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The benefits of no-till fallow, which include reduced soil erosion, improved soil health, and increased stored soil water, are in jeopardy because of the widespread development of glyphosate resistance in Russian thistle. The objective of this research was to evaluate the efficacy of soil-active, residual herbicides for Russian thistle control in no-till fallow. The combinations of sulfentrazone + carfentrazone and flumioxazin + pyroxasulfone, and metribuzin alone were each applied in late fall, late winter, and split-applied in late fall and late winter at three sites: Adams, OR, in 2017–2018; Lind, WA, in 2018–2019; and Ralston, WA, in 2019–2020. All treatments provided good to excellent control of the initial flush of Russian thistle when assessed in mid-May, except the late-fall application of metribuzin at all three sites, and the late-fall application of sulfentrazone + carfentrazone at Adams. Cumulative Russian thistle densities, evaluated monthly throughout the fallow season, were lowest for the sulfentrazone + carfentrazone treatments, except for the late-fall application at Adams. However, flumioxazin + pyroxasulfone and metribuzin provided greater control of tumble mustard and prickly lettuce than did sulfentrazone + carfentazone. Sulfentrazone + carfentrazone, flumioxazin + pyroxasulfone, and metribuzin can all be used for Russian thistle control in fallow. To reduce the risk for crop injury to subsequently planted winter wheat, a late-fall application of sulfentrazone + carfentrazone may be the preferred treatment in low-rainfall regions where winter wheat–fallow is commonly practiced. A late-winter application may be preferred in higher rainfall regions where a 3-year rotation (e.g., winter wheat–spring wheat–fallow) is common. Flumioxazin + pyroxasulfone should be considered if other broadleaf weeds, such as tumble mustard or prickly lettuce, are of concern. The use of these soil-applied herbicides will reduce the need for the frequent application of glyphosate for Russian thistle control in no-till fallow. Nomenclature: Carfentrazone; flumioxazin; glyphosate; metribuzin; pyroxasulfone; sulfentrazone; prickly lettuce; Lactuca serriola L. LACSE; Russian thistle; Salsola tragus L. SASKT; tumble mustard; Sisymbrium altissimum L. SSYAL; winter wheat; Triticum aestivum L.

In semi‐arid climates, seed is often sown into soil with inadequate water for rapid germination. Distinguishing between adequate and marginal water can be difficult. Planting decisions become increasingly complicated when one considers possible differences between cultivars. This study was designed to measure the soil water potential limits for rapid, adequate, and marginal germination of winter wheat (Triticum aestivum L.). Laboratory data showed that germination was rapid (3 to 4 d) in soil at water potentials above ‐1.1 MPa and slower (4 to 5 d) at water potentials that ranged from ‐1.1 to ‐1.6 MPa. Below ‐1.6 MPa, less than half of the experimental units achieved the cut‐off criteria of 75% germination with 5‐mm radical length within 25 d. Six cultivars varied in time to germination by an average of 0.34 d, and two randomly selected seed lots of each cultivar differed by an average of 0.20 d. We conclude that variation between seed lots may be as important as variation between cultivars when looking for seed with superior germination under marginal soil water contents.

Farmers typically use three applications of glyphosate to control weeds in no-till fallow. Some are now experimenting with an unconventional modification to this widely used approach. This modified approach is based on an intentional delay in the time of the first spraying. Farmers delay their first spraying because they want to rely on competition from winter annual grasses to suppress the growth of Russian thistle and eliminate the need for a third application. Optimism for this kind of weed-control program is tempered by concerns related to soil water storage. The objective of this research was to evaluate effects of delayed control of downy brome and volunteer winter wheat on the plant-available water content of, and loss of water from, no-till fallow. Treatments, applied to plots arranged in a randomized complete block design with four replications, were distinguished by the time of the initial glyphosate application. The initial early-season treatment was applied as soon as possible after emergence of downy brome and volunteer winter wheat. Initial mid-season and late-season treatments were applied 4 and 6 wk later, respectively. The amount of plant-available water in the soil profile ranged from 71.8 to 153.7 mm in May and 16.5 to 80.9 mm in September. Water loss was usually minimized in plots treated with the initial early-season treatment. An exception to this trend occurred at a site where the density of downy brome and volunteer winter wheat was greater than average. Abated water loss from the initial late-season treatment, at this site, may have been a consequence of reduced evaporation caused by a decrease in near-surface wind speed and deflection of solar radiation away from soil. Estimated impacts of water loss on grain yield of winter wheat, produced the year after fallow, range from 269 to 600 kg ha−1. Nomenclature: Glyphosate; downy brome, Bromus tectorum L.; Russian thistle, Salsola tragus L.; winter wheat, Triticum aestivum L. Los productores típicamente usan tres aplicaciones de glyphosate para controlar malezas en barbecho con labranza cero. Algunos están actualmente experimentando con una modificación no-convencional a esta práctica ampliamente usada. Esta modificación está basada en un atraso intencional en el momento de la primera aplicación. Los productores atrasan su primera aplicación porque ellos quieren beneficiarse de la competencia de las gramíneas anuales de invierno para suprimir el crecimiento de Salsola tragus y así eliminar la necesidad de una tercera aplicación. El optimismo por este tipo de control de malezas se enfrenta a las preocupaciones relacionadas al almacenaje de agua en el suelo. El objetivo de esta investigación fue evaluar los efectos del retraso en el control de Bromus tectorum y el trigo de invierno voluntario sobre el contenido de agua de suelo disponible para las plantas, y la pérdida de agua en barbechos bajo labranza cero. Los tratamientos fueron distinguidos por el momento de la aplicación inicial de glyphosate y fueron arreglados en un diseño de bloques completos aleatorizados con cuatro repeticiones. El tratamiento inicial temprano durante la temporada fue aplicado tan pronto fue posible después de la emergencia de B. tectorum y del trigo de invierno voluntario. Los tratamientos iniciales a la mitad y tarde durante la temporada de crecimiento fueron aplicados 4 y 6 semanas después, respectivamente. La cantidad de agua disponible para las plantas en el perfil del suelo varió de 71.8 a 153.7 mm en Mayo y de 16.5 a 80.9 mm en Septiembre. La pérdida de agua fue usualmente minimizada en parcelas tratadas con el tratamiento inicial temprano en la temporada. Una excepción a esta tendencia ocurrió en un sitio donde la densidad de B. tectorum y del trigo de invierno voluntario fue mayor al promedio. La reducción en la pérdida de agua en el tratamiento de la aplicación inicial temprano en la temporada, en este sitio, podría haber sido una consecuencia de una evaporación reducida causada por una menor velocidad del viento cerca de la superficie del suelo y un cambio en la incidencia solar sobre el suelo. Los impactos de la pérdida de agua sobre el rendimiento de grano del trigo de invierno, producidos un año después del barbecho, variaron entre 260 y 600 kg ha−1.

Fusarium crown rot (FCR) of winter wheat (Triticum aestivum L.), caused by Fusarium pseudograminearm and Fusarium culmorum, is a yield‐limiting disease in arid wheat‐producing areas of the inland Pacific Northwest. Foliar fungicide applications and currently available seed treatments do not control FCR. Alternative crops that provide a rotational benefit to reduce disease are not economically feasible. Major‐gene resistance is unavailable, but there is preliminary evidence that some wheat and barley (Hordeum vulgare L.) cultivars are more resistant than others. We followed up on preliminary work by growing 14 varieties of winter wheat, planted with in‐furrow FCR inoculum, in 2018 and 2019 in Morrow County, Oregon—one of the world's driest wheat producing regions. Two barley cultivars were added to the experiment during the second year of research. Evaluations of cultivar resistance were made by conducting aboveground visual assessments by counting whiteheads, prematurely senesced wheat heads that are indicative of FCR infection. Whitehead count information was correlated with yield and grain volume weight data. Maximum whitehead counts were measured in plots of the FCR‐susceptible check cultivar ‘Stephens’. There was no evidence of a cultivar‐specific relationship between whitehead count and corresponding values for yield and grain volume weight. There was limited evidence that some cultivars have the capacity to compensate for effects of disease. Core Ideas There is evidence that some wheat cultivars have the capacity to compensate for Fusarium crown rot (FCR). It is necessary to corroborate whitehead counts with FCR symptomology on crown tissue. The contradiction of whitehead count data and yield may be due to increased tillering capacity.