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Two separate field experiments were conducted during the 2021 to 2022 and 2022 to 2023 growing seasons at Kansas State University Agricultural Research Center near Hays, KS, to understand the emergence dynamics of glyphosate-resistant (GR) kochia [Bassia scoparia (L.) A. J. Scott] as influenced by fall- and spring-planted cover crops (CC) and residual herbicide. Study sites were under winter wheat (Triticum aestivum L.)–sorghum [Sorghum bicolor (L.) Moench]–fallow rotation with a natural seedbank of GR B. scoparia. In Experiment 1, fall-planted CC mixture (triticale/winter peas/radish/canola) was planted after wheat harvest and terminated at triticale [×Triticosecale Wittm. ex A. Camus [Secale × Triticum] heading stage (next spring before sorghum planting). In Experiment 2, spring-planted CC mixture (oats/barley/spring peas) was planted in sorghum stubbles and terminated at oats (Avena sativa L.) heading stage. Four treatments were established in each experiment: (1) nontreated control (no CC and no herbicide), (2) chemical fallow (no CC but glyphosate + acetochlor/atrazine or flumioxazin/pyroxasulfone + dicamba were used to control weeds), (3) CC terminated with glyphosate, and (4) CC terminated with glyphosate plus residual herbicide (acetochlor/atrazine for fall-planted CC and flumioxazin/pyroxasulfone for spring-planted CC). Results indicated that fall-planted CC delayed GR B. scoparia emergence by 3 to 5 wk, whereas spring-planted CC delayed emergence by 0 to 2 wk compared with nontreated control. Fall-planted CC terminated with glyphosate plus acetochlor/atrazine reduced the cumulative emergence of GR B. scoparia by 90% to 95% compared with nontreated control across both years. Similarly, spring-planted CC terminated with glyphosate plus flumioxazin/pyroxasulfone reduced the cumulative emergence of GR B. scoparia by 83% to 90% compared with nontreated control. These results suggest that fall- or spring-planted CC in combination with residual herbicide at termination can be utilized for GR B. scoparia suppression. Results from this study will help in developing prediction models for GR B. scoparia emergence under different CC strategies.

A field study was conducted from 2020 to 2023 at Kansas State University Agricultural Research Center near Hays, KS, to understand the emergence dynamics and periodicity of glyphosate-resistant (GR) Palmer amaranth (Amaranthus palmeri S. Watson) as influenced by cover crop (CC) residue and residual herbicide in grain sorghum [Sorghum bicolor (L.) Moench]. The study site was under a wheat (Triticum aestivum L.)–sorghum–fallow rotation with a natural seedbank of GR A. palmeri. Treatments included (1) fall-planted CC mixture [winter triticale (×Triticosecale Wittm. ex A. Camus [Secale × Triticum])/winter peas (Pisum sativum L.)/ rapeseed (Brassica napus L.)/radish (Raphanus sativus L.)] after wheat harvest and terminated at triticale heading stage (next spring before sorghum planting) with glyphosate alone or (2) glyphosate plus acetochlor/atrazine, (3) chemical fallow (no CC but treated with acetochlor/ atrazine and dicamba before sorghum planting), and (4) nontreated control (no CC and no herbicide). Results indicated that CC terminated with glyphosate plus acetochlor/atrazine had a delayed and reduced cumulative emergence of GR A. palmeri as compared with chemical fallow and CC terminated with glyphosate alone across all 3 yr. Compared with chemical fallow, the CC terminated with glyphosate alone and glyphosate plus acetochlor/atrazine required 66 to 643 and 105 to 1,257 more cumulative growing degree days, respectively, to achieve 90% cumulative emergence of GR A. palmeri across all 3 yr. The combined effect of CC residue with glyphosate plus acetochlor/atrazine reduced the total emergence counts of GR A. palmeri by 42% to 56% and 82% to 94% as compared with chemical fallow and nontreated control, respectively. These results suggest that fall-planted CC combined with a residual herbicide at termination can be utilized for GR A. palmeri suppression in grain sorghum.

The evolution of multiple herbicide-resistant weeds, including Palmer amaranth, has necessitated the implementation of an integrated weed management (IWM) program. Understanding weed emergence patterns is critical for developing effective IWM strategies. The objective of this study was to evaluate the effect of tillage timings and residual herbicides on cumulative emergence and emergence pattern of Palmer amaranth. Field experiments were conducted in 2015 and 2016 in a field naturally infested with photosystem (PS) II and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor-resistant Palmer amaranth near Shickley, Nebraska, in a bare ground study, with no crop planted in the plots, although residues from the preceding corn crop were present on the soil surface. Treatments consisted of shallow tillage timings (early, mid, and late), three premix corn or soybean residual herbicides, and a nontreated control. The Weibull function was fitted to cumulative Palmer amaranth emergence with day of year (DOY) and thermal time (TT) as independent variables. Year by treatment interaction was significant for time to 10%, 25%, 50%, 75%, and 90% Palmer amaranth emergence and cumulative emergence. The majority of Palmer amaranth seedlings emerged early, following early tillage with 90% cumulative emergence occurring on DOY 172 compared with DOY 210 to 212 for mid- and late-tillage, and DOY 194 for the nontreated control in 2015. In 2016, 90% of cumulative emergence following early-, mid-, and late-tillage (DOYs 201 to 211) were similar, and that of the nontreated control (DOY 188) was similar to that of early tillage. Nontreated control and PRE herbicide treatments had similar DOY values for 90% emergence in both years. The number of emerged Palmer amaranth seedlings over the season was higher with shallow tillage than no tillage or with the use of PRE herbicides. Nomenclature: Atrazine; bicyclopyrone; chlorimuron; flumioxazin; fluthiacet; mesotrione; pyroxasulfone; S-metolachlor; Palmer amaranth; Amaranthus palmeri S. Watson

Field experiments were conducted in the growing seasons of 2017 to 2018 and 2018 to 2019 to evaluate the competitive effects of rattail fescue [Vulpia myuros (L.) C.C. Gmel.] in winter wheat (Triticum aestivum L.) and to assess whether delayed crop sowing and increased crop density influence the emergence, competitiveness, and fecundity of V. myuros. Cumulative emergence showed the potential of V. myuros to emerge rapidly and under a wide range of climatic conditions with no effect of crop density and variable effects of sowing time between the two experiments. Grain yield and yield components were negatively affected by increasing V. myuros density. The relationship between grain yield and V. myuros density was not influenced by sowing time or by crop density, but crop–weed competition was strongly influenced by growing conditions. Due to very different weather conditions, grain yield reductions were lower in the growing season of 2017 to 2018 than in 2018 to 2019, with maximum grain yield losses of 22% and 50% in the two growing seasons, respectively. The yield components, number of crop ears per square meter, and 1,000-kernel weight were affected almost equally, reflecting that V. myuros’s competition with winter wheat occurred both early and late in the growing season. Seed production of V. myuros was suppressed by delaying sowing and increasing crop density. The impacts of delayed sowing and increasing crop density on seed production of V. myuros highlight the potential of these cultural weed control tactics in the long-term management programs of this species.

Experiments were conducted in 2008 and 2009 in Fayetteville, AR, to determine the influence of late-season herbicide applications on control, seed reduction, seed viability, and seedling fitness of two glyphosate-resistant (GR) Palmer amaranth biotypes, one from Mississippi County (MC) and the other from Lincoln County (LC) in Arkansas. Glyphosate (870 g ae ha−1), glufosinate (820 g ai ha−1), 2,4-D amine (1,060 g ae ha−1), dicamba (280 g ae ha−1), and pyrithiobac (70 g ai ha−1) were each applied at the first visible sign of inflorescence of GR Palmer amaranth plants. Glufosinate, 2,4-D, and dicamba provided 52 to 74% control of MC GR Palmer amaranth plants 28 d after treatment (DAT). The LC biotype was larger (94 cm tall) than the MC biotype was (64 cm tall) at application and was more difficult to control. Although control of GR Palmer amaranth was inadequate, late-season applications of glufosinate, 2,4-D, and dicamba reduced seed production of the LC biotype by 75 to 87% and production of the MC biotype by 94 to 95% compared with nontreated plants. Irrespective of biotypes, glufosinate, 2,4-D, and glyphosate reduced 100-seed weight by 22% compared with the nontreated control, and viability of seeds produced by treated plants was only 45 to 61% compared with 97% seed viability in nontreated plants. Glyphosate, glufosinate, 2,4-D, or dicamba reduced cumulative seedling emergence by an average of 84% compared with the nontreated check. Seedling biomass was four times greater for the LC than for the MC biotype, suggesting greater vigor and fitness for the LC progeny. This research demonstrates that a single, late-season (early inflorescence stage) application of glufosinate, 2,4-D, or dicamba could potentially reduce seedbank replenishment of GR Palmer amaranth. Additionally, reduction in seed weight, viability, and seedling recruitment would impair the success of GR Palmer amaranth progeny in the following season. Nomenclature: 2,4-D amine; dicamba; glufosinate; glyphosate; pyrithiobac; Palmer amaranth, Amaranthus palmeri S. Wats. Se realizaron experimentos en 2008 y 2009 en Fayetteville, AR, para determinar la influencia de aplicaciones de herbicidas tarde en la temporada de producción sobre el control, la reducción en la producción de semilla, la viabilidad de la semilla y el desempeño de las plántulas de dos biotipos de Amaranthus palmeri resistentes a glyphosate (GR), uno del condado de Mississippi (MC) y el otro del condado Lincoln (LC) en Arkansas. Glyphosate (870 g ae ha−1), glufosinate (820 g ai ha−1), 2,4-D amine (1,060 g ae ha−1), dicamba (280 g ae ha−1) y pyrithiobac (70 g ai ha−1), fueron aplicados al primer signo visible de las inflorescencias de las plantas de A. palmeri GR. Glufosinate, 2,4-D y dicamba brindaron un control de 52 a 74% de las plantas MC de A. palmeri GR 28 días después del tratamiento (DAT). El biotipo LC fue más grande (94 cm de altura) que el biotipo MC (64 cm de altura) al momento de la aplicación y fue más difícil de controlar. Aunque el control de A. palmeri GR fue inadecuado, las aplicaciones tardías en la temporada con glufosinate, 2,4-D y dicamba redujeron la producción de semillas del biotipo LC de 75 a 87% y 94 a 95% del biotipo MC en comparación con las plantas no-tratadas. Independientemente del biotipo, glufosinate, 2,4-D y glyphosate redujeron el peso 100-semillas en 22% comparados con el testigo no-tratado, y la viabilidad de las semillas producidas por las plantas tratadas fue solamente 45 al 61% comparadas con 97% de viabilidad de las plantas no-tratadas. Glyphosate, glufosinate, 2,4-D o dicamba redujeron la emergencia acumulada de plántulas en un promedio de 84% comparadas con el testigo no-tratado. La biomasa de las plántulas fue cuatro veces mayor para el biotipo LC que para el MC, sugiriendo un mayor vigor y aptitud en la progenie de LC. Esta investigación demuestra que una sola aplicación, tarde en la temporada (inicio de floración de la maleza), de glufosinate, 2,4-D o dicamba puede potencialmente reducir la renovación del banco de semillas de A. palmeri GR. Adicionalmente, la reducción en el peso de la semilla, viabilidad y la emergencia de plántulas podría afectar negativamente el éxito de la progenie de A. palmeri GR en la siguiente temporada de producción.

Larix olgensis is one of the important commercial timber tree species in northeastern China, but it does not naturally regenerate in L. olgensis forests even after cutting. To identify the causes of the regeneration failure, the authors tested the effects of site preparation in a thinned stand and in a clearcut on the emergence and early establishment of L. olgensis seedlings. The results indicated that there was no correlation between cumulative emergence percentage (CEP) of L. olgensis seedlings and canopy openness, but the CEP was significantly affected by site preparation (P < 0.001). The average seedling survival rates after treatments consisting of removing both litter cover and understory vegetation cover were significantly higher in the clearcut than in the thinned stand (P < 0.001). Without site preparation, all seedlings in both the thinned stand and the clearcut disappeared within the first growing season, meaning that ground cover (understory vegetation cover and litter cover) was not beneficial to seedling survival. The average growth of seedlings exhibited significant differences between the thinned stand and the clearcut, and among the site preparations (P < 0.001). Intensely thinned stands without ground cover improved seedling growth. These results imply that light and ground cover might be the main factors limiting the early establishment of L. olgensis seedlings in managed plantation forests

Understanding how the emergence of the anthropogenic warming signal from the noise of internal variability translates to changes in extreme event occurrence is of crucial societal importance. By utilising simulations of cumulative carbon dioxide (CO2) emissions and temperature changes from eleven earth system models, we demonstrate that the inherently lower internal variability found at tropical latitudes results in large increases in the frequency of extreme daily temperatures (exceedances of the 99.9th percentile derived from pre-industrial climate simulations) occurring much earlier than for mid-to-high latitude regions. Most of the world's poorest people live at low latitudes, when considering 2010 GDP-PPP per capita; conversely the wealthiest population quintile disproportionately inhabit more variable mid-latitude climates. Consequently, the fraction of the global population in the lowest socio-economic quintile is exposed to substantially more frequent daily temperature extremes after much lower increases in both mean global warming and cumulative CO2 emissions.

A study assessed the potential for using cumulative growing degree days (CGDD) to predict the weed emergence periodicity of three weed species: Argemone mexicana, Brassica tournefortii, and Rapistrum rugosum. Weed emergence was monitored regularly by placing 200 fresh seeds of each weed species on the soil surface. Weed emergence data was fit using a three-parameter sigmoidal Gompertz model. The CGDD required for 50% emergence of A. mexicana ranged from 3380 to 5302, depending upon the seasonal variation in temperature and rainfall. The majority of emergence appeared from March to June. The seeds of A. mexicana exhibited dormancy, as the majority of seeds germinated in the second season. The CGDD required for 50% emergence of B. tournefortii ranged from 824 to 2311, depending upon the seasonal variation in temperature and intensity of rainfall. Most cohorts of B. tournefortii appeared in the first season from February to June, indicating little dormancy in seeds. The CGDD required for 50% emergence of R. rugosum ranged from 2242 to 2699, depending upon weather parameters (temperature and rainfall). The main cohorts of R. rugosum appeared from February to June, and 60% of seeds germinated in the first season, while 40% germinated in the second season, indicating dormancy in seeds. The coefficients of determination for the model verification on the emergence pattern of three weeds were > 85%, suggesting that CGDD are good predictors for the emergence of these weeds. These results suggest that forecasting the emergence of three weed species on the basis of CGDD and rainfall patterns will help growers to make better weed management decisions.

Water deficit is one of the major limiting factors of seed crop germination and productivity. Consequently, superabsorbent polymers (SAPs) are among several technologies that enhance water use efficiency, leading to worthy seed germination. The objective of this study was to investigate the potential effect of three rates of SAPs (0.0%, 0.5%, and 1.0% w/w) on the seedling emergence of barley and fenugreek sown in a sandy soil using three replicates in a randomized complete block design. Outdoor pot experiments were conducted in Aswan Province, Egypt. The differences in the final germination percentages (FGPs) were not significant for both seeds, while the application of SAPs enhanced the seedling germination index (GI) with significant differences for both crop seeds. The application of SAP at 0.5% gave the highest GI for barley (2.47 day−1) and fenugreek (2.66 day−1) seeds. The sigmoidal function effectively described the cumulative germination percentage rates for both seeds as a function of time under the SAP levels with R2 greater than 0.992. The maximum rates were 69.4 and 64.6 day−1 for barley and fenugreek seeds at SAP 0.5%, respectively. The corresponding rates for 0.0% SAP were 11 and 12 day−1. The water germination efficiencies (WGE) were 27.76 and 30.04 cm−1 for 0.0% and 0.5% SAP for barley, while they were 23.07 and 29.9 cm−1 for fenugreek. Accordingly, SAPs could represent a promising solution for increasing moisture conservation for seed germination in a sand soil. For strategic management, barley is recommended for growth over fenugreek in a semidried soil.

We investigated changes in the developmental duration of rice cultivars with a wide range of maturities in response to late planting. Elucidating the relationship between cropping season and the progress of growth stages is important for establishing direct-seeded cultivation and creating growth models. Late planting of the intermediate to late maturing cultivars Akidawara and Hoshijirushi decreased the time from emergence to panicle formation and decreased the cumulative effective temperature (CET) and cumulative effective soil temperature (CEST). In the very early maturing cultivars Ichibanboshi and Fusakogane, the changes in number of days, CET, and CEST from emergence to panicle formation with late planting were small. From emergence to heading and maturity, the number of days, CET, and CEST of many cultivars tended to increase until mid-May and then decreased. The changes in the number of days, CET, and CEST caused by late planting were greater for the intermediate to late maturing cultivars than for the very early maturing cultivars. The differences between cultivars were greatest with early May sowing, and then decreased with later planting. Short-day condition revealed significant differences in the duration of vegetative growth and CET among cultivars, but long-day condition erased these differences. These results demonstrate that the photosensitivity and thermosensitivity of cultivars are especially important in crop planning and for creating growth models of direct-seeded rice.