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Unoccupied aerial systems (UAS) are becoming a regular tool in agriculture to obtain phenotypic information of plant growth and development. In this study, we collected red, green, and blue (RGB) images using UAS multiple times throughout the growing season from a cotton field experiment conducted in 2016 and 2021. Collected images were processed to obtain digital surface models (DSMs) from which canopy height (CH) measurements were extracted. Crop growth curve was obtained by fitting several non-linear growth functions on the multi-temporal CH measurements. The five-parameter logistic function performed best with highest R 2 (0.98) and lowest RMSE (6.41). The first and second order derivative of the five-parameter logistic function was performed to obtain several canopy growth parameters. These parameters were used to evaluate the maturity of cotton genotypes and correlated with yield. The maximum growth rate was correlated with yield (R 2  = 0.46 in 2016 and R 2  = 0.68 in 2021). Additionally, the time of onset of steady phase was used to rate maturity of the genotypes with 80% accuracy. This study demonstrated an approach to summarize high-resolution multi-temporal data obtained by UAS to better understand crop growth and development with a potential to be used for assessing the maturity of the genotypes, yield estimations, and management decisions of plant growth regulators.

The efficacy of bispyribac-sodium, fenoxaprop + ethoxysulfuron, and penoxsulam + cyhalofop was evaluated against barnyardgrass, Chinese sprangletop, junglerice, and southern crabgrass when applied at four-, six-, and eight-leaf stages. When applied at the four-leaf stage, bispyribac-sodium provided greater than 97% control of barnyardgrass, junglerice, and southern crabgrass; however, it was slightly weak (74% control) on Chinese sprangletop. Irrespective of the weed species, fenoxaprop + ethoxysulfuron provided greater than 97% control when applied at the four-leaf stage. At the same leaf stage, penoxsulam + cyhalofop controlled 89 to 100% barnyardgrass, Chinese sprangletop, and junglerice and only 54% of southern crabgrass. The efficacy of herbicides was reduced when applied at the eight-leaf stage of the weeds; however, at this stage, fenoxaprop + ethoxysulfuron was effective in controlling 99% of Chinese sprangletop. The results demonstrate the importance of early herbicide application in controlling the weeds. The study identified that at the six-leaf stage of the weeds, fenoxaprop + ethoxysulfuron can effectively control Chinese sprangletop and southern crabgrass, penoxsulam + cyhalofop can effectively control Chinese sprangletop, and bispyribac-sodium can effectively control junglerice.

Crop residues acting as mulches can influence weed seedling emergence and weed biomass. A field study was conducted to evaluate the effect of rice residue amounts (0, 3, and 6 t ha−1) on seedling emergence of eight weed species in zero-till dry-seeded rice. The highest seedling emergence of spiny amaranth, southern crabgrass, crowfootgrass, junglerice, eclipta, goosegrass, and Chinese sprangletop was observed in the absence of residue. Seedling emergence of these weeds declined with increasing residue amounts; however, the greatest and most substantial reductions in emergence occurred with 6 t ha−1 of residue. The presence of residue also resulted in less weed biomass than with the no-residue treatment. The emergence and biomass of threelobe morningglory seedlings, however, were not influenced by residue amounts. The use of residue also increased the time taken to reach 50% of maximum emergence for some species, for example, spiny amaranth and Chinese sprangletop. The results of our study suggest that the use of residue at high rates can help suppress seedling emergence and growth of many weeds. However, there is a need to integrate other weed management strategies with residue retention to achieve season-long weed control. Nomenclature: Spiny amaranth, Amaranthus spinosus L. AMASP; crowfootgrass, Dactyloctenium aegyptium (L.) Willd. DTTAE; southern crabgrass, Digitaria ciliaris (Retz.) Koel. DIGSP; junglerice, Echinochloa colona (L.) Link, ECHCO; eclipta, Eclipta prostrata (L.) L. ECLAL; goosegrass, Eleusine indica (L.) Gaertn. ELEIN; threelobe morningglory, Ipomoea triloba L. IPOTR; Chinese sprangletop, Leptochloa chinensis (L.) Nees. LEFCH; rice, Oryza sativa L.

Experiments were conducted in the laboratory and screenhouse to determine the effects of scarification; alternating day/night temperatures; light, salt, and water stress; seed burial depth; and rice residue on seed germination and seedling emergence of threelobe morningglory, and to evaluate the response of this weed to commonly available POST herbicides in the Philippines. Germination was stimulated by seed scarification, suggesting that inhibition of germination in this species is mainly due to the hard seed coat. Germination of the scarified seeds was not influenced by the tested temperatures (alternating day/night temperatures of 25/15, 30/20, and 35/25 C) and light. The concentrations of sodium chloride, ranging from 0 to 250 mM, did not influence germination of the scarified seeds of threelobe morningglory. The osmotic potential required for 50% inhibition of maximum germination was −0.35 MPa, although some seeds germinated at −0.6 MPa. Seedling emergence was greatest for the seeds placed on the soil surface (96%), and emergence declined with increased burial depth in soil. The burial depth required for 50% inhibition of maximum emergence was 2.8 cm. No seedlings emerged from a burial depth of 6 cm or greater. Residues of up to 6 Mg ha−1 on the soil surface did not influence seedling emergence of threelobe morningglory. The herbicide 2,4-D at 400 g ai ha−1 provided excellent control of threelobe morningglory when applied at the four-leaf (100%) and six-leaf (97%) stages. However, at the eight-leaf stage, percent control was reduced to 67% and herbicide rate had to be increased twofold to achieve 95% control. The information gained from this study could contribute to developing components of integrated weed management strategies for threelobe morningglory. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence and early application of an effective POST herbicide could serve as important tools for managing threelobe morningglory. Nomenclature: 2,4-D; glyphosate; metsulfuron + chlorimuron; threelobe morningglory, Ipomoea triloba L. IPOTR; rice, Oryza sativa L.

Studies were conducted in a screenhouse to determine the interaction of rice residue as mulch (0, 3, and 6 t ha−1) and herbicides (nontreated, oxadiazon at 0.5 and 1.0 kg ai ha−1, and pendimethalin at 1.0 and 2.0 kg ai ha−1) on seedling emergence and biomass of barnyardgrass, crowfootgrass, junglerice, and rice flatsedge. Regardless of the residue amount, crowfootgrass and junglerice were effectively controlled by all herbicide treatments. No seedlings of these weed species escaped the herbicides when applied in the presence of residue cover. There was no survival of barnyardgrass seedlings when both herbicides were applied on bare soil (without residue cover); however, some seedlings survived oxadiazon and pendimethalin when applied in the presence of residue cover. For rice flatsedge, the herbicide applications in the presence of residue cover resulted in lower weed control than in the absence of residue. These results suggest that some weed species can escape the application of PRE herbicides in conservation agriculture systems in which residue can bind soil-applied herbicides and result in lower efficacy. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; crowfootgrass, Dactyloctenium aegyptium (L.) Willd. DTTAE; junglerice, Echinochloa colona (L.) Link. ECHCO; rice flatsedge, Cyperus iria L. CYPIR; rice, Oryza sativa L. ORYSA Se realizaron estudios en un invernadero para determinar la interacción de los residuos del arroz como cobertura (0, 3 y 6 t ha−1) y herbicidas (testigo no-tratado, oxadiazon a 0.5 y 1.0 kg ai ha−1, y pendimethalin a 1.0 y 2.0 kg ai ha−1) sobre la emergencia de plántulas y la biomasa de Echinochloa crus-galli, Dactyloctenium aegyptium, Echinochloa colona y Cyperus iria. Sin importar la cantidad de cobertura, D. aegyptium y E. colona fueron controladas efectivamente por todos los tratamientos de herbicidas. Ninguna plántula de estas especies de malezas escaparon a los herbicidas cuando se aplicó en presencia de la cobertura con residuos de arroz. No hubo sobrevivencia de plántulas de E. crus-galli, cuando ambos herbicidas se aplicaron sobre suelo desnudo (sin cobertura de residuos); sin embargo, algunas plántulas sobrevivieron a oxadiazon y pendimethalin cuando estos se aplicaron en presencia de la cobertura de residuos. Para C. iria, las aplicaciones de herbicidas en presencia de la cobertura resultó en menor control que en la ausencia de residuos. Estos resultados sugieren que algunas especies de malezas pueden escapar a las aplicaciones de herbicidas PRE en sistemas de agricultura de conservación en los cuales los herbicidas aplicados al suelo pueden adherirse a los residuos disminuyendo su eficacia.

Weeds are the main constraint in the adoption of zero-till, dry-seeded rice systems because weeds and rice emerge simultaneously in these systems, and there is no standing water at crop establishment to suppress weeds. A study was conducted during the wet season of 2011 and the dry season of 2012 at the International Rice Research Institute to evaluate the performance of different herbicides in mechanized-sown, zero-till dry-seeded rice. Among the treatments evaluated, oxadiazon followed by penoxsulam + cyhalofop followed by one hand-weeding at 42 d after sowing, provided 23 to 35% higher yield than the nontreated control. The yields in the oxadiazon-treated plots were similar to those in the weed-free plots. Some weed species, including eclipta and doveweed, were not controlled by the evaluated herbicides. Therefore, there is a need to evaluate additional herbicides and to integrate them with cultural weed management strategies to manage such problematic weeds. Nomenclature: Cyhalofop; oxadiazon; penoxsulam; doveweed; Murdannia nudiflora (L.) Brenan MUDNU; eclipta; Eclipta prostrata (L.) L. ECLAL; rice; Oryza sativa L. ORYSA Las malezas son la principal limitante para la adopción de la labranza cero en sistemas de arroz sembrado en secano porque en estos sistemas las malezas y el arroz emergen simultáneamente y no hay una lámina de agua presente que suprima las malezas al momento del establecimiento del cultivo. Se realizó un estudio durante la época lluviosa de 2011 y la época seca de 2012 en el Instituto Internacional de Investigaciones sobre el Arroz para evaluar el desempeño de diferentes herbicidas en siembra mecanizada, labranza cero y siembra de arroz de secano. Entre los tratamientos evaluados, oxadiazon seguido de penoxsulam + cyhalofop seguido por una deshierba manual a 42 d después de la siembra, resultó en un rendimiento 23 a 35% mayor que el testigo no-tratado. Los rendimientos en las parcelas tratadas con oxadiazon fueron similares a los de las parcelas libres de malezas. Algunas especies de malezas, incluyendo Eclipta prostrata y Murdannia nudiflora, no fueron controladas por los herbicidas evaluados. Por esta razón, existe la necesidad de evaluar herbicidas adicionales y su integración con estrategias de manejo cultural para el manejo de estas malezas problemáticas.

In Asia, a significant area under rice is affected by salinity. Salt stress can affect growth of crops as well as weeds. A study was conducted in a greenhouse to determine the effect of salinity (electrical conductivity [EC] of 1, 6, 12, 18, and 24 dS m−1) on growth of barnyardgrass, horse purslane, junglerice, and rice. Growth variables were analyzed using regression analysis. The tested levels of EC influenced leaf production of barnyardgrass and junglerice but not that of horse purslane. As compared with the control treatment (EC of 1 dS m−1), shoot biomass of barnyardgrass decreased by only 24% at 12 dS m−1, whereas rice biomass declined by 59% at this level of EC. At EC of 24 dS m−1, barnyardgrass still produced 4% of the biomass of the control treatment, whereas rice did not survive at this level of EC. Junglerice shoot biomass decreased by 73% at 18 dS m−1 EC compared with the control treatment, whereas rice shoot biomass declined by more than 86% at 18 dS m−1 EC. An EC of 10 dS m−1 was required to inhibit 50% shoot biomass of rice, whereas the EC to inhibit 50% shoot biomass of barnyardgrass and junglerice was 15 and 13 dS m−1, respectively. Shoot biomass of horse purslane was not influenced by the tested levels of EC. At the highest EC (24 dS m−1), at which rice did not survive, horse purslane shoot biomass was similar to that of the control treatment. In all weed species, data for root biomass showed trends similar to those of shoot biomass. The results of this study suggest that weeds were more tolerant to salt than rice, and horse purslane was the most tolerant species among the weeds. Nomenclature: Junglerice, Echinochloa colona (L.) Link., ECHCO; barnyardgrass, E. crus-galli (L.) Beauv., ECHCG; horse purslane, Trianthema portulacastrum L., TRIPO; rice, Oryza sativa L., ORYSA.

The growth of spiny amaranth and longfruited primrose-willow was studied by growing them alone and in competition with 4 and 12 rice (cv. RC222) plants. Interference with 12 rice plants reduced the height of spiny amaranth beyond 6 wk after planting. The height of longfruited primrose-willow was significantly reduced by the crop interference starting from 4 wk after planting. Both weed species showed the ability to reduce the effects of rice interference by increasing leaf area, leaf and stem biomass in the upper half of the plant, and specific stem length. At 9 wk after planting, for example, longfruited primrose-willow had 89 and 99% leaf biomass in the upper half of the plant when grown with 4 and 12 rice plants compared with only 34% when grown alone. These values for spiny amaranth were 15, 29, and 72% when grown alone, with 4 rice plants, and 12 rice plants, respectively. Despite such plasticity, spiny amaranth's aboveground biomass at final harvest was reduced by 34 and 70% when grown with 4 and 12 rice plants, respectively, compared with its biomass without crop interference. The corresponding values for longfruited primrose-willow were 92 and 98%, respectively. These results suggest that uniform and high crop density could be an important tool to reduce competition from these weeds in direct-seeded rice.

Field surveys were conducted across the Blacklands region of Texas during 2016 and 2017 to document the distribution of herbicide-resistant Lolium spp. infesting winter wheat production fields in the region. A total of 68 populations (64 Italian ryegrass, four perennial ryegrass) were evaluated in a greenhouse for sensitivity to herbicides of three different modes of action: an acetolactate synthase (ALS) inhibitor (mesosulfuron-methyl), two acetyl-coenzyme-A carboxylase (ACCase) inhibitors (diclofop-methyl and pinoxaden), and a 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitor (glyphosate). Herbicides were applied at twice the label-recommended rates for mesosulfuron-methyl (29 g ai ha–1), diclofop-methyl (750 g ai ha–1), and pinoxaden (118 g ai ha–1); and at the recommended rate for glyphosate (868 g ae ha–1). The herbicide screenings were followed by dose-response assays of the most-resistant ryegrass population for each herbicide at eight rates (0.5, 1, 2, 4, 8, 16, 32, and 64×), compared with a susceptible population at six rates (0.0625, 0.125, 0.25, 0.5, 1, and 2×). The initial screening and dose-response experiments were conducted in a completely randomized design with three replications and two experimental runs. Survivors (<80% injury) were characterized as highly resistant (0% to 20% injury) or moderately resistant (21% to 79%). Results showed that 97%, 92%, 39%, and 3% of the Italian ryegrass populations had survivors to diclofop-methyl, mesosulfuron-methyl, pinoxaden, and glyphosate treatments, respectively. Of the four perennial ryegrass populations, three were resistant to diclofop-methyl and mesosulfuron-methyl, and one was resistant to pinoxaden as well. Perennial ryegrass populations did not exhibit any resistance to glyphosate. Dose-response assays revealed 37-, 196-, and 23-fold resistance in Italian ryegrass to mesosulfuron-methyl, diclofop-methyl, and pinoxaden, respectively, compared with a susceptible standard. One Italian ryegrass population exhibited three-way multiple resistance to ACCase-, ALS-, and EPSPS-inhibitors. The proliferation of multiple herbicide–resistant ryegrass is a challenge to sustainable wheat production in Texas Blacklands and warrants diversified management strategies.

The genus Echinochloa constitutes some of the most prominent weed species found in rice (Oryza sativa L.) production worldwide. The taxonomy of Echinochloa is complex due to its morphological variations. The morphophysiological diversity and taxonomic characteristics of Echinochloa ecotypes infesting rice fields in Texas are unknown. A total of 54 Echinochloa ecotypes collected during late-season field surveys in 2015 and 2016 were characterized in a common garden in 2017. Plants were characterized for 14 morphophysiological traits, including stem angle; stem color; plant height; leaf color; leaf texture; flag leaf length, width, and angle; days to flowering; panicle length; plant biomass; seed shattering; seed yield; and seed dormancy. Principal component analysis indicated that 4 (plant height, flag leaf length, seed shattering, and seed germination) of the 14 phenological traits characterized here had significantly contributed to the overall morphological diversity of Echinochloa spp. Results showed wide interpopulation diversity for the measured traits among the E. colona ecotypes, as well as diverse intrapopulation variability in all three Echinochloa species studied, including barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], junglerice [Echinochloa colona (L.) Link], and rough barnyardgrass [Echinochloa muricata (P. Beauv.) Fernald]. Taxonomical classification revealed that the collection consisted of three Echinochloa species, with E. colona being the most dominant (96%), followed by E. crus-galli (2%), and E. muricata (2%). Correlation analysis of morphophysiological traits and resistance status to commonly used preemergence (clomazone, quinclorac) and postemergence herbicides (propanil, quinclorac, imazethapyr, and fenoxaprop-ethyl) failed to show any significant association. Findings from this study provided novel insights into the morphophysiological characteristics of Echinochloa ecotypes in rice production in Texas. The morphological diversity currently present in Echinochloa ecotypes could contribute to their adaptation to selection pressure imposed by different management tools, emphasizing the need for a diversified management approach to effectively control this weed species.