Time Of Herbicide Application Research Articles

Herbicide safener isoxadifen-ethyl associated with increased Goss's wilt severity in corn (Zea mays).

Goss's bacterial wilt and leaf blight (Goss's wilt), caused by the bacterium Clavibacter nebraskensis, is a corn disease that has been a top ten yield-reducing disease in North America in the past 15 years. Isoxadifen-ethyl is an herbicide safener that effectively increases cytochrome P450 activity in corn which enhances a plant's metabolism of herbicide molecules. Recent research found a potential link between isoxadifen-ethyl and increased Goss's wilt severity. The application of isoxadifen-ethyl increased (P = 0.014-0.046) area under disease progress curve (AUDPC) by 19%, 7%, and 9% at three environments, independent of accompanying herbicide or herbicide application timing. However, no significant differences in incidence of systemic wilt or corn grain yield occurred among treatments at any environment. These data provide evidence for an association between isoxadifen-ethyl safener and Goss's wilt in corn. The reason for this association is unknown, but the safener may affect plant or pathogen physiological mechanisms. While the increased disease severity did not result in decreased grain yield in these experiments, an increase in pathogen inoculum due to higher disease severity could influence Goss' wilt epidemics in future years. © 2024 Society of Chemical Industry.

Planting date and dicamba‐based herbicide programs influence soybean production in the Southern Great Plains

AbstractThe interplay of management decisions involving soybean (Glycine max L.) planting date, herbicide programs, and herbicide application timings is critical to optimize soybean performance and weed control in Southern Great Plains soybean production systems. This research sought to evaluate soybean yield potential and the level of weed control as influenced by early‐, delayed‐, and late‐ planting dates and various combinations of preemergence (PRE), early‐postemergence (EPOST), and mid‐postemergence (MPOST) weed management programs. A field study was established in Bixby, OK in 2017 and 2018 under irrigated conditions and in Perkins, OK in 2017 under dryland conditions, consisting of three planting windows (early, delayed, and late) of XtendFlex soybean, with or without a PRE (chlorimuron + flumioxazin + pyroxasulfone + glyphosate + dicamba) combined with EPOST or EPOST + MPOST (glyphosate + dicamba) versus no in‐season applications. The gap in late‐planted soybean yield potential, compared to early‐planted soybean, was exacerbated in the dryland systems (1346 kg ha−1) versus an irrigated system (2311 kg ha−1). Use of PRE provided 60% weed control until MPOST and increased yields by 657 kg ha−1 and 457 kg ha−1 for delayed and late‐planted soybean, respectively. Late‐planted soybean with EPOST + MPOST provided up to 50% weed control, but lack of biomass production for cultural control reduced weed control by 29% compared to early‐ and delayed‐planted soybean. From an agronomic management standpoint, the time of soybean planting is influential on the success of weed control measures and soybean yields in double‐cropping system in the Southern Great Plains, particularly with late‐planted soybean.

Italian Ryegrass (Lolium perenne L.) Control in Durum Wheat (Triticum Durum L.) As Affected by Herbicide Application Timing and the Addition of Mineral Oil

Italian Ryegrass (Lolium perenne L.) Control in Durum Wheat (Triticum Durum L.) As Affected by Herbicide Application Timing and the Addition of Mineral Oil

Analyzing the synergistic impact of UAV-based technology and knapsack sprayer on weed management, yield-contributing traits, and yield in wheat (Triticum aestivum L.) for enhanced agricultural operations

Modern agriculture uses agrochemicals to boost crop yield and quality. Using knapsack sprayers, Indian farmers apply herbicides, insecticides, and other chemicals. Herbicides are applied by manually operated knapsack sprayers, which are laborious, uneven, and prone to human mistakes. Unmanned aerial vehicles (UAVs) are a promising agricultural spraying alternative to manual operations. Future agricultural and field scouting technology aids weed management, pest control, and automated irrigation systems. Drone herbicide spraying was compared to traditional and mechanical knapsack sprayers in this study. The study also tested knapsack (manual) and UAV herbicide pre- and post-emergence and spraying on wheat crops. Herbicide application by knapsack and drones was examined for weed control, yield-contributing characters, and wheat yield. The experiments were performed at Vasantrao Naik Marathwada Krishi Vidyapeeth's Department of Agronomy in Parbhani, Maharashtra. A randomized block design (RBD) with eight treatments, including drones and knapsack sprayers for weed management in wheat crops with different herbicide application times and repeated hoeings (cultural method), was compared to absolute weed-free, where no weeds were allowed to grow in wheat by frequent weeding and weedy inspection. The experimental field measured 7.2 m x 6 m gross land area and 6.3 m x 5.6 m net land area. When winds were light, the drone was flown at 3 m to avoid herbicide droplets drifting. The study found that unweeded wheat yields dropped 38 % owing to weed insects. The pre-emergence (PE) application using a knapsack sprayer and post-emergence (POE) herbicide application via a drone synergistically resulted in the highest growth and yield for T3, attaining values of 11.02 gm/plant, an average of 284.97 grains/plant, and a per-hectare grain yield of 4256.59 kg/ha. The cultural approach of weed management (T4) reduced yield by 21.2 %; however, treatment T3 improved yield contributing characteristics and losses by just 2.8 %. UAV-based herbicide spraying is a fast and easy method that contributes to achieving sustainable development goal (SDG) 2 for Zero Hunger by promoting sustainable plant protection and crop production.

Palmer Amaranth (Amaranthus palmeri) Control in Dicamba-Tolerant Cotton (Gossypium hirsutum) when Applied with Various Dicamba + Insecticide Tank-Mixtures

Postemergence herbicide application timings for Palmer amaranth (Amaranthus palmeri) often coincide with foliar insecticide applications in cotton (Gossypium hirsutum). Combining multiple pesticides into a single application increases efficiency while reducing overall application cost. Multiple foliar insecticides are now labeled for dicamba tank-mixes. However, there is limited literature with respect to efficacy of dicamba on Palmer amaranth control when applied with insecticides. Field experiments were conducted from 2018 to 2020 to evaluate the effect of carrier volume and insecticide on the efficacy of dicamba (XtendiMaxTM with VaporGripTM) to control Palmer amaranth in XtendFlex™ cotton production systems. Dicamba was tank-mixed with acephate and dimethoate to four-leaf cotton and with thiamethoxam and sulfoxaflor just prior to bloom. Applications were made at carrier volumes of 140 and 280 L ha-1 and with a single spray droplet size of 800 µm. Palmer amaranth control 7 d after treatment was negatively impacted when applications included dimethoate; however, no corresponding response in seedcotton yield was observed relative to dicamba applied alone. However, when pooled over carrier volume, applications containing dicamba + acephate resulted in higher seedcotton yield than applications of dicamba + dimethoate. Additionally, pre-bloom applications of dicamba + thiamethoxam or sulfoxaflor increased Palmer amaranth efficacy relative to dicamba applied alone. Although certain insecticides are known to increase herbicidal crop response, the impact of insecticides on herbicide efficacy to control specific weed species is largely unknown. Therefore, we conclude that multiple dicamba + acephate, thiamethoxam, or sulfoxaflor tank-mixtures provide similar control of Palmer amaranth compared to dicamba alone.

Characterising Productivity Factors Affecting Maize (Zea mays) Production in a Smallholder Crop-Livestock System

Socio-economic factors can influence decisions and the intensity of management practices, which when appropriately considered could bridge yield gaps. The study aimed to investigate factors affecting maize (Zea mays L.) production in a smallholder crop-livestock system. Social and management analyses were performed to ascertain the factors influencing maize productivity using interviews and questionnaires. The study was conducted in two main maize-producing regions of Eswatini, the Highveld at Mankayane and Middleveld at Luve. Additionally, on-farm trials were established for two cropping seasons to evaluate maize response to three fertiliser regimes: cattle manure only, cattle manure plus inorganic fertiliser, and inorganic fertiliser only and lastly to determine the most economic fertiliser regime. Each fertiliser regime was replicated six times. Weed biomass and maize yield were collected from a 5 m × 1 m quadrat. Moreover, economic analysis for each fertiliser regime was performed using partial budgets comprising fertiliser and weed management costs. The social and management analyses showed that maize yield was strongly associated with household size (p < 0.05), land area cultivated (p < 0.05) and herbicide application timing (p < 0.05) indicating the effect of these factors on yield. On-farm trials revealed that the inorganic fertiliser only regime resulted in a significantly (p < 0.05) higher maize yield compared to manure only and manure plus inorganic fertiliser regimes in both study areas. Weed biomass was significantly (p < 0.05) lower in the inorganic fertiliser only regime at Mankayane compared to the manure only and manure plus inorganic fertiliser at both localities. The economic analysis showed that the manure only fertiliser regime had low costs that vary and high net benefits indicating that manure has the potential to improve soil conditions, reduce environmental impacts, and increase profits.

Impact of soil residual auxin herbicide on seedling emergence and biomass differs between soil types, water pulse event, and seedling species

Synthetic‐auxin herbicides are often used to control woody plants and aid in grassland restoration. Seed‐based restoration is common alongside herbicide applications and there may be unintended effects of these herbicides on dryland plants at the seed and seedling stages. Additionally, abiotic conditions at the time of herbicide application may influence herbicide–soil–plant interactions. We conducted a greenhouse study to examine the effects of a common shrub‐control herbicide mix and its interaction with soil type and a post‐herbicide water pulse on common desert plant seeds and seedlings. In this greenhouse study, we found that a subset of species responded negatively to soil residual herbicide activity of a mixture of aminopyralid, clopyralid, and triclopyr at the seed and seedling stages. Species sensitive to soil herbicide residues were primarily shrub and forb species that are often the target species of herbicide applications for woody plant control, such as honey mesquite (Prosopis glandulosa) and creosote bush (Larrea tridentata). However, two shrub species (four‐wing saltbush [Atriplex canescens], soaptree yucca [Yucca elata]) and one perennial grass species (Arizona cottontop [Digitaria californica]), which are used in dryland restoration projects, were found to be particularly sensitive to soil residual herbicide activity. Thus, if using these herbicides to control woody plants and restore herbaceous vegetation via active seeding or relying on the in situ seed bank, considerations should be given to what species are used in the seed mix, what species are already present in the soil seed bank, and other details of the circumstances of herbicide application.

Does narrow row spacing suppress weeds and increase yields in corn and soybean? A meta-analysis

AbstractNarrow row spacing (&lt;76 cm) could improve crop competitiveness, suppress weeds and might provide yield advantage. Many studies have been conducted to evaluate the impact of narrow row spacing; however, no quantitative synthesis of these studies exists. The objectives of this meta-analysis were to (1) quantify the overall effect of narrow row spacing (&lt;76 cm) on weed density, biomass, control, weed seed production, and yield in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] compared with 76-cm row spacing, and (2) assess the influence of agronomic management decisions (tillage type, weed management, herbicide application frequency and time) on effect of narrow row spacing on weed suppression and corn and soybean yield. We compiled 1,904 pair-wise observations from 35 studies conducted in 12 states in the United States during 1961 to 2018. Averaged across individual observations, narrow row spacing suppressed weed density by 34%, weed biomass by 55%, and weed seed production by 45%, while it improved weed control by 32% and crop yield by 11% compared with 76-cm row spacing. Narrow row spacing in soybean suppressed weed density by 42%, weed biomass by 71%, and increased crop yield by 12% compared with 76-cm row spacing. Although narrow row spacing had a nonsignificant effect on response variables in corn, the number of studies (n = 1 to 6) and observations (n = 1 to 59) addressing each response variable were limited. Tillage type (conventional and reduced) did not influence the response of weed density, control, and seed production in narrow row spacing; however, weed biomass and weed seed production were more greatly reduced with the sequential application of herbicides compared with a single application. Thus, narrow row spacing in soybean can be integrated with other options for management of herbicide-resistant weeds.

Russian thistle (Salsola tragus) postharvest control and plant dispersal

AbstractRussian thistle is one of the most important broadleaf weeds in the semiarid U.S. Pacific Northwest. It consumes soil water after wheat harvest, compromising the yield of the following crop. The objectives of this work were to determine the impact of post–wheat harvest herbicide application timing on Russian thistle control and of stubble height on Russian thistle postharvest control and plant dispersal. For the first objective, experiments were conducted at the Columbia Basin Agricultural Research Center, Adams, OR (CBARC), and the Lind Dryland Research Station, Lind, WA (LDRS), in 2020 and 2021. Herbicides evaluated included paraquat, glyphosate, and either bromoxynil + pyrasulfotole (CBARC) or bromoxynil + metribuzin (LDRS). The different post–wheat harvest application timings were 24 h and 1, 2, and 3 wk after harvest. For the second objective, two stubble heights (short and tall) were compared for their impact on control at CBARC and in a production field near Ione, OR. Paraquat provided the greatest control in all scenarios, with no differences in application timings or stubble height. Impacts of application timings were not clear for glyphosate or bromoxynil mixtures. For glyphosate treatments, control in short stubble was 11% greater than in tall stubble in both years. Control was also greater in short stubble for the bromoxynil + pyrasulfotole application in 2020. However, Russian thistle plant dispersal was greater in short stubble at both locations. At CBARC, plant dispersal in short stubble was 58%, compared to 18% in tall stubble. Near Ione, plant dispersal in flattened stubble was 88%, compared to 43% in nonflattened short stubble. Leaving tall stubble at harvest should be considered to reduce Russian thistle plant dispersal if the infestation is going to be left untreated after harvest; otherwise, short stubble might result in better Russian thistle control when using systemic herbicides, such as glyphosate.

Cereal rye residue management tactics influence interrow and intrarow weed recruitment dynamics in field corn when planting green

AbstractDelaying cover crop termination until cash crop planting (i.e., planting green) is an emerging no-till practice. Improved management recommendations are needed for optimizing weed suppression benefits while minimizing other pest, fertility, and crop management risks when planting green in corn production systems. In a 2-yr field experiment, we evaluated the interaction between cereal rye residue management tactics (standing residue, roll-crimping, roll-crimping with row cleaners) and herbicide programs (1-pass preemergence [PRE], 2-pass postemergence [POST]) when planting green on weed recruitment spatial patterns and corn performance compared to standard termination (14 d preplant [DPP]) and ryelage harvest (14 DPP) practices. In a 2-yr on-farm experiment, we evaluated corn performance in response to the same residue management tactics. Cereal rye biomass production varied significantly across years in on-station experiments, with average (4.9 Mg ha−1) and anomalous (9.9 Mg ha−1) levels observed in 2020 and 2021, respectively. In 2020, planting green with an integrated roll-crimper/row cleaner system resulted in greater intrarow weed density compared with planting green into standing cereal rye. Interrow weed density was lower when roll-crimping was employed compared to early termination (14 DPP). Planting green into standing cereal rye resulted in greater mean corn height (V5 stage) compared to other treatments, but corn population and yield did not differ. In 2021, few differences in weed recruitment patterns were observed, but corn population and yield were significantly lower in planting green treatments compared to early termination. In both years, late-season weed biomass was lower in two-pass POST programs compared to one-pass PRE programs. On-farm trials showed that planting green into standing residue increases corn height and can reduce corn populations, which may lead to reduce yields. Our results suggest that management recommendations for optimizing herbicide application timing should consider intrarow and interrow weed recruitment dynamics associated with residue management tactics needed to optimize corn performance.

Chemical Site Preparation Mixtures, Application Timing, and Herbaceous Weed Control Impacts on Loblolly Pine Development Through Six Years

Abstract Chemical site preparation is a critical management practice for southern pine plantation establishment. Imazapyr and ester triclopyr are frequently used for chemical site preparation in the Lower Coastal Plain to control waxy leaf shrub species, yet limited information is available on optimal imazapyr and triclopyr tank mixes and individual herbicide application timing(s) to achieve maximum loblolly pine (Pinus taeda L.) growth. The objectives of this study were to determine the survival, growth, and stem defect response of 6-year-old loblolly pine to four chemical site preparation treatments plus an untreated control, three application timings, and first year herbaceous weed control (hwc) on a poorly drained flatwoods site. Treatments included two imazapyr and triclopyr rates applied as tank mixes, triclopyr and imazapyr alone, and an untreated control with hwc applied to half of each treatment plot. Results showed no treatment had superior survival or growth, whereas September-applied imazapyr and triclopyr tank mixes tended to result in improved growth. Triclopyr alone along with first year, banded hwc resulted in similar growth to imazapyr and triclopyr tank mixes. First-year hwc significantly enhanced survival and growth. Stem defects were more common in the chemical site preparation treatments than the control. Study Implications: Age-6-year results from this study indicate that loblolly pine (Pinus taeda L.) growth following application of chemical site preparation tank mixes containing imazapyr and triclopyr applied during September or October tended to be superior to July applications. Triclopyr applied alone with first growing season herbaceous weed control (hwc) may offer satisfactory near- and long-term loblolly pine growth as imazapyr and triclopyr tank mixtures on sites with similar competing vegetation. These findings may allow for less herbicide use on sites previously managed for pine production and show the importance of first year hwc for Coastal Plain flatwoods sites.

Seed production potential of Medicago denticulata in relation to growth stage at the time of herbicide application

Seed production potential of Medicago denticulata in relation to growth stage at the time of herbicide application

Cover crops and preemergence herbicides: An integrated approach for weed management in corn-soybean systems in the US Midwest

Adoption of a fall established, high biomass cereal rye cover crop has potential to diversify weed management in corn and soybean production systems, reducing the selection pressure for resistance to postemergence herbicides. However, farmers and crop consultants express concern about limited weed suppression from an overwintering cover crop in areas where high biomass production is limited by cooler spring temperatures, such as in the Upper-Midwest U.S. Use of a preemergence herbicide, regardless of cover crop adoption, is a standard recommendation for improving early season weed control in corn and soybean. Field experiments were conducted at two sites in Wisconsin to assess the effects of six soil management practices (tillage, no-till, and four cereal rye cover crop termination timings/methods) with or without the use of a preemergence herbicide on weed suppression at the time of postemergence herbicide application and crop productivity. Results showed that cereal rye biomass increased &amp;gt; 6x between termination at the time of cash crop planting versus termination two weeks later. In corn and soybean, weed ground cover was lower for soil management with cereal rye cover crop terminated two weeks after cash crop planting (≤ 7% weed cover) compared to all other soil management practices (≥ 23% weed cover) when a preemergence herbicide was not used. Use of a preemergence herbicide resulted in low weed ground cover across treatments in corn (≤ 7% weed cover) and soybean (≤ 13% weed cover). Corn and soybean yield was not affected by preemergence herbicide treatments. Corn yield was lower at the south-central Wisconsin location for the soil management with a cereal rye cover crop terminated two weeks after cash crop planting (9.82 Mg ha-1) compared to all other soil management practices (≥ 12.07 Mg ha-1); at the southwest Wisconsin location, corn yield was greater for the conventional tillage treatment (14.28 Mg ha-1) compared to all other soil management treatments (≤ 10.89 Mg ha-1). Soil management did not affect soybean yield, although yields were different between locations with 3.44 Mg ha-1 at the south-central Wisconsin compared to 4.77 Mg ha-1 at the southwest Wisconsin location. These results indicate that in the absence of a high biomass cereal rye cover crop, preemergence herbicides are important for in-season weed control. Also, the inclusion of a late-terminated cereal rye cover crop in soybean should be considered as an effective management practice for reducing weed ground cover without affecting crop yield.

Quantifying the germination response of Parthenium hysterophorus at various temperatures and water potentials by using population-based threshold model.

Predicting the germination behavior of parthenium weed against different conditions of temperature and osmotic stress is helpful for studying the growth and development history of parthenium in different ecological contexts. Sustainable weed control strategies based on population-based threshold (PBT) models are profitable tools for crop planting date, herbicide application, and tillage operation time. To predict the emergence of parthenium by using thermal time (TT), hydrotime (HT), and hydrothermal time (HTT) analyses, seeds were exposed to varying constant temperatures (5, 10, 15, 20, 25, 30, 35, and 40°C) and water potentials (− 0.25, − 0.5, − 0.75, and − 1.0 MPa) under a controlled environment. Parthenium seeds showed better responses in terms of higher germination percentage and lower germination time at 20 and 25°C. The use of the germination modeling approach proposed the base temperature (7.2°C), optimum temperature (20°C), and ceiling temperature (42.8°C) for this weed. Moreover, germination behavior was also studied at different water potentials under different temperature regimes (10, 20, and 30°C). The HTT model predicted higher germination percentages (82.8 and 54.8%) of parthenium seeds at water potentials from 0 to −0.25 MPa, respectively, under a temperature of 20°C, and also identified a base water potential (Ψb(50) of − 0.54 MPa for germination. In conclusion, the use of the HTT modeling approach is helpful for predicting the emergence response of parthenium in a changing climate and ultimately supportive in time scheduling of parthenium weed management in cropping systems.

Approach to Demography of ALS-Resistant Glebionis coronaria as Influenced by Management Factors: Tillage, Allelopathic Crops and Herbicides

Glebionis coronaria (L.) Cass. ex Spach is one of the most serious weeds in cereal crops in Northern Tunisia. Our previous studies have confirmed the presence of resistance to ALS-inhibiting herbicides in G. coronaria, showing the evolution of cross-resistance through TS and NTS mechanisms. The purpose of this study was to evaluate the effects of (i) two tillage practices (conventional tillage and reduced tillage), (ii) three known allelopathic crops: Hordeum vulgare L. (Barley), Brassica napus L. (Rapeseed) and Triticum durum (Wheat) and (iii) herbicides belonging to different modes of action on the density, the cohort numbers and the growth of an ALS-inhibiting cross-resistant population of G. coronaria. Field experiments were conducted in two consecutive years (2017–2018 and 2018–2019) in the Fritissa-Mateur-Bizerte region. Our results revealed that barley considerably contributed to the decrease in G. coronaria’s density, cohort number, total biomass accumulation and plant height. The effect of rapeseed is likely dependent on the tillage practice and the timing of herbicide application, while G. coronaria could be successfully controlled in wheat using auxin herbicides. It is suggested that the management of resistant population of G. coronaria could be achieved by combining barely or rapeseed with right tillage practice and auxin herbicides’ application.

Soybean yield loss from delayed postemergence herbicide application based on weed height, days after emergence, accumulated crop heat units, and soybean growth stage

AbstractLimited information exists on the critical time of weed removal (CTWR) with the currently used soybean cultivars in Ontario. A study consisting of eight field experiments was conducted from 2017 to 2019 in Ontario, Canada, to determine the impact of delayed postemergence (POST) herbicide application on soybean yield based on average weed height at application, days after crop emergence (DAE), accumulated crop heat units (CHU) from the date of planting, and soybean growth stage. The regression model estimated the weed size at herbicide application that led to 1%, 2.5%, and 5% yield loss in soybean was 9, 14, and 20 cm under low weed density (averaging 73 to 134 plants m−2) and 3, 4, and 6 cm under high weed density (143 to 153 plants m−2) conditions, respectively. The estimated DAE at herbicide application time that led to 2.5%, 5%, 10%, and 25% yield loss in soybean was 24, 30, 37, and 53 DAE under low weed density and 8, 10, 14, and 23 DAE under high weed density, respectively. The predicted crop stage at herbicide application that resulted in 2.5%, 5%, 10%, and 25% yield loss in soybean was V4, V5, R2, and R5 under low weed density and VE, VC, V1, and V4 under high weed density, respectively. This study concludes that soybean yield loss is influenced by the weed density (low vs/high) and the time of the first POST herbicide application. When the first POST herbicide application was delayed until soybean was at the V2 stage the monetary loss was Can$20.46 and Can$221.20 ha−1 in low and high weed-density environments, respectively.

Impact of delayed postemergence herbicide application on corn yield based on weed height, days after emergence, accumulated crop heat units, and corn growth stage

AbstractNine field experiments were conducted from 2017 to 2019 in Ontario to determine the impact of early weed interference on corn yield based on corn growth stage, days after emergence (DAE), accumulated crop heat units (CHU), and weed size. The predicted weed size at herbicide application that resulted in a 1%, 2.5%, 5%, 10%, 25%, and 50% yield loss in corn was estimated to be 1, 4, 11, 53, non-estimable (N est.*), and N est.* cm under low weed density and 3, 5, 7, 11, 27, and N est.* cm under high weed density, respectively. The predicted DAE at herbicide application time that resulted in a 1%, 2.5%, 5%, 10%, 25%, and 50% yield loss in corn was predicted to be 14, 20, 27, 44, N est.*, and N est.* DAE under low weed density and 5, 7, 11, 17, 25, and 59 DAE under high weed density, respectively. The predicted CHU from planting at herbicide application time that led to a 1%, 2.5%, 5%, 10%, 25%, and 50% yield loss in corn was 468, 636, 821, 1,271, N est.*, and N est.* CHU from planting under low weed density and 207, 283, 385, 551, 972, and 1,748 CHU from planting under high weed density, respectively. The predicted crop stage at herbicide application that led to a 1%, 2.5%, 5%, 10%, 25%, and 50% yield loss in corn was V5, V6, V7, V11, N est.*, and N est.* under low weed density and V1, V2, V3, V4, V8, and V14 under high weed density, respectively. Results indicate that weeds must be controlled before they reach 7 cm in height, prior to 11 d after crop emergence, prior to 385 accumulated CHU from emergence, or prior to the V3 stage under high weed density to avoid greater than 5% yield loss.

Effect of the Time of Herbicide Application and the Properties of the Spray Solution on the Efficacy of Weed Control in Maize (Zea mays L.) Cultivation

A field experiment was carried out in 2019–2021. The effect of an increased amount of iron in water and the addition of citric acid on the efficacy of herbicides applied in maize cultivation at various times was tested. In the pre-emergence treatment, thiencarbazone-methyl + isoxaflutole were applied, while in the post-emergence treatment, nicosulfuron + tritosulfuron + dicamba were applied once in a full dose or in low dose system at two times in half of the recommended dose with the addition of an adjuvant. In selected combinations, FeSO4 × 7H2O and citric acid were added to the composition of the spray solution. The species composition of weeds and the efficacy of the herbicides used were determined. Plant stress caused by competition from weeds was investigated by measuring the plant chlorophyll fluorescence. The height of the cultivated plants and their yield level were also determined. The lowest efficacy of weed control was observed when the post-emergence herbicides were applied once. Increasing the iron content in water reduced the efficacy of the herbicides, but the addition of citric acid made it possible to decrease this problem.

Application timing of herbicides, glyphosate and atrazine, sway respective epidemics of foliar pathogens in herbicide‐tolerant rapeseed

AbstractRapeseed (Brassica napus) production in Australia relies heavily on triazine‐or glyphosate‐tolerant cultivars. For 14 triazine‐tolerant cultivars, disease development of Neopseudocercosporella capsellae (white leaf spot), Alternaria brassicae and A. japonica (Alternaria leaf spot), and Hyaloperonospora brassicae (downy mildew) were all dependent upon herbicide application timing (p &lt; 0.001), with significant differences between cultivars (p &lt; 0.001) and a significant interaction (p &lt; 0.001) between herbicide application timing and cultivars. Atrazine applied preinfection by N. capsellae, A. brassicae, or A. japonica enhanced disease incidence, severity, and leaf collapse, while atrazine application postinfection for these same pathogens reduced all three disease parameters. However, for H. brassicae, application of atrazine after, and especially prior to, infection resulted in lower disease incidence, severity, and leaf collapse. Application of glyphosate on five glyphosate‐tolerant cultivars for N. capsellae resulted in significant differences (p &lt; 0.05) between glyphosate application treatments, and between host cultivars in terms of incidence and consequent leaf collapse. For A. brassicae, A. japonica, and H. brassicae, glyphosate resulted in significant differences (p &lt; 0.001) across application timings between cultivars, and a significant interaction (p &lt; 0.001) between herbicide application timings and cultivars. Glyphosate applied on glyphosate‐resistant rapeseed after, and especially prior to, attack by H. brassicae, reduced downy mildew. These are the first studies to highlight how the timing of application of triazine or glyphosate in relation to pathogen infection is critical to the susceptibility of rapeseed to white leaf spot, Alternaria leaf spot, and downy mildew. This new understanding offers fresh possibilities for improved management of these diseases in herbicide‐tolerant rapeseed crops.

Influence of time of day on dicamba and glyphosate efficacy

AbstractRenewed interest in studying auxin herbicides (WSSA Group 4) is increasing as a result of the release of genetically engineered crop varieties that are tolerant to preemergence and postemergence applications of specific formulations of dicamba. Auxin-resistant crops were developed in response to the development of weed species resistant to glyphosate and other herbicides. Research was conducted at multiple field locations in Georgia in 2018 and 2019 to examine weed control when postemergence herbicides were applied to dicamba- and glyphosate-resistant cotton at eight different points in time over a 24-h period. Applications were made at 1 h prior to sunrise all the way up to midnight during the same day to examine the effect of herbicide application timing on broadleaf weed control. Glyphosate, dicamba, and glyphosate plus dicamba were applied at each timing. Visual ratings of weed control were scored at 7, 14, 21, and 28 d after treatment (DAT). Weed control was affected by herbicide application timing. Midnight applications resulted in the lowest levels of control. Sicklepod, pitted morningglory, and prickly sida control was 49%, 38%, and 41%, respectively. Greatest control of all three species (up to 99%) occurred from the noon to 1 h prior to sunset application timings. Orthogonal contrasts of timing of application indicated that weed control was improved with day &gt; night and pre-dawn &gt; midnight.