soil did not have RF values different from the aforementioned sizes. Inoculating with M. incognita J2 resulted in RF values on average of >2 fold higher then when inoculating with eggs at comparable densities. Inoculation density of M. incognita did not have an impact on final M. incognita RF values. In experiments that considered time of assay, three species were evaluated: M. incognita, M. chitwoodi, and M. hapla. There was no difference in M. incognita RF values when assays were conducted for 5 wk, 6 wk, 7 wk, and 8 wk. However, a longer assay time resulted in higher RF values for M. hapla and M. chitwoodi, with at least a 7 week assay required. In conclusion, a moderate pot size (500 g of soil) inoculated with M. incognita J2 resulted in maximum RF values. The length of the assay required will depend on the Meloidogyne spp. in question, with longer duration assays required for M. hapla and M. chitwoodi than for M. incognita.

Transcriptional response of Meloidogyne incognita to non-fumigant nematicides.

There is limited research about the impacts of new nematicides, including fluazaindolizine, fluopyram, and fluensulfone, on the plant-parasitic nematode Meloidogyne incognita, despite it being a pervasive agricultural pest. In this study, M. incognita second-stage juveniles were exposed for 24-h to fluensulfone, fluazaindolizine, fluopyram, and oxamyl and total RNA was extracted and sequenced using next-generation sequencing to determine gene expression. The effects of nematicide exposure on cellular detoxification pathways, common differentially expressed (DE) genes, and fatty acid and retinol-binding genes were examined. Fluopyram and oxamyl had the smallest impacts on the M. incognita transcriptome with 48 and 151 genes that were DE, respectively. These compounds also elicited a weak response in the cellular detoxification pathway and fatty acid and retinol-binding (FAR) genes. Fluensulfone and fluazaindolizine produced robust transcriptional responses with 1208 and 2611 DE genes, respectively. These compounds had strong impacts on cellular detoxification, causing differential regulation of transcription factors and genes in the detox pathway. These compounds strongly down-regulated FAR genes between 52-85%. Having a greater understanding of how these compounds function at a molecular level will help to promote proper stewardship, aid with nematicide discovery, and help to stay a step ahead of nematicide resistance.

Transcriptional changes of biochemical pathways in Meloidogyne incognita in response to non-fumigant nematicides.

Meloidogyne incognita is a destructive and economically important agricultural pest. Similar to other plant-parasitic nematodes, management of M. incognita relies heavily on chemical controls. As old, broad spectrum, and toxic nematicides leave the market, replacements have entered including fluensulfone, fluazaindolizine, and fluopyram that are plant-parasitic nematode specific in target and less toxic to applicators. However, there is limited research into their modes-of-action and other off-target cellular effects caused by these nematicides in plant-parasitic nematodes. This study aimed to broaden the knowledge about these new nematicides by examining the transcriptional changes in M. incognita second-stage juveniles (J2) after 24-h exposure to fluensulfone, fluazaindolizine, and fluopyram as well as oxamyl, an older non-fumigant nematicide. Total RNA was extracted and sequenced using Illumina HiSeq to investigate transcriptional changes in the citric acid cycle, the glyoxylate pathway, [Formula: see text]-fatty acid oxidation pathway, oxidative phosphorylation, and acetylcholine neuron components. Observed transcriptional changes in M. incognita exposed to fluopyram and oxamyl corresponded to their respective modes-of-action. Potential targets for fluensulfone and fluazaindolizine were identified in the [Formula: see text]-fatty acid oxidation pathway and 2-oxoglutarate dehydrogenase of the citric acid cycle, respectively. This study provides a foundation for understanding how potential nematicide resistance could develop, identifies cellular pathways as potential nematicide targets, and determines targets for confirming unknown modes-of-action.

Targeted transcriptomics reveals signatures of large-scale independent origins and concerted regulation of effector genes in Radopholus similis.

The burrowing nematode, Radopholus similis, is an economically important plant-parasitic nematode that inflicts damage and yield loss to a wide range of crops. This migratory endoparasite is widely distributed in warmer regions and causes extensive destruction to the root systems of important food crops (e.g., citrus, banana). Despite the economic importance of this nematode, little is known about the repertoire of effectors owned by this species. Here we combined spatially and temporally resolved next-generation sequencing datasets of R. similis to select a list of candidates for the identification of effector genes for this species. We confirmed spatial expression of transcripts of 30 new candidate effectors within the esophageal glands of R. similis by in situ hybridization, revealing a large number of pioneer genes specific to this nematode. We identify a gland promoter motif specifically associated with the subventral glands (named Rs-SUG box), a putative hallmark of spatial and concerted regulation of these effectors. Nematode transcriptome analyses confirmed the expression of these effectors during the interaction with the host, with a large number of pioneer genes being especially abundant. Our data revealed that R. similis holds a diverse and emergent repertoire of effectors, which has been shaped by various evolutionary events, including neofunctionalization, horizontal gene transfer, and possibly by de novo gene birth. In addition, we also report the first GH62 gene so far discovered for any metazoan and putatively acquired by lateral gene transfer from a bacterial donor. Considering the economic damage caused by R. similis, this information provides valuable data to elucidate the mode of parasitism of this nematode.

Genomic Analyses of Globodera pallida, A Quarantine Agricultural Pathogen in Idaho.

Globodera pallida is among the most significant plant-parasitic nematodes worldwide, causing major damage to potato production. Since it was discovered in Idaho in 2006, eradication efforts have aimed to contain and eradicate G. pallida through phytosanitary action and soil fumigation. In this study, we investigated genome-wide patterns of G. pallida genetic variation across Idaho fields to evaluate whether the infestation resulted from a single or multiple introduction(s) and to investigate potential evolutionary responses since the time of infestation. A total of 53 G. pallida samples (~1,042,000 individuals) were collected and analyzed, representing five different fields in Idaho, a greenhouse population, and a field in Scotland that was used for external comparison. According to genome-wide allele frequency and fixation index (Fst) analyses, most of the genetic variation was shared among the G. pallida populations in Idaho fields pre-fumigation, indicating that the infestation likely resulted from a single introduction. Temporal patterns of genome-wide polymorphisms involving (1) pre-fumigation field samples collected in 2007 and 2014 and (2) pre- and post-fumigation samples revealed nucleotide variants (SNPs, single-nucleotide polymorphisms) with significantly differentiated allele frequencies indicating genetic differentiation. This study provides insights into the genetic origins and adaptive potential of G. pallida invading new environments.

Phytoparasitic nematodes of organic vegetables in the Argan Biosphere of Souss-Massa (Southern Morocco).

Agroecological productivity of the Arganeraie Biosphere Reserve of Morocco is limited by the wide spread and dynamics of plant parasitic nematodes (PPN). Ecological studies of nematode communities are required to develop effective biological management of these bioagressors as conventional control methods of PPN are inadequate and have persistent harmful effects. Fifty-nine organic vegetable soils in Souss-Massa were nematologically sampled, and assessment of taxonomic proliferation was made in relation to host species, geographical origin, and climatic and microclimatic factors. Twenty-four nematode genera were identified as obligate and facultative plant feeders. Taxonomic diversity increased from Chtouka to Taroudant and Tiznit provinces. Soil texture, organic matter, pH, nitrogen, zinc, magnesium, copper, altitude, and humidity and temperature were seen to effect driving roles in the abundance, distribution, and community structures of nematodes. The most prevalent taxa posing a high risk to organic agriculture of Souss Massa were needle nematodes (Longidorus spp.) and root-knot nematodes (Meloidogyne spp.). Edaphic and climatic variables effected nematode populations greatly. A combination of biological treatments and appropriate agroecological practices restricting important economic PPN growth and enhancing soil quality are required to achieve sustainable management in the area.

Growth, Sporulation, and Pathogenicity of the Raspberry Pathogen Phytophthora rubi Under Different Temperature and Moisture Regimes.

Phytophthora root rot of raspberry, which is mostly caused by Phytophthora rubi, is a significant issue for the Washington State red raspberry industry. Considered a cool weather pathogen, it is often assumed that it is most active and infective during the cool, wet winters of the region when soil temperatures range from 5 to 10°C; however, there are little data to support this view. More recent research has found that symptoms of root disease during late summer were strongly associated with P. rubi. Therefore, experiments were conducted at four temperatures from 5 to 20°C to evaluate the effects of temperature on P. rubi mycelial growth and sporulation and the effects of both temperature and soil moisture on the pathogenicity of P. rubi on red raspberry. At 20°C, P. rubi grew fastest and sporulated the most heavily. However, disease was most severe at both 15 and 20°C. The soil moisture parameters tested did not affect the pathogenicity results. These results show that P. rubi is more likely to infect during the spring and summer months (from May through September), when soil temperatures are consistently in the range of 15 to 20°C.

First Report of the Hop Cyst Nematode, Heterodera humuli, in Two Counties of the Yakima Valley Region, WA, USA.

Cyst nematodes are ranked as the second most damaging plant-parasitic nematode genus of crops worldwide (Jones et al. 2013). The hop cyst nematode, Heterodera humuli, has been reported to cause up to 38% reduction in dry hops per bine (Hay and Pethybridge 2003). America is the top hop producing country worldwide, with 75% of production occurring in Washington state, with the majority of this production occurring in the Yakima Valley region (USDA, 2019). In late 2019, 30 soil samples from 15 different fields were collected from the hop cvs. HBC 394, HBC 369, and YCR 14. Nematodes were extracted using an adapted centrifugal floatation method (Jenkins 1964) from 100 cc subsamples of soil. Twenty of these samples contained at least one cyst and 23 contained at least one juvenile. Body length of juveniles (n = 5) averaged + standard deviation 377.62 ± 4.76 µm which is consistent with H. humuli juvenile body measurements (Sen 1968). Three samples from Yakima County and two from Benton County were identified to the species level using sequences from the internal transcribed spacer (ITS) region of the 5.8S gene. The sequences (GenBank accession numbers MT840678 to MT840682) were amplified using forward primer 5.8S-F (5'-GTGATTCCATTCACCAHCTACCTG-3'), and reverse primer 5.8S-R (5'-TTCGCACTAATTATCGCAGTTGG-3'). Sequence comparison with available ITS (5.8S) sequences in GenBank using BLAST showed 99.85% identity to H. humuli for all five samples. Because COI sequences of H. humuli are not available, to provide an additional marker for species identification, we amplified the COI sequences by using (forward primer Hete-COI-F (5'-TTTGGDCAYCCHGARGTTTATGTT-3'), and reverse primer Hete-COI-R (5'-AYWGTAAAAAGGRRAATAAAACC-3') for these samples. Four COI sequences (GenBank accession numbers MT840683 to MT840686) were obtained. These COI sequences will be used to identify future H. humuli samples. To confirm pathogenicity, eight 1-gal pots were filled with a 90:10 play sand to potting soil mixture and one hop rhizome cv. 'Centennial' was planted in pots and maintained in a greenhouse. After above ground plant growth was observed, half the pots were inoculated with hand-picked H. humuli cysts from Yakima soil samples at a density of 10 cysts/100 cc of soil. The life cycle of H. humuli in potted experiments is 40 days (McNamara and Mende 1995). Forty-five days after inoculation, plant measurements were recorded and nematodes extracted from five 100 cc soil samples per pot as described above. Soil samples revealed that H. humuli populations had an average Reproductive Factor (RF = final nematode population/initial nematode population) of 2.08. Five cysts were crushed to determine eggs/cyst, which yielded an average of 101 eggs/cyst. Young infected hops lacked vigor, with all replicates stunted both in bine height and leaf length compared to healthy controls. Bine heights were reduced by an average of 40.4% in pots inoculated with H. humuli compared to control plants (P = 0.0016). Distribution of hop cyst within the United States is limited to the top four states for hop production: Washington, Oregon, Idaho and Michigan (Cobb 1962; Sen and Jensen 1967; Hafez et al. 2010, Warner and Bird, 2015). In 1962, Cobb reported H. humuli in Pierce County, Washington, but it had not been reported in Benton County and Yakima County until now. This is a significant finding that has the potential to impact the Washington state hop industry, valued at $475.7 million in 2019 (USDA, 2019). Due to the lack of known effective nematode control measures, the discovery of H. humuli in the major hop-growing region of Washington warrants concern.

Differential Response of Meloidogyne, Pratylenchus, Globodera, and Xiphinema Species to the Nematicide Fluazaindolizine.

This research focused on the effects of fluazaindolizine on a diversity of plant-parasitic nematodes. In microwell assays, 24-h dose-response curves were generated for several species and populations of Meloidogyne, Pratylenchus neglectus, P. penetrans, Globodera ellingtonae, and Xiphinema americanum. In a greenhouse study, the impact of fluazaindolizine on fecundity of M. incognita, M. hapla, and M. chitwoodi was tested by exposing nematodes for 24 h in solution and inoculating on tomato. The average 24-h ED50s (dose that resulted in the immobility of 50% of exposed nematodes) for M. hapla, M. chitwoodi, and M. incognita were 325.7, 223.4, and 100.7 ppm, respectively. M. hapla had the most variation among populations, with 24-h ED50s ranging from 72 to 788 ppm. G. ellingtonae had the lowest 24-h ED50 at 30 ppm. Pratylenchus spp. were unaffected by fluazaindolizine. X. americanum was the only species where effects of fluazaindolizine were reversible, but had a 24-h ED50 that fell in the range of the Meloidogyne spp. In the greenhouse study, M. chitwoodi was the least sensitive with reproduction reaching 62% of the untreated control after a pre-exposure to 47 ppm, whereas M. incognita and M. hapla at the same exposure dose had reproduction rates of 27 and 36% of the untreated control, respectively. Despite varying in in vitro responses to fluazaindolizine, reproduction of all Meloidogyne spp. was suppressed after only 24 h of exposure. This study expanded our understanding of how G. ellingtonae, P. thornei, P. penetrans, and X. americanum respond to fluazaindolizine.

Prevalence of the root lesion nematode virus (RLNV1) in populations of Pratylenchus penetrans from North America.

Root lesion nematode virus 1 (RLNV1) was discovered in the migratory endoparasitic nematode species Pratylenchus penetrans. It was found in a P. penetrans population collected from soil samples in Beltsville, Maryland, USA. In this study, the distribution of the RLNV1 in 31 geographically distinct P. penetrans populations obtained from different crops was examined. The results demonstrate that RLNV1 is widespread in North American populations of P. penetrans and exhibits low genetic variability in the helicase and RNA-dependent RNA polymerase regions of the genome.Root lesion nematode virus 1 (RLNV1) was discovered in the migratory endoparasitic nematode species Pratylenchus penetrans. It was found in a P. penetrans population collected from soil samples in Beltsville, Maryland, USA. In this study, the distribution of the RLNV1 in 31 geographically distinct P. penetrans populations obtained from different crops was examined. The results demonstrate that RLNV1 is widespread in North American populations of P. penetrans and exhibits low genetic variability in the helicase and RNA-dependent RNA polymerase regions of the genome.

Directed energy system technology for the control of soilborne fungal pathogens and plant-parasitic nematodes.

BACKGROUND: It is challenging to manage soilborne pathogens and plant-parasitic nematodes using sustainable practices. Here, we evaluated a novel energy application system, Directed Energy System (DES). This system generates pulses of energy capable of impacting selected biological organisms. The oomycete Phytophthora cinnamomi, the fungus Verticillium dahliae, and the plant-parasitic nematodes Meloidogyne hapla and Globodera ellingtonae were added to soil. Then DES-generated energy was applied to soil and impacts on target organisms were determined. RESULTS: DES applied at 20, 40 and 70 J cm-3 to P. cinnamomi and V. dahliae resulted in ≥50% and 92% reductions (respectively) of propagules per gram of soil in comparison to the untreated control. There was a significant reduction of M. hapla eggs per gram of host tomato root between the untreated control, and 2.2, 13 and 25 J cm-3 DES dosages applied pre- or post-planting. Additionally, an 84% reduction in hatch from G. ellingtonae encysted eggs after treatment with 70 J cm-3 DES was observed. The dosages ranged from 40 or 80V mm-1 for nematodes to 200 V mm-1 for fungi. CONCLUSION: DES-generated energy reduced survival of the soilborne pathogens P. cinnamomi and V. dahlia, and the plant-parasitic nematodes M. hapla and G. ellingtonae. The application of this technology to a field setting remains to be considered. Published 2020. This article is a U.S. Government work and is in the public domain in the USA. Pest Management Science published by Wiley Periodicals, Inc. on behalf of © 2020 Society of Chemical Industry.

New reduced-risk agricultural nematicides - rationale and review.

The last decade has seen a sharp increase in nematicide research in the agricultural industry. As a result, several new synthetic nematicides have become available to growers, and several more are expected in the near future. This new interest in nematicides is directly related to the growing demand for safer and more selective products, and the increasing regulatory pressure on many of the traditional nematicides. This has led to a ban of several widely used fumigant (e.g. methyl bromide) and non-fumigant (e.g. aldicarb) nematicides. The loss of traditional nematicides, combined with a lack of replacement products and awareness of the damage that nematodes can cause, has not only raised concern among growers, but has also created new opportunities for the crop protection industry. Nematicides have become a priority, and many companies are now allocating significant research dollars to discover new nematicides. The new nematicides are very different from previous products: (i) they are more selective, often only targeting nematodes, and (ii) they are less toxic, and safer to use. This review article describes these new developments by discussing the challenges that are associated with finding new nematicides, reviewing the nature, characteristics, and efficacy of new nematicides, and discussing the impact they could have on future nematode management.