Effect of Foliarly Applied Spirotetramat on Reproduction of Heterodera avenae on Wheat Roots

Resistance and Tolerance Screening of Spring Wheat Cultivars to Cereal Cyst Nematode (Heterodera avenae) in Southeastern Idaho

Increased populations of Heterodera avenae in southeastern Idaho are associated with increased planting of susceptible cereal cultivars and lack of crop rotation. Identifying high-yield, resistant spring wheat cultivars with tolerance requires testing new genotypes and susceptibility assessments of marketed cultivars. We conducted two experiments to determine whether cultivars with putative resistance could maintain acceptable yield in the presence of H. avenae. We also evaluated the tolerance response in relation to previously tested cultivars. Seven spring wheat cultivars were planted in two irrigated commercial fields that were naturally infested with high populations of H. avenae. Measures of resistance, tolerance, and grain yield were assessed in aldicarb-treated versus nontreated plots. In aldicarb-treated plots in both years, grain yield of the susceptible cultivars Snow Crest, WestBred 936, WB9411, Patwin-515, and WB9668 was significantly increased. The expected yield increase with aldicarb was limited for the moderately susceptible Expresso due to water stress. 'WB-Rockland', carrying the Cre5 resistance gene, maintained its standard yield, while none of the other cultivars in the experiment showed resistance or tolerance. Our results indicated that aldicarb improves wheat grain yield in irrigated crop production systems, and although removed from the market, it is effective and has utility for research. The results also support the hypothesis that high yield susceptible cultivars can mask the effect of H. avenae on grain yield when managed appropriately.

Dissipation kinetics and exposure of spirotetramat and pymetrozine in open fields, a prelude to risk assessment of green bean consumption

Determination and dissipation kinetics of pymetrozine and spirotetramat in green bean were studied using a QuEChERS method coupled to high-performance liquid chromatography-tandem mass spectrometry. Pymetrozine recoveries ranged between 88.4-93.7%, with relative standard deviation (RSD) of 5.5-14.4%. For spirotetramat the recoveries ranged between 91.7-103.4%, and the RSD were in the range of 3.2 to 12.4%. The limits of quantification (LOQs) were 0.01 mg/kg and 0.005 mg/kg for pymetrozine and spirotetramat, respectively.The developed analytical method was used to study the degradation rates of pymetrozine and spirotetramat in green bean grown in open field. Results showed that pymetrozine and spirotetramat followed the first-order kinetics model with half-lives of 3.3 days and 4.2 days, respectively. Furthermore, risk assessment was carried out which showed that, the chronic risk quotient (RQc) values for pymetrozine and spirotetramat were much lower than 100%. The present results indicated that the health risks posed for consumers by the pymetrozine and spirotetramat residues were negligible at the recommended dosages.

The spirotetramat inhibits growth and reproduction of silkworm by interfering with the fatty acid metabolism

Spirotetramat is a novel insecticide and acaricide that can effectively control many species of piercing-sucking pests by inhibiting lipid synthesis. The silkworm is an economically important insect and a model organism for genetics and biochemical research. However, the toxic effect on their development and reproduction remain unclear. In this study, we demonstrated the negative effects of spirotetramat on the development, vitality, silk protein synthesis, and fecundity of silkworm. We also compared expression changes of silkworm genes using digital gene expression (DGE). A total of 1567 differentially expressed genes (DEGs) were detected, of which 874 genes were downregulated and 693 genes were upregulated. Gene Ontology (GO) enrichment analysis showed that the DEGs were enriched in the oxidation-reduction process, oxidoreductase activity, and fatty-acyl-CoA reductase activity. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the DEGs were mainly enriched in fatty acid metabolism and lysosome pathways. We detected the relative expression of silkworm genes related to fatty acid synthesis and decomposition pathways and the degradation pathway of juvenile hormone by quantitative real-time PCR. The expression levels of Acetyl CoA carboxylase (ACC), fatty acyl-CoA reductase (FACR), Enoyl-CoA hydratase (ECH), very-long-chain (3R)-3-hydroxyacyl-CoA dehydratase (LCHAD), juvenile hormone epoxide hydrolase (JHEH), and phytanoyl-CoA dioxygenase (PCD) genes were downregulated. These data demonstrate the effects of spirotetramat on silkworm and its effects on genes involved in fatty acid metabolism.

Control of foliar phytoparasitic nematodes through sustainable natural materials: Current progress and challenges

Nematodes are hidden enemies that inhibit the entire ecosystem causing adverse effects on animals and plants, leading to economic losses. Management of foliar phytoparasitic nematodes is an excruciating task. Various approaches were used to control nematodes dispersal, i.e., traditional practices, resistant cultivars, plant extract, compost, biofumigants, induced resistance, nano-biotechnology applications, and chemical control. This study reviews the various strategies adopted in combating plant-parasitic nematodes while examining the benefits and challenges. The significant awareness of biological and environmental factors determines the effectiveness of nematode control, where the incorporation of alternative methods to reduce the nematodes population in plants with increasing crop yield. The researchers were interested in explaining the fundamental molecular mechanisms, providing an opportunity to deepen our understanding of the sustainable management of nematodes in croplands. Eco-friendly pesticides are effective as a sustainable nematodes management tool and safe for humans. The current review presents the eco-friendly methods in controlling nematodes to minimize yield losses, and benefit the agricultural production efficiency and the environment.

From Old-Generation to Next-Generation Nematicides

The phaseout of methyl bromide and the ban on, or withdrawal of, other toxic soil fumigants and non-fumigant nematicides belonging to the organophosphate and carbamate groups are leading to changes in nematode-control strategies. Sustainable nematode-control methods are available and preferred, but not always effective enough, especially for cash crops in intensive agriculture. A few non-fumigant nematicides, which have a relatively high control efficacy with a low toxicity to non-target organisms, have been released to the market or are in the process of being registered for use. Fluensulfone, fluopyram, and fluazaindolizine are the three main and most promising next-generation nematicides. In this paper, several aspects of these non-fumigant nematicides are reviewed, along with a brief history and problems of old-generation nematicides.

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.

Inhibition of acetyl-CoA carboxylase by spirotetramat causes growth arrest and lipid depletion in nematodes

Plant-parasitic nematodes pose a significant threat to agriculture causing annual yield losses worth more than 100 billion US$. Nematode control often involves the use of nematicides, but many of them including non-selective fumigants have been phased out, particularly due to ecotoxicological concerns. Thus new control strategies are urgently needed. Spirotetramat (SPT) is used as phloem-mobile systemic insecticide targeting acetyl-CoA carboxylase (ACC) of pest insects and mites upon foliar application. However, in nematodes the mode of action of SPT and its effect on their development have not been studied so far. Our studies revealed that SPT known to be activated in planta to SPT-enol acts as a developmental inhibitor of the free-living nematode Caenorhabditis elegans and the plant-parasitic nematode Heterodera schachtii. Exposure to SPT-enol leads to larval arrest and disruption of the life cycle. Furthermore, SPT-enol inhibits nematode ACC activity, affects storage lipids and fatty acid composition. Silencing of H. schachtii ACC by RNAi induced similar phenotypes and thus mimics the effects of SPT-enol, supporting the conclusion that SPT-enol acts on nematodes by inhibiting ACC. Our studies demonstrated that the inhibition of de novo lipid biosynthesis by interfering with nematode ACC is a new nematicidal mode of action addressed by SPT, a well-known systemic insecticide for sucking pest control.

Distribution of Cereal Cyst Nematodes (Heterodera avenae and H. filipjevi) in Eastern Washington State

Cereal cyst nematodes (CCN; Heterodera avenae and H. filipjevi), cause substantial worldwide yield loss in small grain cereals such as wheat, barley, and oat. H. avenae was first detected in the United States in western Oregon in 1974 and had spread to northeast Oregon by the mid-1980s. Although H. avenae was detected in eastern Washington in 1984, extensive infestations were not recognized until 2010. H. filipjevi, first detected in Oregon in 2008, was found in eastern Washington in 2014. To gain more information about the distribution of these two species, an extensive survey was undertaken in eastern Washington, and methods were developed to distinguish species using DNA sequencing of single cysts. In this study, we surveyed 356 wheat and barley fields in eastern Washington from 2007 to 2017. CCN from the infested locations were identified to species level by sequencing the ribosomal internal transcribed spacers (ITS) and/or 28S ribosomal RNA (rRNA) genes. The sequences were compared in the GenBank database in the National Center for Biotechnology Information (NCBI) to identify species. The results show that H. filipjevi is primarily confined to southern Whitman County, WA; and H. avenae has a wider distribution across the higher precipitation annual cropping area of eastern Whitman County. Knowledge of species identification is critical for deployment of host resistance as an effective means of management, since resistance genes for one species of CCN may not be effective against the other.

Effect of spirotetramat and fluensulfone on population densities of Mesocriconema xenoplax and Meloidogyne incognita on peach

Management of plant-parasitic nematodes (PPNs) on peach is needed for a longer period of time than is typically afforded by pre-plant fumigant nematicides. Two post-plant nematicides, spirotetramat and fluensulfone, were evaluated for control of Meloidogyne incognita and Mesocriconema xenoplax under laboratory and greenhouse conditions. In vitro assays were conducted to test the effect of spirotetramat at 0.017 and 0.026 kg a.i./ha and fluensulfone at 3.92 kg a.i./ha on the mobility of both M. incognita and M. xenoplax in 24-well plates for 24, 48, and 72 hr, compared to a water control. Both fluensulfone and spirotetramat reduced mobility of M. xenoplax, but only fluensulfone reduced the mobility of M. incognita, compared to the untreated control. In peach greenhouse trials, both spirotetramat at 0.017 kg a.i./ha and fluensulfone at 3.92 kg a.i./ha reduced M. incognita numbers by 62 and 77% at 40 d after inoculation (DAI), respectively; neither chemical reduced populations at 70 DAI. Fluensulfone reduced M. xenoplax numbers by 84, 94, and 96% at 30, 60, and 90 DAI, respectively. No effects were observed for spirotetramat on M. xenoplax. At 40 DAI, dual applications of spirotetramat 30 d apart reduced M. incognita numbers by 58 and 54% for both 0.017 and 0.026 kg a.i./ha rates, respectively; no reductions were observed at 70 DAI. No effect was seen for a dual application of spirotetramat on M. xenoplax. These post-plant nematicides may provide additional options for management of PPNs on peach.

Management of plant-parasitic nematodes (PPNs) on peach is needed for a longer period of time than is typically afforded by pre-plant fumigant nematicides. Two post-plant nematicides, spirotetramat and fluensulfone, were evaluated for control of Meloidogyne incognita and Mesocriconema xenoplax under laboratory and greenhouse conditions. In vitro assays were conducted to test the effect of spirotetramat at 0.017 and 0.026 kg a.i./ha and fluensulfone at 3.92 kg a.i./ha on the mobility of both M. incognita and M. xenoplax in 24-well plates for 24, 48, and 72 hr, compared to a water control. Both fluensulfone and spirotetramat reduced mobility of M. xenoplax, but only fluensulfone reduced the mobility of M. incognita, compared to the untreated control. In peach greenhouse trials, both spirotetramat at 0.017 kg a.i./ha and fluensulfone at 3.92 kg a.i./ha reduced M. incognita numbers by 62 and 77% at 40 d after inoculation (DAI), respectively; neither chemical reduced populations at 70 DAI. Fluensulfone reduced M. xenoplax numbers by 84, 94, and 96% at 30, 60, and 90 DAI, respectively. No effects were observed for spirotetramat on M. xenoplax. At 40 DAI, dual applications of spirotetramat 30 d apart reduced M. incognita numbers by 58 and 54% for both 0.017 and 0.026 kg a.i./ha rates, respectively; no reductions were observed at 70 DAI. No effect was seen for a dual application of spirotetramat on M. xenoplax. These post-plant nematicides may provide additional options for management of PPNs on peach.

Adsorption and Desorption Behaviors of Spirotetramat in Various Soils and Its Interaction Mechanism

Spirotetramat is a pesticide with bidirectional systemicity and can effectively control pests by inhibiting the biosynthesis of fatty acids. In this study, adsorption and desorption behaviors of spirotetramat in six soils and its interaction mechanism were studied using the batch equilibrium method and infrared radiation. The results showed that the adsorption and desorption behaviors of spirotetramat conformed to the Freundlich isotherm model. The values of adsorption capacities K_F-ads ranged from 2.11 to 12.40, and the values of desorption capacities K_F-des varied from 2.97 to 32.90. From the hysteresis coefficient, spirotetramat was easily desorbed from the test soils. The adsorption capacity of the soil to spirotetramat enhanced with an increasing temperature. Moreover, the changes in pH values and exogenous addition of humic acid and surfactant could also affect soil adsorption capacity, but for desorption, there was no correlation.

Environmental behaviors of spirotetramat in water

Spirotetramat is a pesticide with bidirectional systemicity in both xylem and phloem. Currently, researches show that spirotetramat has definite toxicity to aquatic organism. This paper aims to study the environmental behaviors of spirotetramat in water, in the hope of providing guidance for security evaluation of spirotetramat. The researches in this paper showed that under lighting condition, the half-life period of spirotetramat in water was 13.59 days. In water, spirotetramat could be degraded into B-enol and B-keto. As seen from the residual concentrations of two products, B-enol was the dominant degradation product. Under different temperatures, the hydrolysis products of spirotetramat remain B-enol and B-keto. The temperature has little effect on the residual concentration of spirotetramat in water. The residual concentration of B-enol in water gradually increased with the extension of time but B-keto had no significant change. In the buffer solution of different pH values, the degradation rate of spirotetramat was significantly enhanced with the increase of solution pH value. The hydrolysis products of spirotetramat in buffer solution of different pH values were still B-enol and B-keto, and pH exerted certain influence on the residual concentration of B-enol in water. The hydrolysis conversion of spirotetramat has theoretical and practical significance for the safe and reasonable usage of it, as well as for the further evaluation of spirotetramat's ecological risk in water.

Cereal Cyst Nematodes: A Complex and Destructive Group of Heterodera Species

Small grain cereals have served as the basis for staple foods, beverages, and animal feed for thousands of years. Wheat, barley, oats, rye, triticale, rice, and others are rich in calories, proteins, carbohydrates, vitamins, and minerals. These cereals supply 20% of the calories consumed by people worldwide and are therefore a primary source of energy for humans and play a vital role in global food and nutrition security. Global production of small grains increased linearly from 1960 to 2005, and then began to decline. Further decline in production is projected to continue through 2050 while global demand for these grains is projected to increase by 1% per annum. Currently, wheat, barley, and oat production exceeds consumption in developed countries, while in developing countries the consumption rate is higher than production. An increasing demand for meat and livestock products is likely to compound the demand for cereals in developing countries. Current production levels and trends will not be sufficient to fulfill the projected global demand generated by increased populations. For wheat, global production will need to be increased by 60% to fulfill the estimated demand in 2050. Until recently, global wheat production increased mostly in response to development of improved cultivars and farming practices and technologies. Production is now limited by biotic and abiotic constraints, including diseases, nematodes, insect pests, weeds, and climate. Among these constraints, plant-parasitic nematodes alone are estimated to reduce production of all world crops by 10%. Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals. Heavily invaded young plants are stunted and their lower leaves are often chlorotic, forming pale green patches in the field. Mature plants are also stunted, have a reduced number of tillers, and the roots are shallow and have a "bushy-knotted" appearance. CCNs comprise a number of closely-related species and are found in most regions where cereals are produced.

Management of Root-knot Nematode (Meloidogyne incognita) on Pittosporum tobira Under Greenhouse, Field, and On-farm Conditions in Florida

Root-knot nematodes are important pests of cut foliage crops in Florida. Currently, effective nematicides for control of these nematodes on cut foliage crops are lacking. Hence, research was conducted at the University of Florida to identify pesticides or biopesticides that could be used to manage these nematodes. The research comprised on-farm, field, and greenhouse trials. Nematicide treatments evaluated include commercial formulations of spirotetramat, furfural, and Purpureocillium lilacinum (=Paecilomyces lilacinus) strain 251. Treatment applications were made during the spring and fall seasons according to manufacturer's specifications. Efficacy was evaluated based on J2/100 cm3 of soil, J2/g of root, and crop yield (kg/plot). Unlike spirotetramat, which did not demonstrate any measurable effects on Meloidogyne incognita J2 in the soil, furfural and P. lilacinum were marginally effective in reducing the population density of M. incognita on Pittosporum tobira. However, nematode reduction did not affect yield significantly. Although furfural and P. lilacinum have some potential for management of M. incognita on cut foliage crops, their use as a lone management option would likely not provide the needed level of control. Early treatment application following infestation provided greater J2 suppression compared to late application, suggesting the need for growers to avoid infested fields.

Resistance to Multiple Soil-Borne Pathogens of the Pacific Northwest, USA Is Colocated in a Wheat Recombinant Inbred Line Population

Soil-borne pathogens of the Pacific Northwest decrease yields in both spring and winter wheat. Pathogens of economic importance include Fusarium culmorum, Pratylenchus neglectus, P. thornei, and Rhizoctonia solani AG8. Few options are available to growers to manage these pathogens and reduce yield loss, therefore the focus for breeding programs is on developing resistant wheat cultivars. A recombinant inbred line population, LouAu (MP-7, NSL 511036), was developed to identify quantitative trait loci (QTL) associated with resistance to P. neglectus and P. thornei This same population was later suspected to be resistant to F. culmorum and R. solani AG8. This study confirms partial resistance to F. culmorum and R. solani AG8 is present in this population. Six major and 16 speculative QTL were identified across seven measured traits. Four of the six major QTL were found within the same genomic region of the 5A wheat chromosome suggesting shared gene(s) contribute to the resistance. These QTL will be useful in breeding programs looking to incorporate resistance to soil-borne pathogens in wheat cultivars.

Degradation kinetics and pathways of spirotetramat in different parts of spinach plant and in the soil

Spirotetramat is a new pesticide against a broad spectrum of sucking insects and exhibits a unique property with a two-way systemicity. In order to formulate a scientific rationale for a reasonable spray dose and the safe interval period of 22.4 % spirotetramat suspension concentrate on controlling vegetable pests, we analyzed degradation dynamics and pathways of spirotetramat in different parts of spinach plant (leaf, stalk, and root) and in the soil. We conducted experimental trials under field conditions and adopted a simple and reliable method (dispersive solid phase extraction) combined with liquid chromatography-triple quadrupole tandem mass spectrometry to evaluate the dissipation rates of spirotetramat residue and its metabolites. The results showed that the spirotetramat was degraded into different metabolite residues in different parts of spinach plant (leaf, stalk, and root) and in the soil. Specifically, spirotetramat was degraded into B-keto, B-glu, and B-enol in the leaf; B-glu and B-enol in the stalk; and only B-enol in the root. In the soil where the plants grew, spirotetramat followed a completely different pathway compared to the plant and degraded into B-keto and B-mono. Regardless of different degradation pathways, the dissipation dynamic equations of spirotetramat in different parts of spinach plant and in the soil were all based on the first-order reaction dynamic equations. This work provides guidelines for the safe use of spirotetramat in spinach fields, which would help prevent potential health threats to consumers.

Detection of Dual Heterodera avenae Resistance plus Tolerance Traits in Spring Wheat

The cereal cyst nematode Heterodera avenae reduces wheat yield in the Pacific Northwest. Resistance and tolerance traits among spring wheat cultivars were poorly defined. Screening trials were conducted with 39 cultivars over a 2-year period in irrigated commercial fields that were infested by H. avenae. Comparisons were made between drill strips treated or untreated with aldicarb at the time of planting. Root sampling at the time of plant anthesis indicated that cultivars differed greatly in susceptibility to H. avenae, with numbers of newly produced white H. avenae females ranging from <5 to 70 per plant. Aldicarb reduced mean numbers of white females as much as 99% on the most susceptible cultivar ('Glee') and increased mean grain yield as much as 77% for the least tolerant cultivar ('Cataldo'). Density of H. avenae eggs in untreated soil following harvest was significantly higher than the density in aldicarb-treated plots. Agronomically acceptable traits of resistance plus tolerance were identified in one cultivar of hard red spring wheat ('WB-Rockland') and two cultivars of hard white spring wheat ('Klasic' and 'LCS Star') but in none of the soft white spring wheat cultivars. This is the first report of spring wheat cultivars expressing the dual traits of resistance plus tolerance to H. avenae.

Spring Barley Resistance and Tolerance to the Cereal Cyst Nematode Heterodera avenae

Heterodera avenae is a cereal cyst nematode that reduces wheat yields in the Pacific Northwest of the United States. Barley is also susceptible but there were no previous reports of resistance or tolerance to H. avenae in the United States. Spring barley cultivars were assayed in H. avenae-infested fields over 2 years. Cultivars were planted in plots treated or not treated with aldicarb. Forty-five cultivars were evaluated for the market classes of two- and six-row feed barley cultivars and two- and six-row malt barley cultivars. One two-row feed barley ('Lenetah') was ranked as resistant and four were tolerant or very tolerant. In total, 1 two-row malt barley ('Odyssey') was very resistant and 10 were tolerant or very tolerant. Two six-row feed and two six-row malt barley cultivars were tolerant or very tolerant but none were resistant. Seven feed barley cultivars were ranked as having a balance of at least moderate resistance plus moderate tolerance: 'Champion', Lenetah, 'Xena', 'Idagold II', 'Transit', 'Millennium', and 'Goldeneye'. This is the first report of resistance and tolerance of barley in H. avenae-infested fields in the Pacific Northwest. Barley productivity can be improved by planting resistant plus tolerant cultivars or by using highly resistant and highly tolerant cultivars as parents in barley improvement programs.

Spirotetramat causes an arrest of nematode juvenile development

Spirotetramat (Movento™, Bayer CropScience) (SPT), an effective insecticide, has also demonstrated potential activity as a nematicide. No significant effects on hatching rates of Caenorhabditis elegans, Meloidogyne incognita or Heterodera glycines were observed when eggs were soaked in a maximum concentration of 105 ppm of technical grade spirotetramat-enol (SPT-enol), the active form in plants. Synchronised first-stage juveniles of C. elegans soaked in SPT-enol concentrations as low as 30 ppm demonstrated arrested juvenile development with calculated EC95 of 44-48 ppm. Single applications of formulated SPT (Movento 240SC) were applied to plant foliage at the labelled insecticidal rate of 87.6 g a.s. ha−1 at 1-week intervals on soybean plants inoculated with H. glycines or tomato plants inoculated with M. incognita in glasshouse tests. SPT consistently inhibited nematode development to reproductive maturity when applied at 1-2 weeks after inoculation. Optimal SPT application timings coincide with early stages of root infection, when nematodes are still in vulnerable juvenile stages.

Chemometric-assisted QuEChERS extraction method for the residual analysis of thiacloprid, spirotetramat and spirotetramat's four metabolites in pepper: Application of their dissipation patterns

Chemometric tools equipped with a Plackett-Burman (P-B) design, a central composite design (CCD) and a desirability profile were employed to optimise the QuEChERS (quick, easy, cheap, effective, rugged and safe) method for the quantification of thiacloprid, spirotetramat and spirotetramat's four metabolites in pepper. The average recoveries were in the range of 71.6-119.5%, with relative standard deviations ⩽ 12.1%. The limit of quantification for the method was less than 0.01 mg/kg. The method was applied to field samples to evaluate the residual characteristics of thiacloprid and spirotetramat. The data showed that the first+first-order model is a better fit than the first order model for the dissipation of thiacloprid and spirotetramat in pepper. The half-lives of thiacloprid and spirotetramat in pepper are 0.81 and 1.21 days, respectively. The final residues were between 0.016 mg/kg and 0.13 mg/kg for thiacloprid and 0.08 mg/kg and 0.12 mg/kg for spirotetramat.

Risk assessment of mixture formulation of spirotetramat and imidacloprid in chilli fruits

Persistence and risk assessment of spirotetramat and imidacloprid in chilli fruits were studied following three applications of a mixture formulation of spirotetramat (12%) and imidacloprid (12%) at 1000 and 2000 mL ha(-1). Residues of spirotetramat and imidacloprid in chilli were estimated by high-performance liquid chromatograph (HPLC). Residues of spirotetramat and imidacloprid dissipated to more than 65% after 3 days at both the dosages. Residues of spirotetramat on chilli fruits were found to be below its limit of quantification (LOQ) of 0.03 mg kg(-1) after 5 and 7 days for recommended and double the recommended dosages, respectively. Similarly, imidacloprid residues were found to be below its LOQ of 0.01 mg kg(-1) at 7 and 10 days, respectively. Half-life periods for spirotetramat were found to be 1.91 and 1.30 days, whereas, for imidacloprid, these values were observed to be 1.41 and 1.65 days at recommended and double the recommended dosages, respectively. Red chilli samples collected after 20 days of the last application did not show the presence of spirotetramat and imidacloprid at their respective determination limit. As the theoretical maximum residue contributions on chilli fruits are found to be less than the maximum permissible intake values on initial deposits, a waiting period of 1 day may follow to reduce risk before consumption at the recommended dose.

Species-Specific PCR Assays for Differentiating Heterodera filipjevi and H. avenae

Heterodera avenae and H. filipjevi are economically important cyst nematodes that restrict production of cereal crops in the Pacific Northwest United States and elsewhere in the world. Identification of these two species is critical for recommending and implementing effective management practices. Primers were designed from the internal transcribed spacer (ITS) regions of H. avenae and H. filipjevi ribosomal DNA. The primers were highly specific when examined on target isolates but did not amplify DNA from nontarget Heterodera, Globodera, Meloidogyne, Pratylenchus, and other nematode species tested. Polymerase chain reaction (PCR) and amplification conditions were established, and H. avenae and H. filipjevi were clearly distinguished by PCR fragments of 242 and 170 bp, respectively. Robust PCR amplification was achieved with DNA extracted from a single egg or second-stage juvenile (J2) using a laboratory-made worm lysis buffer, and DNA from 0.5 egg or J2 using a commercial kit. The PCR assays were successfully employed for differentiation of H. filipjevi and H. avenae populations collected from eight locations in three Pacific Northwest states. This is the first report of a species-specific ITS PCR assay to detect and identify H. filipjevi. The assays for both species will enhance diagnosis of cereal cyst nematode species in infested fields.

Spring Wheat Tolerance and Resistance to Heterodera avenae in the Pacific Northwest

The cereal cyst nematode Heterodera avenae reduces wheat yields in the Pacific Northwest. Previous evaluations of cultivar resistance had been in controlled environments. Cultivar tolerance had not been evaluated. Seven spring wheat trials were conducted in naturally infested fields in three states over 2 years. A split-plot design was used for all trials. Five trials evaluated both tolerance and resistance in 1.8-by-9-m plots treated or not treated with nematicides. Two trials evaluated resistance in 1-m head rows where each wheat entry was paired with an adjacent row of a susceptible cultivar. Cultivars with the Cre1 resistance gene ('Ouyen' and 'Chara') reduced the postharvest density of H. avenae under field conditions, confirming Cre1 parents as useful for germplasm development. Ouyen was resistant but it was also intolerant, producing significantly lower grain yield in controls than in plots treated with nematicides. Susceptible cultivars varied in tolerance. Undefined resistance was identified in one commercial cultivar ('WB-Rockland) and four breeding lines (UC1711, SO900163, SY-B041418, and SY-97621-05). This research was the first systematic field demonstration of potential benefits to be derived through development and deployment of cultivars with resistance plus tolerance to cereal cyst nematode in North America.

Influence of Nematicides and Fungicides on Spring Wheat in Fields Infested with Soilborne Pathogens

A complex of fungal soilborne pathogens and plant-parasitic nematodes reduces wheat yields in the Pacific Northwest. On several other crops in nematode-infested soils, seed treatment with abamectin (Avicta) or Bacillus firmus (Votivo) or foliar application of spirotetramat (Movento) reduced root injury and improved yield. These products, along with fungicide seed treatments and aldicarb (Temik), were evaluated in 13 spring wheat trials over 3 years. During 2011, the mean wheat yield at four locations was 419 kg/ha greater (valued at $122/ha) from seed treated with fungicides and insecticide than from untreated seed, due to protection against soilborne fungal pathogens. Aldicarb increased the mean grain yield over the fungicide-plus-insecticide treatment by another 798 kg/ha (valued at $254/ha) and also reduced the density of Heterodera avenae but is not registered for use on wheat. Abamectin and B. firmus had negligible effects on grain yield and postharvest density of Pratylenchus spp. and H. avenae. Spirotetramat reduced density of H. avenae but did not improve grain yield. We conclude that management of fungal pathogens by seed protectants remains essential and that management of nematodes can be achieved through crop rotations and genetic resistance.

A Fluidizing Column for Extracting Cysts of Heterodera avenae from Soil

The cereal cyst nematode Heterodera avenae can be extracted from soil using several different floatation or elutriation methods. Automated methods are prohibitively expensive for use in small labs and, for optimal efficiency, floatation methods require that the soil be air dried for an extended period. A method which suspends soil particles in a water column above a fluidizing plate was reported as being most efficient with wet and dry soils. Use of the fluidizing column for extracting H. avenae has not been reported in the United States and materials to construct the column using contemporary components have not been described. Objectives of this research were to construct a column with components available in the United States, and to compare numbers of cysts and eggs plus juveniles (from cysts) extracted by the column and three other floatation methods: Fenwick can, flask, and Cobb sieving. From a soil containing recently produced (more dense) cysts, the column extracted at least 18% more cysts and 23% more eggs plus juveniles than the Fenwick and flask methods. The fluidizing column was found to be useful for small laboratories because it is inexpensive ($253 for two columns), easily and quickly constructed by nonprofessional labor, and produces adequately repeatable results.