Alexander Menegat

Japanese Bindweed (Calystegia hederacea) Abundance and Response to Winter Wheat Seeding Rate and Nitrogen Fertilization in the North China Plain

Abstract Japanese bindweed was found to be one of the most abundant and most difficult-to-control weed species during a 2-yr weed survey in more than 100 winter wheat fields in the North China Plain region. Multivariate data analysis showed that Japanese bindweed is most abundant at sites with comparative low nitrogen (N) fertilization intensities and low crop densities. To gain deeper insights into the biology of Japanese bindweed under various N fertilization intensities, winter wheat seeding rates, herbicide treatments, and their interactions, a 2-yr field experiment was performed. In nonfertilized plots, a herbicide efficacy (based on density reduction) of 22% for 2,4-D, and of 25% for tribenuron-methyl was found. The maximum herbicide efficacy in Nmin-fertilized plots (target N value based on expected crop yield minus soil mineral nitrogen content,) was 32% for 2,4-D and 34% for tribenuron-methyl. In plots fertilized according to the farmers practices, a maximum herbicide efficacy of 72% for 2,4-D and of 64% for tribenuron-methyl could be observed. Furthermore, medium and high seeding rates improved the herbicide efficacy by at least 39% for tribenuron-methyl and 44% for 2,4-D compared to the low seeding rate. Winter wheat yield was not significantly affected by seeding rate itself, whereas at low and medium seeding rates, Nmin fertilization was decreasing winter wheat yield significantly compared to the farmers usual fertilization practice. At the highest seeding rate, Nmin fertilization resulted in equal yields compared to the farmers practices of fertilization. Nomenclature: 2,4-D; tribenuron-methyl; Japanese bindweed; Calystegia hederacea Wallich CAGHE; wheat; Triticum aestivum L. Resumen Se encontró que Calystegia hederacea fue una de las especies de malezas más abundantes y más difíciles de controlar en un estudio observacional de 2 años de duración en más de 100 campos de trigo de invierno en la región de las Planicies del Norte de China. Análisis multivariado de datos mostró que C. hederacea es más abundante en sitios con niveles comparativos bajos de intensidad de fertilización con nitrógeno (N) y densidades de cultivo bajas. Para ganar un mayor conocimiento sobre la biología de C. hederacea bajo intensidades variables de N, densidades de siembra de trigo de invierno, tratamientos con herbicidas, y sus interacciones, se realizó un experimento de campo durante 2 años. En parcelas sin fertilización, se encontró una eficacia del herbicida (basada en reducción de la densidad de la maleza) de 22% con 2,4-D, y de 25% con tribenuron-methyl. La eficacia máxima de herbicidas, en parcelas fertilizadas usando el método Nmin, fue 32% con 2,4-D y 34% con tribenuron-methyl. En las parcelas fertilizadas de acuerdo a las prácticas de los productores, la eficacia máxima del herbicida observada fue 72% para 2,4-D y 64% para tribenuron-methyl. Además, densidades de siembra medias y altas mejoraron la eficacia del herbicida en al menos 39% con tribenuron-methyl y 44% con 2,4-D al comparase con la densidad de siembra baja. El rendimiento del trigo de invierno no fue afectado significativamente por la densidad de siembra, mientras que en las densidades de siembra baja y media, la fertilización Nmin disminuyó el rendimiento del trigo de invierno significativamente, al compararse con las prácticas de fertilización usuales de los productores. En la densidad de siembra alta, la fertilización Nmin resultó en rendimientos iguales en comparación con las prácticas de fertilización de los productores.

The Mechanism of Methylated Seed Oil on Enhancing Biological Efficacy of Topramezone on Weeds

Methylated seed oil (MSO) is a recommended adjuvant for the newly registered herbicide topramezone in China and also in other countries of the world, but the mechanism of MSO enhancing topramezone efficacy is still not clear. Greenhouse and laboratory experiments were conducted to determine the effects of MSO on efficacy, solution property, droplet spread and evaporation, active ingredient deposition, foliar absorption and translocation of topramezone applied to giant foxtail (Setaria faberi Herrm.) and velvetleaf (Abutilon theophrasti Medic.). Experimental results showed that 0.3% MSO enhanced the efficacy of topramezone by 1.5-fold on giant foxtail and by 1.0-fold on velvetleaf. When this herbicide was mixed with MSO, its solution surface tension and leaf contact angle decreased significantly, its spread areas on weed leaf surfaces increased significantly, its wetting time was shortened on giant foxtail but not changed on velvetleaf, and less of its active ingredient crystal was observed on the treated weed leaf surfaces. MSO increased the absorption of topramezone by 68.9% for giant foxtail and by 45.9% for velvetleaf 24 hours after treatment. It also apparently promoted the translocation of this herbicide in these two weeds.

Soil water potential and temperature sum during reproductive growth control seed dormancy in Alopecurus myosuroides Huds.

Abstract The sustainable management of unwanted vegetation in agricultural fields through integrated weed control strategies requires detailed knowledge about the maternal formation of primary seed dormancy, to support the prediction of seedling emergence dynamics. This knowledge is decisive for the timing of crop sowing and nonchemical weed control measures. Studies in controlled environments have already demonstrated that thermal conditions and, to some extent, water availability during seed set and maturation has an impact on the level of dormancy. However, it is still unclear if this applies also under field conditions, where environmental stressors and their timing are more variable. We address this question for Alopecurus myosuroides in south‐western Sweden. We quantified the effects of cumulated temperature and precipitation as well as soil water potential during the reproductive growth phase of A myosuroides on primary seed dormancy under field conditions. Empirical models differing in focal time intervals and, in case of soil water potential, focal soil depths were compared regarding their predictive power. The highest predictive power for the level of primary dormancy of A. myosuroides seeds was found for a two‐factorial linear model containing air temperature sum between 0 and 7 days before peak seed shedding as well as the number of days with soil water potential below field capacity between 7 and 35 days before peak seed shedding. For soil water potential, it was found that only the top 10 cm soil layer is of relevance, which is in line with the shallow root architecture of A. myosuroides. We conclude that for this species the level of dormancy depends on the magnitude and timing of temperature and water availability during the reproductive growth phase. Water availability appears to be more important during maternal environmental perception and temperature during zygotic environmental perception.