Herbicide Efficacy of Spot Spraying Systems in Fallow and Postharvest in the Pacific Northwest Dryland Wheat Production Region.

Real-time spot spraying technology has the potential to reduce herbicide costs and slow herbicide resistance. However, few studies exist on the efficacy of this technology in the Pacific Northwest (PNW). This research compared the herbicide efficacy (reduction in weed density and cover) of WEED-IT and WeedSeeker spot spraying systems to uniform spraying in fallow and postharvest in 2019 and 2020. Weed community types included naturally occurring weeds, natural + Russian thistle (Salsola tragus L.), or natural + kochia (Bassia scoparia (L.) A. J. Scott). Herbicides included glyphosate or the pre-mix bromoxynil + pyrasulfotole. Additionally, herbicide efficacy was studied with short stubble (~10 cm), tall stubble (~25 cm), and normal stubble (~20 cm) with chaff and straw removed. In fallow, herbicide efficacy was 1.5 times higher for uniform applications than for WEED-IT or WeedSeeker in 2019 and 2020. Herbicide efficacy was also 1.9 times higher for uniform applications in postharvest in 2019 but no differences were found in 2020. The weed community impacted herbicide efficacy but herbicide efficacy did not differ between residue management treatments. Finally, WEED-IT and WeedSeeker used 53% less herbicide volume in comparison to uniform applications. This research demonstrated that spot spraying technology can be efficacious and economical for growers in the PNW.

Weed responses to fallow management in Pacific Northwest dryland cropping systems.

A two-year rotation of summer fallow (SF)/winter wheat (WW) is the most common cropping system in low precipitation areas of the U.S. Pacific Northwest (PNW). In SF, multiple tillage operations are used to manage weeds and maximize soil water storage and potential WW yield. Reduced tillage fallow (RTF) is an alternative to SF that leaves >30% of the previous crop's residue on the surface. A four-year (2014-18) field study was conducted to evaluate the influence of SF and RTF on weed species density, cover and composition in dryland WW; determine if changes in these weed infestation attributes have any influence on crop density and yield; and evaluate economic costs of each type of fallow management. The experimental design was randomized complete block with four replications where each phase of SF/WW and RTF/WW rotations was present every year. Individual plots of WW were divided into a weedy sub-plot with no weed control, general area with chemical weed control, and weed-free sub-plot where weeds were manually removed. Infestations of annual grass and other weeds in weedy sub-plots increased throughout the study. Grass weed cover, consisting mainly of downy brome (Bromus tectorum L.), and total weed cover were significantly lower in WW following RTF than following SF in all years except 2018. Densities of grass and total weeds were similar in both fallow managements indicating that weed plants were larger in WW following SF than following RTF due to earlier or faster emergence. Grass cover differences were not found in general areas likely because of a reduced seedbank. When weeds were present, mean yield of WW was higher following RTF than SF indicating that weeds were less competitive in RTF. Reduced tillage fallow could improve weed management in fallow/WW cropping systems of the PNW compared to SF/WW, particularly if the most problematic species are grasses.

Identification of glyphosate resistance in Salsola tragus in north-eastern Oregon.

BACKGROUND: Farmers in the low-rainfall region of eastern Oregon rely on repeated applications of non-selective herbicides, predominately glyphosate, to control Salsola tragus in no-till fallow systems. Reports of poor glyphosate effectiveness have increased in recent years. Reduced efficacy is often attributed to dust, water stress, or generally poor growing conditions during application. Inadequate control also may be the result of the evolution of glyphosate resistance. Therefore, studies were undertaken to determine if glyphosate-resistant S. tragus populations occur in Oregon. RESULTS: Results from dose-response studies confirmed glyphosate resistance in three of 10 Oregon Salsola tragus populations. The ratio I50R /I50S from dose-response curves was, on average, 3.1 for the relative dry biomass per plant and 3.2 for the % of surviving plants per pot in these three populations. Plant mortality at recommended glyphosate doses for the resistant populations was less than 30% 3 weeks after treatment. CONCLUSIONS: Glyphosate resistance in S. tragus highlights the imperative need to diversify weed control strategies to preserve the longevity and sustainability of herbicides in semi-arid cropping systems of the Pacific Northwest. © 2017 Society of Chemical Industry.

Selected Pacific Northwest Crops as Hosts of Pratylenchus neglectus and P. thornei.

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 'Monida', chickpea 'Myles', and lentil 'Athena' and 'Morton'. Good hosts of P. neglectus but not of P. thornei included 10 Brassica spp. (5 canola, 2 mustard, and 3 camelina cultivars), chickpea 'Sierra', sudangrass 'Piper', and sorghum/sudangrass hybrid 'Greentreat Plus'. Good hosts of P. thornei but not of P. neglectus included lentil 'Skyline' and pea 'Granger', 'Journey', and 'Universal'. Poor or minor hosts of both Pratylenchus spp. included chickpea 'Dwelley', pea 'Badminton', safflower 'Gila', 'Girard', and 'KN 144', sunflower '2PD08', flax 'Pembina', eastern gamagrass 'Pete', and switchgrass 'Blackwell'. Results of these assays will provide guidance for improving crop rotation and cultivar selection efficiencies.

Selected Pacific Northwest Rangeland and Weed Plants as Hosts of Pratylenchus neglectus and P. thornei.

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 'Critana', smooth brome 'Manchar', seven wheatgrasses, and jointed goatgrass. Good hosts of P. neglectus but not P. thornei included two hairy vetches, western wheatgrass 'Rosana', big bluegrass 'Sherman', tall wheatgrass '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 'Durar', sheep fescue '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.

Resistance and Tolerance of Landrace Wheat in Fields Infested with Pratylenchus neglectus and P. thornei.

Pratylenchus neglectus and P. thornei reduce wheat yields in the Pacific Northwest of the United States. Resistant landrace cultivars have been identified using controlled environments. Field resistance and tolerance characteristics were compared over 3 years and two locations for four spring wheat cultivars: the susceptible '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 preplant and postharvest 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 3 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.

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 Semiarid Cropping Systems on Root Diseases and Inoculum Density of Soilborne Pathogens.

There is interest in converting the 2-year rotation of rainfed winter wheat with cultivated fallow in the Pacific Northwest of the United States into direct-seed (no-till) systems that include chemical fallow, spring cereals, and food-legume and brassica crops. Eight cropping systems in a low-precipitation region (<330 mm) were compared over 9 years to determine effects of changes on diseases. Fusarium crown rot was more prevalent in wheat following cultivated than chemical fallow, and Rhizoctonia root rot was more severe when winter wheat was rotated with chemical fallow than with no-till winter pea. Take-all occurred even during the driest years and was more severe on annual spring wheat than on annual spring barley. Inoculum density (picograms of DNA per gram of soil) differed (α < 0.05) among cropping systems for Fusarium culmorum, F. pseudograminearum, Gaeumannomyces graminis var. tritici, and Pythium spp. but not for Rhizoctonia solani AG-8. Phoma medicaginis var. pinodella was detected only where winter pea was planted frequently. This is the first report of P. medicaginis as a component of the dryland stem rot complex of pea in north-central Oregon. Results of this investigation will provide guidance for developing crop species with resistance to Fusarium crown rot and black stem of pea.

Effects of Crop Rotations and Tillage on Pratylenchus spp. in the Semiarid Pacific Northwest United States.

There is interest in converting rainfed cropping systems in the Pacific Northwest from a 2-year rotation of winter wheat and cultivated fallow to direct-seed (no-till) systems that include chemical fallow, spring cereals, and food legume and brassica crops. Little information is available regarding effects of these changes on plant-parasitic nematodes. Eight cropping systems in a low-precipitation region (<330 mm) were compared over 9 years. Each phase of each rotation occurred each year. The density of Pratylenchus spp. was greater in cultivated than chemical fallow, became greater with increasing frequency of host crops, and was inversely associated with precipitation (R2 = 0.92, α < 0.01). Densities after harvesting mustard, spring wheat, winter wheat, and winter pea were greater (α < 0.01) than after harvesting spring barley or spring pea. Camelina also produced low densities. Winter wheat led to a greater density of Pratylenchus neglectus and spring wheat led to a greater density of P. thornei. Density of Pratylenchus spp. was correlated (R2 = 0.88, α < 0.01) but generally higher when detected by real-time polymerase chain reaction on DNA extracts from soil than when detected by a traditional method. Selection of different Pratylenchus spp. by different wheat cultivars or growth habit must be addressed to minimize the level of nematode risk to future plantings of intolerant crops.

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.

Geocenamus brevidens Associated with Reduced Yield of No-Till Annual Spring Wheat in Oregon.

Associations between stunt nematodes and yield of no-till annual spring wheat (Triticum aestivum) 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.

Pratylenchus thornei Associated with Reduced Wheat Yield in Oregon.

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.

Plant-Parasitic Nematodes Associated with Reduced Wheat Yield in Oregon: Heterodera avenae.

Heterodera avenae is widely distributed in the western United States, where most wheat is grown in non-irrigated winter wheat/summer fallow rotations in low rainfall regions. Economic and social pressures have motivated growers to pursue a transition from winter wheat/summer fallow rotation to no-till annual spring cereals. Annual cereals are also planted in some irrigated fields. The impact of H. avenae on spring wheat yield in the Pacific Northwest had been observed but not quantified. Spring wheat was planted with or without aldicarb to examine relationships between H. avenae and yield under dryland and irrigated conditions in moderately infested fields. Spring wheat yields were negatively correlated (P < 0.05) with initial populations of H. avenae. Aldicarb application improved spring wheat yield as much as 24%. The infective juvenile stage of H. avenae reached a peak density during mid-spring. Yield of irrigated annual winter wheat was also negatively correlated with initial density of H. avenae. Research priorities necessary to develop control strategies include a description of the pathotype, identification of sources for genetic resistance, and integrated practices designed to manage multiple yield-reducing pests.

Pathogenicity of Fungi Associated with the Wheat Crown Rot Complex in Oregon and Washington.

Crown rot of wheat in the Pacific Northwest is caused by a complex including Bipolaris sorokiniana, Fusarium avenaceum, F. culmorum, F. pseudograminearum, and Microdochium nivale. Relative pathogenicity was examined under greenhouse conditions for 178 isolates of the five species, and under field conditions for 24 isolates of B. sorokiniana, F. culmorum, and F. pseudograminearum. In the greenhouse, all five species reduced (P < 0.05) plant height relative to noninoculated controls. Disease severity was inversely correlated with plant height for the three Fusarium spp. In one or more of four experiments with spring wheat in the field, all three species reduced stand establishment and density of mature heads and increased the incidence and severity of crown rot. F. culmorum and F. pseudograminearum caused the greatest disease severity and plant damage and were the only pathogens that reduced grain yield. Virulence ratings were variable among isolates for each species in all greenhouse and field experiments. Isolate variability was especially high for the location and year variables in field experiments. Mixtures of multiple isolates are required for future research.

Suppression of Wheat Growth and Yield by Pratylenchus neglectus in the Pacific Northwest.

Many wheat (Triticum aestivum) fields planted annually in the Pacific Northwest are infested by high populations 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. tritici. Intolerant cultivars had lower yields than Krichauff in rainfed but not in irrigated experiments. Density of P. neglectus in mature roots was generally lower for moderately resistant Krichauff than for susceptible Machete and Spear. Aldicarb improved yields in irrigated but not in rainfed experiments, and 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 to P. neglectus is suggested.

Crop Damage Estimates for Crown Rot of Wheat and Barley in the Pacific Northwest.

Crown rot of wheat and barley in the Pacific Northwest is caused by a complex of Fusarium pseudograminearum, F. culmorum, F. avenaceum, Bipolaris sorokiniana, and Microdochium nivale. Yield-loss estimates were made by evaluating yield components on tillers collected from commercial fields and sorted by disease severity classes, and by comparing yields for field plots inoculated with F. pseudograminearum with yields in naturally infested soil. Increasing crown rot severity caused an increase in grain protein content and reduction in grain yield, kernels per head, kernel weight, test weight, tiller height, and straw weight. Crown rot reduced winter wheat yield as much as 1,550 kg/ha (35%, $219/ha) in commercial fields, with a 13-field mean of 9.5% ($51/ha). Inoculation reduced yields as much as 2,630 kg/ha (61%, $372/ha) over that caused by the native pathogen flora. Rain-induced crusting of the soil surface greatly amplified preemergence damping-off caused by F. pseudograminearum. Crown rot caused the greatest losses during seasons of lowest precipitation but also damaged crops under wet conditions. Aboveground symptoms were not always apparent under conditions of moderate infection and yield constraint. Damage from crown rot in the Pacific Northwest is more widespread and damaging than previously recognized.

Economic impact of Hessian fly (Diptera: Cecidomyiidae) on spring wheat in Oregon and additive yield losses with Fusarium crown rot and lesion nematode.

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 nematode, Pratylenchus neglectus (Rensch, 1924) (Filipjev Schuurmanns & Stekhoven, 1941) and Pratylenchus 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 dollar 112 to dollar 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 seems to be the first quantitative yield loss estimate for Hessian fly in spring wheat in the semiarid environment of the inland Pacific Northwest.

Nematodes in dryland field crops in the semiarid pacific northwest United States.

Soils and roots of field crops in low-rainfall regions of the Pacific Northwest were surveyed for populations of plantparasitic 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 (r(2) = 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.