Abstracts of Papers Relating to Root-lesion and Stunt Nematodes

Thompson, A.L., R.W. Smiley, T.C. Paulitz, and K. Garland-Campbell. 2016. Identification of resistance to Pratylenchus neglectus and Pratylenchus thornei in Iranian landrace accessions of wheat. Crop Science 56:654-672.

 Wheat (Triticum aestivum) landrace accessions collected from 12 provinces in Iran were used to identify novel sources of resistance to Pratylenchus sp. and characterize important agronomic traits.  Seventy-eight accessions were assayed for dual-resistance to parasitic nematodes Pratylenchus neglectus and P. thornei in controlled environment assays.  Field trials conducted in Pullman, WA evaluated stripe rust (Puccinia striiformis f. sp. tritici) resistance under natural infection and the agronomic traits days to heading, grain volume weight, plant height, seed protein content, seed kernel characterization, glume tenacity, and pubescence.  Simple sequence repeat, SNP, and known vernalization markers were screened to assess the genetic diversity in the 78 accession subset.  Hierarchical cluster analysis was used to identify relatedness among accessions with the recorded genotypes.  Thirty-two accessions were identified as resistant and/or moderately resistant to both Pratylenchus species.  Three of these accessions also had moderate adult plant resistance to stripe rust in the field.  The range of plant height from two locations was 53-105 cm, days to heading post-planting was 46-84 days, and grain volume weight 151-728 kg/m-3.  The genetic cluster analysis identified five clusters based on the number of rare polymorphisms in the subset.  This data indicates there is a great deal of diversity within this subset that could be useful for wheat breeders to integrate genetic variation and resistance to Pratylenchus spp.

Thompson, A.L., R.W. Smiley, and K. Garland-Campbell. 2015. Registration of the LouAu (Louise/IWA8608077) wheat recombinant inbred line mapping population. Journal of Plant Registrations 9:424–429.

LouAu (Louise/IWA8608077) (MP-7, NSL 511036) is a wheat (Triticum aestivum L.) recombinant inbred line population developed by the USDA-ARS, with Oregon State and Washington State Universities, from a cross between the soft white spring cultivar Louise and the white facultative Iranian landrace IWA8608077. The population was developed by single seed descent from the F2 generation to the F5 generation. The population has 150 F2:5 recombinant inbred lines and has been used to study the genetics of resistance to root-lesion nematodes (Pratylenchus neglectus and P. thornei), and root architecture. The 26 linkage groups identified include 30 codominant simple sequence repeat markers and 2008 single nucleotide polymorphic markers from the Illumina 9K wheat single nucleotide polymorphism chip. Chisquare analysis shows 21 to 95% of identified polymorphic markers within individual linkage groups were in segregation distortion. The population frequency distributions have a normal distribution for the measured traits P. neglectus resistance, root length, root weight, root lignin content, and plant height. The population frequency distribution has a bimodal distribution for P. thornei resistance, left skewed for lateral root number and right skewed for growth stage. This population has shown potential for mapping resistance to other soilborne pathogens as well as abiotic stresses and will be useful in that endeavor.

Smiley, R. W., Yan, G. P., and Gourlie, J. A. 2014. Selected Pacific Northwest crops as hosts of Pratylenchus neglectus and P. thornei. Plant Disease 98:1341-1348.

Thirty crop species and cultivars were assayed in the greenhouse for efficiency as hosts of Pratylenchus neglectus and P. thornei. Hosting ability ratings were assigned using the ratio of final versus initial nematode density and also by comparing the final nematode density to that of a susceptible wheat control. Good hosts of both Pratylenchus spp. included oat cv. Monida, chickpea cv. Myles, and lentil cvs. Athena and Morton. Good hosts of P. neglectus but not P. thornei included 10 Brassica spp. (5 canola, 2 mustard, and 3 camelina cultivars), chickpea cv. Sierra, sudangrass cv. Piper, and sorghum/sudangrass hybrid cv. Greentreat Plus. Good hosts of P. thornei but not P. neglectus included lentil cv. Skyline, and pea cvs. Granger, Journey and Universal. Poor or minor hosts of both Pratylenchus spp. included chickpea cv. Dwelley, pea cv. Badminton, safflower cvs. Gila, Girard and KN 144, sunflower cv. 2PD08, flax cv. Pembina, eastern gamagrass cv. Pete, and switchgrass cv. Blackwell. Results of these assays will provide guidance for improving crop rotation and cultivar selection efficiencies.

Smiley, R. W., Yan, G. P., and Gourlie, J. A. 2014. Selected Pacific Northwest rangeland and weed plants as hosts of Pratylenchus neglectus and P. thornei. Plant Disease 98:1333-1340.

Eighteen rangeland plants and 16 weed species were assayed in the greenhouse for efficiency as hosts of Pratylenchus neglectus and P. thornei. Hosting ability ratings were assigned using the ratio of final versus initial nematode density and by comparing the final nematode density to that of susceptible wheat controls. Good hosts of both Pratylenchus spp. included thickspike bluegrass cv. Critana, smooth brome cv. Manchar, seven wheatgrasses, and jointed goatgrass. Good hosts of P. neglectus but not P. thornei included two hairy vetches, western wheatgrass cv. Rosana, big bluegrass cv. Sherman, tall wheatgrass cv. Alkar, green foxtail, kochia, large crabgrass, Palmer amaranth, redroot pigweed, tumble mustard, and wild oat. Good hosts of P. thornei but not P. neglectus included hard fescue cv. Durar, sheep fescue cv. Blacksheep, downy brome, and rattail fescue. Poor or minor hosts of both Pratylenchus spp. included two alfalfas, dandelion, horseweed, lambsquarters, prostrate spurge and Russian thistle. These assays will provide guidance for transitioning rangeland into crop production and for understanding the role of weeds on densities of Pratylenchus spp. in wheat-production systems.

Smiley, R.W., J. A. Gourlie, G.P. Yan, and K.E.L. Rhinhart. 2014. Resistance and tolerance of landrace wheat in fields infested with Pratylenchus neglectus and P. thornei. Plant Disease 98:797-805.

Pratylenchus neglectus and P. thornei reduce wheat yields in the Pacific Northwest USA. Resistant landrace cultivars have been identified using controlled environments. Field resistance and tolerance characteristics were compared over three years and two locations for four spring wheat cultivars; the susceptible cultivars Alpowa and Louise, and the resistant landraces AUS28451 and Persia 20. Proportions and densities of P. neglectus and P. thornei differed across seasons and locations. Resistance was evaluated by comparing pre-plant and post-harvest densities of nematodes in soil. Tolerance was evaluated by comparing grain yield and grain quality in plots treated or untreated by the nematicide aldicarb. Alpowa was susceptible and intolerant, Louise was susceptible and moderately tolerant, AUS28451 was resistant and intolerant, and Persia 20 was moderately susceptible and moderately intolerant. The species dominance shifted from P. neglectus to P. thornei in one field over a period of three years in apparent response to cultivars and crops planted. Estimates of economic loss caused by Pratylenchus spp. ranged from $8 to $20/ha. Economic benefits appear to be achievable by developing a spring wheat genotype with tolerance plus resistance, such as with a cross between AUS28451 and Louise.

Hajihassani, A., R.W. Smiley, and F.J. Afshar. 2013. Effects of co-inoculations with Pratylenchus thornei and Fusarium culmorum on growth and yield of winter wheat. Plant Disease 97:1470-1477.

Growth and yield of winter wheat are suppressed by Pratylenchus thornei and by Fusarium culmorum. Many fields in cereal production regions throughout the world are infested by both pathogens. We evaluated effects of one or both pathogens on winter wheat growth, grain yield, and disease parameters at heading and harvest stages over two years in inoculated, rainfed pots incubated outdoors. Nematodes were inoculated at 1, 2, or 4 P. thornei/g of soil and F. culmorum was added at 0.65 g of colonized millet seed/kg of soil. At harvest, compared to the non-inoculated control, the high rate of P. thornei reduced (P < 0.05) plant height, shoot weight, root weight and grain yield by 19%, 17%, 48%, and 31%, respectively. F. culmorum alone reduced these parameters by 15%, 16%, 22%, and 22%. Co-inoculations caused reductions of 27%, 38%, 61%, and 63%. The reproductive rate or P. thornei was not greatly affected by co-inoculation with F. culmorum. Disease severity ratings at both plant growth stages became amplified as the nematode density was increased, and were much greater in the presence of both pathogens. Effects of co-inoculation on grain yield were slightly greater than predicted by additive effects of the individual pathogens, suggesting a synergistic effect on yield depression. 

Yan, G.P., Smiley, R.W., Okubara, P.A., Skantar, A.M., and Reardon, C.L. 2013. Developing a realtime PCR assay for detection and quantification of Pratylenchus neglectus in soil. Plant Disease 97:757-764.

Pratylenchus neglectus is one of the most widespread and economically important nematodes that invade plant roots and restrict wheat productivity in the Pacific Northwest. It is challenging to quantify P. neglectus using microscopic methods for studies that require large scale sampling, such as assessment of rotation crops, wheat cultivars, and other management practices. A quantitative realtime polymerase chain reaction (qPCR) assay was developed to detect and quantify P. neglectus from DNA extracts of soil. The primers, designed from internal transcribed spacer region of rDNA, showed high specificity with a single melt curve peak to DNA from eight isolates of P. neglectus, but did not amplify DNA from 28 isolates of other plant parasitic and nonplant parasitic nematodes. A standard curve was generated from artificially infested soil showing a significant negative correlation (R2 = 0.96) between cycle threshold and log value of nematode numbers. The soil standard curve was validated using sterilized soil inoculated with lower numbers of P. neglectus. A significant positive correlation (R2 = 0.66) was observed for nematode numbers quantified from fifteen field soils using qPCR and the Whitehead tray and microscopic method. Realtime PCR provides a useful platform for efficient detection and quantification of P. neglectus directly from field soils.

Smiley, R. W., Machado, S., Gourlie, J. A., Pritchett, L. C., Yan, G. P., and Jacobsen, E. E. 2013. Effects of crop rotation and tillage on Pratylenchus species in the semi-arid Pacific Northwest. Plant Disease 97:537-546.

Rainfed cropping systems in the Pacific Northwest are slowly changing from a 2-year rotation of winter wheat and cultivated fallow to direct-seed (no-till) systems that include chemical fallow, spring cereals, and pulse and brassica crops. Little information is available regarding effects of these changes on diseases. Eight cropping systems were compared over nine years. Each phase of each rotation occurred each year. The density of Pratylenchus neglectus and P. thornei was greater in cultivated than chemical fallow, became greater with increasing frequency of host crops, and was inversely associated with rainfall (R2 = 0.92, α < 0.01). Highest densities occurred following mustard, spring wheat, winter wheat and winter pea. Lowest densities occurred following camelina, spring barley and spring pea. Winter wheat led to a greater density of P. neglectus and spring wheat and winter pea led to a greater density of P. thornei. Density of Pratylenchus sp. was correlated (R2 = 0.88, α < 0.01) but generally higher when detected by real-time PCR on DNA extracts from soil than when detected by a traditional method. Selection of different Pratylenchus species by different wheat cultivars or growth habit must be addressed to minimize the level of nematode risk to future plantings of intolerant crops.

Kandel, S.L., R.W. Smiley, K.. Garland-Campbell, A.A. Elling, J. Abatzoglou, D. Huggins, R. Rupp, and T.C. Paulitz. 2013. Relationship between climatic factors and distribution of Pratylenchus spp. in the dryland wheat-production areas of eastern Washington. Plant Disease 97:1448-1456.

Field surveys were conducted by collecting soil samples to estimate nematode densities in soil from winter wheat, spring wheat, spring barley, and spring legumes (lentil, chickpea, and pea) fields during 2010 and 2011. Pratylenchus spp. were observed in 60% of sampled fields. However, nematodes were detected in nearly all of the survey fields in high numbers where crops were grown every year. To identify climatic variables associated with density of Pratylenchus spp. in soil, correlation and regression analyses were performed using climate data of survey sites from 1979 to 2010. Fifty-seven climate variables were significantly correlated with densities of Pratylenchus spp. All precipitation variables were significantly positively correlated with nematode abundance. Summer maximum air temperature was negatively correlated and winter minimum air temperature was positively correlated with nematode densities. In addition, both years’ nematode densities were significantly correlated with cropping intensity. Five multivariate regression models for 2010 and seven models for 2011 nematode abundance levels were developed. The majority of the climate variables selected in the models were related to precipitation. Knowledge of root-lesion nematode distribution in the dryland region of eastern Washington and associated climate variables may be helpful to determine risk and apply management practices to minimize crop damage.

Yan, G. P., Smiley, R. W., and Okubara, P. A. 2011. Detection and quantification of Pratylenchus thornei in DNA extracted from soil using real-time PCR. Phytopathology 102:14-22.

 The root-lesion nematode Pratylenchus thornei is one of the most important pests restricting productivity of wheat in the Pacific Northwest (PNW). It is laborious and difficult to use microscopy to count and identify the nematodes in soils. A SYBR Green I-based real-time polymerase chain reaction (PCR) assay was developed to detect and quantify this species from DNA extracts of soil. A primer set, designed from the internal transcribed spacer region (ITS1) of rDNA, was highly specific to P. thornei and did not amplify DNA from 27 isolates of other Pratylenchus species, other nematodes and six fungal species present in PNW wheat fields. A standard curve relating threshold cycle (Ct) and log values of nematode number was generated from artificially infested soils. The standard curve was supported by a high correlation between the numbers of P. thornei added to soil and the numbers quantified using real-time PCR. Examination of 15 PNW dryland field soils and 20 greenhouse samples revealed significant positive correlations between the numbers determined by real-time PCR and by the Whitehead tray and microscopic method. Real-time PCR is a rapid, sensitive alternative to time-consuming nematode extractions, microscopic identification, and counting of P. thornei from field and greenhouse soils.

Smiley, R.W., and Machado, S. 2009. Pratylenchus neglectus reduces yield of winter wheat in dryland cropping systems. Plant Disease 93:263-271.

 Wheat in low-precipitation regions of eastern Oregon and Washington is grown mostly as rainfed biennial winter wheat (10-month growing season) planted into cultivated fallow (14-month crop-free period). There are increasing trends for cultivated fallow to be replaced by chemical fallow and for spring cereals to be planted annually without tillage. Most fields are infested by the root-lesion nematodes Pratylenchus neglectus and/or P. thornei. A replicated multiyear experiment was conducted to compare cropping systems on soil infested by P. neglectus. Populations became greater with increasing frequency of the host crops mustard, pea and wheat. Annual winter wheat had the highest P. neglectus populations, the lowest capacity to extract soil water, and a lower grain yield compared to wheat grown biennially or rotated with other crops. Populations of P. neglectus did not differ for cultivated versus chemical fallow. Lowest populations occurred in annual spring barley. Winter wheat yield was inversely correlated with the population of P. neglectus. Measures to monitor and to reduce the population of P. neglectus in Pacific Northwest wheat fields are recommended.


Smiley, R.W. 2009. Root-lesion nematodes reduce yield of intolerant wheat and barley. Agronomy Journal 101:1322-1335.

Root-lesion nematodes (Pratylenchus neglectus and P. thornei) are widely distributed and substantially reduce grain yields in wheat-producing regions of the Pacific Northwest. The objective of this research was to determine if wheat and barley cultivars differ in tolerance to these nematode species. Field experiments were conducted by comparing yields in untreated and nematicide-treated plots over three years at two locations infested with either P. neglectus or P. thornei. Yield improvements from nematicide application ranged from 9% to 40% for spring cereals and 6% to 17% for winter cereals. Phenotypic tolerance responses differed (P < 0.01) among 45 cultivars of spring cereals but not among 22 and 45 cultivars of winter cereals. Tolerance ratings were assigned to spring cereals. This is the first report of wheat and barley tolerances to root-lesion nematodes in North America. Variability within data sets was used to estimate that 40 and 56 comparisons (experiments × replications) would be required to assign tolerance ratings at the 95% confidence interval for spring and winter cereals, respectively. Cultivar reactions in these tests, production and economic statistics for Idaho, Oregon, and Washington, and surveys of Pratylenchus in these states were used to estimate that P. neglectus and P. thornei reduce region-wide yields as much as 5% annually, equaling 361 Gg (361,000 metric tons) valued at $51 million. It was concluded that this yield-based screening procedure was impractical for routine screening but added emphasis to the importance of these root parasites in regions with low precipitation.

Smiley, R.W., J.G. Sheedy, and S.A. Easley. 2008. Vertical distribution of Pratylenchus spp. in silt loam soil of Pacific Northwest dryland crops. Plant Dis. 92:1662-1668. 

Dryland field crops in the Pacific Northwest USA are commonly produced in soil infested by the root-lesion nematodes Pratylenchus neglectus and P. thornei. Soils were sampled from 0 to 120 cm depth to examine the vertical distribution of these Pratylenchus spp. in Oregon. Both species were found through entire soil profiles of all cropping systems. High populations were measured in annually cropped fields (>14,500/kg of soil) and in winter wheat-summer fallow rotations (>12,500/kg of soil). Greatest populations generally occurred in the surface 30 cm of annually cropped fields and at 15 to 60 cm in winter wheat-summer fallow rotations. Rotation with barley significantly reduced Pratylenchus spp. populations. Sampling to 90 cm depth was required to detect more than 90% of the population in each soil profile. Soil samples should be collected to 30 to 45 cm depth to accurately estimate populations of Pratylenchus spp. in dryland crops in the Pacific Northwest.

Yan, G.P., R.W. Smiley, P.A. Okubara, A. Skantar, S.A. Easley, J.G. Sheedy, and A.L. Thompson. 2008. Detection and discrimination of Pratylenchus neglectus and P. thornei in DNA extracts from soil. Plant Disease 92:1480-1487.

A species-specific polymerase chain reaction (PCR) method was developed to detect and identify the root-lesion nematodes Pratylenchus neglectus and P. thornei in soil. A primer set was designed from Pratylenchus 26S rRNA gene sequences of the D3 expansion domain and their specificity was confirmed with plant-parasitic and non-parasitic nematodes typically present in the soil communities, and with six fungal species commonly associated with wheat root rot. DNA obtained using a commercially available kit and an inexpensive method developed in our laboratory gave comparable amplification. Optimized PCR conditions were established and the two species were differentiated by PCR products of 144 bp for P. neglectus and 288 bp for P. thornei. With this assay we were able to detect a single juvenile in 1 g of sterilized, inoculated soil. Examination of 30 field soil samples revealed that this method was applicable to a range of soils naturally infested with these two pathogens in Oregon. This new PCR-based method is rapid, efficient, and reliable, does not require expertise in nematode taxonomy compared to commonly used nematode-extraction and morphological identification techniques, and can be used as a rapid diagnostic tool in commercial and research applications for disease forecast and management.

Smiley, R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2006. Geocenamus brevidens reduces yield of no-till annual spring wheat in Oregon. Plant Dis. 90:885-890.

Associations between stunt nematodes and yield of no-till annual spring wheat were examined at two eastern Oregon locations. Geocenamus brevidens was the only species detected at one location and was mixed with Tylenchorhynchus clarus at another location. Six cultivars were planted with or without application of aldicarb during 2001. Inverse correlations between yield and stunt nematode density were significant at the G. brevidens-only site (P = 0.04) but not the G. brevidens + T. clarus site (P = 0.44). Yields were inversely correlated (P < 0.01) with stunt nematode populations at both sites during 2002. Aldicarb improved grain yields at both locations during 2001 (17% and 24%, P < 0.01) but not at the single location treated with aldicarb during 2002 (10%, P = 0.06). A lack of association between yield and T. clarus in 19 previously unreported experiments is discussed. Reduced wheat yield in response to stunt nematodes in Oregon is likely due to parasitism by G. brevidens and not T. clarus. This is the first report associating G. brevidens with suppression of wheat yield in the Pacific Northwest. Further studies are needed to define cropping systems and locations where G. brevidens may cause economic damage.

Smiley, R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2005. Pratylenchus thornei associated with reduced wheat yield in Oregon. Journal of Nematology 37:45-54.

Pratylenchus thornei reaches high population densities in non-irrigated annual cropping systems in low-rainfall regions of the Pacific Northwest. Two spring wheat varieties with different levels of tolerance and susceptibility to P. thornei were treated or not treated with aldicarb in three experiments. Grain yield was inversely correlated (P< 0.05) with pre-plant populations of P. thornei in soil and with P. thornei density in mature roots. As population of P. thornei increased, yield of the moderately tolerant/moderately susceptible variety Krichauff was generally more stable than for the intolerant/susceptible variety Machete. The reproductive factor (Pf/Pi) was generally lower (P < 0.05) for Krichauff than Machete. Aldicarb improved wheat yield (P < 0.05) in highly infested fields by an average of 67% for Krichauff and 113% for Machete. Aldicarb increased (P < 0.05) numbers of headed tillers, plant height, and grain test weight and kernel weight, and reduced (P < 0.05) the density of P. thornei in mature wheat roots, variability in height of heads, and leaf canopy temperature. Aldicarb did not improve yield in a soil with a low population of P. thornei. This is the first report that P. thornei causes economic damage to wheat in the Pacific Northwest.

Smiley, R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2005. Suppression of wheat growth and yield by Pratylenchus neglectus in the Pacific Northwest. Plant Disease 89: 958-968.

Many wheat fields planted annually in the Pacific Northwest are infested by high numbers of the lesion nematode, Pratylenchus neglectus. Spring wheat cultivars varying in tolerance and resistance to P. neglectus were treated or not treated with aldicarb to examine relationships between the nematode and growth and yield of annual direct-seeded (no-till) wheat. Increasing initial density of P. neglectus in soil was more strongly associated with declining growth and yield of intolerant (Machete and Spear) than moderately tolerant (Frame and Krichauff) cultivars. Yield suppression by P. neglectus was generally 8 to 36% for intolerant cultivars, but reached 71% in soil also harboring Heterodera avenae, Rhizoctonia solani AG-8, and Gaeumannomyces graminis var. graminis. Intolerant cultivars had lower yields than Krichauff in rainfed but not irrigated experiments. Density of P. neglectus in mature roots was lower for moderately resistant Krichauff than susceptible Machete and Spear in two experiments. Aldicarb improved yields in irrigated but not rainfed experiments, and generally increased plant height and reduced variability in tiller height, canopy temperature, and density of P. neglectus in roots. This is the first report of damage to wheat by P. neglectus in the Pacific Northwest. Breeding wheat for tolerance and resistance is suggested.

Smiley, R.W., K. Merrifield, L.-M. Patterson, R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2004. Nematodes in dryland field crops in the semiarid Pacific Northwest USA.  Journal of Nematology 36:54-68.

Soils and roots of field crops in low-rainfall regions of the Pacific Northwest were surveyed for populations of plant-parasitic and non-plant-parasitic nematodes. Lesion nematodes (Pratylenchus species) were recovered from 123 of 130 non-irrigated and 18 of 18 irrigated fields. Pratylenchus neglectus was more prevalent than P. thornei but mixed populations were common. Population densities in soil were affected by crop frequency and rotation but not by tillage or soil type (P<0.05). Many fields (25%) cropped more frequently than 2 of 4 years had potentially damaging populations of lesion nematodes. Pratylenchus neglectus density in winter wheat roots was inversely correlated with grain yield (R2 = 0.64, P = 0.002), providing the first field-derived evidence that Pratylenchus is economically important in Pacific Northwest dryland field crops. Stunt nematodes (Tylenchorhynchus clarus and Geocenamus brevidens) were detected in 35% of fields and were occasionally present in high numbers. Few fields were infested with pin (Paratylenchus species) and root-knot (Meloidogyne naasi and M. chitwoodi) nematodes. Nematodes detected previously, but not during this survey included cereal cyst (Heterodera avenae), dagger (Xiphinema species), and root-gall (Subanguina radicicola) nematodes.

Smiley, R.W., J.A. Gourlie, R.G. Whittaker, S.A. Easley, and K.K. Kidwell. 2004. Economic impact of Hessian fly (Diptera: Cecidomyiidae) on spring wheat in Oregon and additive yield losses with Fusarium crown rot and lesion nematode. Journal of Economic Entomology 97:397-408.

Damage caused by Hessian fly, Mayetiola destructor (Say), was quantified in spring wheat, Triticum aestivum L., trials near Pendleton and Moro, OR, during 2001 and 2002. Five field experiments were established to examine genetic resistance to Fusarium crown rot, Fusarium pseudograminearum (O'Donnell & Aoki), and economic damage by lesion nematodes, Pratylenchus neglectus ((Rensch, 1924) Filipjev Schuurmanns & Stekhoven, 1941) and P. thornei (Sher & Allen, 1941). Hessian fly became the dominant factor affecting grain yield in four experiments. Genotypes carrying the H3-resistance gene had grain yields 66% and 68% higher than susceptible genotypes in cultivar trials during 2001 and 2002, respectively. Yield reductions were detected when Hessian fly infestation rates exceeded 50% plants during 2001 and 15% plants (8% tillers) during 2002. In two trials during 2001, in-furrow application of aldicarb (Temik) at planting improved yields of four Hessian fly-susceptible cultivars by 72% and 144% (up to 1,959 kg/ha) and yields of one Hessian fly-resistant cultivar by 2% and 3%. Resistant cultivars and aldicarb improved grain quality as much as two market grades during 2001. The value of increased grain production with Hessian fly-resistant cultivars in four field experiments ranged from $112 to $252/ha, excluding price incentives for improved market quality. Yield reduction due to combined damage from Hessian fly and either Fusarium crown rot or lesion nematode was additive. This report seams to be the first quantitative yield loss estimate for Hessian fly in spring wheat in the semiarid environment of the inland Pacific Northwest.
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