Efficacy Of Pre-emergence Herbicides Research Articles

Efficacy of pyroxasulfone and its combinations against weeds in wheat (Triticum aestivum)

A field experiment was conducted during the winter (rabi) season of 2021–22 at the research farm of Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur, Madhya Pradesh to study the efficacy of pre-emergence herbicides against weeds in wheat (Triticum aestivum L.). The experiment was laid out in a randomized block design with 3 replications and 8 weed control treatments. Major weed flora in the experimental site, viz. Medicago polymorpha (L.) (28.97%) and Cichorium intybus (L.) (26.19%) were predominant in dicot weeds and in monocot weeds, Phalaris minor (17.82%) was dominant. The weedy check plot had the higher density and dry weight of weeds. Hand weeding (once) was done at 25 DAS (day after sowing) in wheat, reducing weeds density and dry weight to the maximum extent at 40 DAS with a weed control efficiency (WCE) of 92.8%, proving superiority over other treatments. Among the herbicidal applications, pyroxasulfone + metribuzin at 127.5 + 280 g a.i./ha significantly reduced the monocot and dicot weeds density and dry weight, followed by pendimethalin + pyroxasulfone at 1250 + 127.5 g a.i./ha. Pyroxasulfone + metribuzin at 127.5 + 280 g a.i./ha resulted in maximum values of growth parameters, viz. plant height (66.38 cm), number of tillers/m2 (403.14) and yield attributing characters, viz. grains per earhead (51.00) and grain yield (5.65 t/ha) as compared to other herbicidal treatments.

Productivity of Finger Millet (Eleusine coracana (L) Geartn) as Influenced by Pre-emergence Herbicides in the Northern Guinea savanna of Nigeria

Two field trials were conducted during 2011 and 2012 wet seasons at the Research Farm of the Institute for Agricultural Research, Ahmadu Bello University, Samaru Zaria (Lat. 11 o 11 1 N, Long. 07 O 38E and 686m above sea level), in the northern Guinea savannah zone of Nigeria, to evaluate the efficacy of pre-emergence herbicides on weed in finger millet. The treatments were atrazine (80WP) at the rates of (0.4, 0.8, 1.2 and 1.6 kg a.i/ha), RafT ® (500SC ) (Atrazine 250 g/l + Terbuthylazine 250 g/l ) at the rates of (0.25, 0.5, 0.75, and 1.0 kg a.i/ha) and Bullet (R) (700SC) (Atrazine 225 g/l + Terbuthylazine 225 g/l + Acetochlor 250 g/l) at the rates of (0.35, 0.75, 1.05 and 1.4 kg a.i/ha), hoe weeded control at 3 and 6 WAS and a weedy check. The treatments were laid out in a Randomized Complete Block Design (RCBD), replicated 3 times. The result shows that all the herbicide treatments significantly reduced weed dry weight than the weedy check. Application of atrazine at 0.8 kg a.i/ha or Raft at 0.5 kg a.i/ha gave lower weed dry weight and weed cover score than the hoe weeded control at 3 and 6WAS.While all the rates of Bullet, Raft at 0.75 and 0.1 kg a.i./ha and atrazine at 1.2 and 1.6 kg a.i./ha resulted in lower weed dry matter production which were comparable to hoe weeded control at 3 and 6WAS. Based on the results obtained from this study, 0.8 kg a.i./ha atrazine or 0.5 kg a.i./ha Raft gave season long weed control over hoe weeded check in finger millet with yield increase of 94.2 and 99.5%, respectively. The weedy checks reduced yield of finger millet by 66.7%.

Pre-emergence control and interference of voluntary maize plants on a soybean crop in Brazilian Cerrado

The succession of soybean/maize has been largely adopted. Storm damage and crop problems can lead to grain loss, generating maize ear fragments or even whole ears that remain in the soil and still display germination viability, resulting in the occurrence of volunteer plants. In this context, the present study aimed to evaluate the interference of voluntary maize plants on soybean and investigate the susceptibility of maize hybrids to pre-emergence herbicides. In the first step, an experiment was performed evaluating the influence of voluntary maize plant density and spatial distribution on soybean. The experiment was performed in a randomized completely block design (RCBD) with four replications, with treatments disposed in factorial arrangement (2 x 4) + 1. The first factor corresponded to the spatial distribution of maize plants: row or in between soybean rows; while the second factor adopted four infestation densities of maize plants m-2: 4, 8, 12, and 16. The additional treatment consisted of a control without maize plants. For the second step, an experiment was conducted in two locations aiming to determine the efficacy of pre-emergence herbicides in the control of voluntary maize. Both experiments were installed in RCBD in a split-plot scheme with four replications. Fomesafen, lactofen, sulfentrazone, chlorimuron-ethyl, diclosulam, flumetsulam, imazethapyr, clomazone, metribuzin, [sulfentrazone + diuron], [imazethapyr + flumioxazin], and a control without herbicide application were evaluated in the main plot. In each subplot, the maize hybrids DKB310 PRO3™ and DKB390 PRO3™ were evaluated. No influence on the position of voluntary maize on the soybean yield was observed. The presence of the maize population led to a progressive decrease in soybean yield, ranging up to 86%, at 16 plants m-2. DKB390 displayed a stand reduction of 82.88% after the use of diclosulam. Diclosulam led to better results regarding maize plant decreases for both hybrids.

Weed dynamics, crop growth and yield attributes of irrigated chickpea in response to chemical weed control

Weeds in chickpea fields cause severe yield losses. Field experiments were undertaken in winter 2017–2018 and 2018–2019 to assess the efficacy of pre-emergence (PRE) and post-emergence (POST) herbicides in irrigated chickpea. PRE herbicides, viz. pendimethalin (as emulsifiable concentrate and capsulated suspension), s-metolachlor, and pendimethalin + S-metolachlor were used in two varieties of chickpea, viz. Bhakkar-2011 (Desi) and Noor-2013 (Kabuli). POST herbicides, viz. Lactofen, haloxyfop, quizalofop, and clodinafop-propargyl were applied at 30 days after sowing. Weed free and weedy check plots were maintained. Efficacy of PRE herbicides was better than POST herbicides, especially in the plots of Desi chickpea. All PRE herbicides were similar in suppressing weed dry biomass. Haloxyfop, quizalofop, and clodinafop-propargyl showed poor control of grass weeds. Irrespective of chickpea genotype, the maximum seed yield (1.16 and 1.30 Mg ha−1 in 2017–2018 and 2018–2019, respectively) was recorded for the weed free plots, with yield advantage of 137% over control. No herbicide provided season-long weed control. The huge gap between yields of weed free and herbicide-treated plots showed the need of integration of other weed management strategies in this crop.

Crop residue and rainfall timing effect on pre-emergence herbicides efficacy using different spray nozzle types

Weed control success with pre-emergence (PRE) herbicides is affected by environmental factors including rainfall and plant residue. Two greenhouse experiments were conducted to evaluate PRE herbicide efficacy against johnsongrass [Sorghum halepense (L.) Pers.], prickly sida (Sida spinosa L.) and velvetleaf (Abutilon theophrasti Medik.). One experiment investigated herbicide efficacy under two crop residue amounts (2500 and 5000 kg ha−1) and the second examined herbicide efficacy influenced by simulated rain at two, four, and eight days after application (DAA). Five herbicides (pendimethalin, metribuzin, clomazone, imazethapyr and pyroxasulfone) and four nozzles types (XR, ULD, TTI and TTI60) were used. Nozzle type did not affect weed control across residue levels. Pendimethalin better controlled S. halepense under the low residue level. Imazethapyr efficacy for S. spinosa and A. theophrasti increased under high residue level. Imazethapyr applications for S. spinosa and A. theophrasti control were more effective when sprayed with the TTI nozzle regardless of rainfall timing. Longer periods without rain after application improved pendimethalin efficacy against S. spinosa and A. theophrasti, while pyroxasulfone better controlled S. spinosa with rain two DAA. Metribuzin and clomazone provided the best weed control among herbicides for all residue levels and rainfall scenarios.

Bazı Toprak Herbisitlerinin Domates Fidelerini Şaşırtmadan Önce Yabancı Otları Kontrol Etme Potansiyeli

Weeds reduce yield competing with the tomato for nutrients, water, and light. Also, some common broadleaf weeds such as nightshade, cocklebur, and pigweed are hosts to bugs, disease, and viruses. Weed control with herbicides is focused directly or indirectly on improving the competitive ability of the crop with regard to the weeds. A field study was performed to investigate pre-plant and pre-emergence herbicide's efficacy on weeds and tomato cv. Alsancak Fı at vegetable research fields of Department of Horticulture in Siirt University, in June-August 2016-17. Oxyfluorfen (480 g/l a.i ha–1) active ingredient was identified as promising active ingredient because Weed Control Efficiency (WCE) was found 86% at 14 DAT, 79% at 28 DAT, 65% at 42 DAT, 56 DAT 52%, also Weed Index (WI) was detected 29%. All weed control processes have effectively reduced the density of weeds. However, clomazone (480 g/l EC 0.2 L a.i ha-1), fluometuron (500 g/l SC 2 L a.i ha-1), and flurochloridone (250 g/l EC 2.5 L a.i ha-1) were extremely injured the tomatoes. Although these there active ingredient control weeds more effectively, it cannot be used for weed control in tomato fields because of excessive crop injury. Oxyfluorfen 240 g/l EC 1 L a.i ha-1 and pendimetalin 450 g/l CS 3 L i ha-1 were found relatively promising, these two can be used, but the risk of phytotoxicity depending on application period, climatic and soil conditions should not be ignored.

Glyphosate Resistance Confirmation and Field Management of Red Brome (Bromus rubens L.) in Perennial Crops Grown in Southern Spain

The excessive use of the herbicide glyphosate on annual and perennial crops grown in Southern Spain has caused an increase in resistant weed populations. Bromus rubens has begun to spread through olive and almond cultivars due to low glyphosate control over these species, whereas previously it had been well controlled with field dose (1080 g ae ha−1). Characterization using Simple Sequence Repeat (SSR) markers confirmed the presence of B. rubens collected in Andalusia. A rapid shikimic acid accumulation screening showed 17 resistant (R) populations with values between 300 and 700 µg shikimate g−1 fresh weight and three susceptible (S) populations with values between 1200 and 1700 µg shikimate g−1 fresh weight. In dose–response experiments the GR50 values agreed with previous results and the resistance factors (RFs: GR50 R/GR50 S (Br1)) were between 4.35 (Br9) and 7.61 (Br19). Foliar retention assays shown no differences in glyphosate retention in both R and S populations. The tests carried out in a resistant field (Br10) demonstrated the control efficacy of pre-emergence herbicides since flazasulfuron in the tank mix with glyphosate had up to 80% control 15 to 120 days after application (DAA) and grass weed postemergence herbicides, such as propaquizafop + glyphosate and quizalofop + glyphosate, had up to 90% control 15 to 90 DAA. Results confirm the first scientific report of glyphosate-resistant B. rubens worldwide; however, the use of herbicides with another mode of action (MOA) is the best tool for integrated weed management.

The use of pre-emergence herbicides in cassava decreases the need of manual weeding

ABSTRACT Weed management consists of a fundamental practice in cassava, with mechanical and chemical control widely used. The objective of this work was to evaluate the efficacy of pre-emergence herbicides, as well as to determine the interaction of these with weeding complementation in the weed management in cassava. Two experiments were conducted in Junqueiro (Alagoas). In 2015/16, the experimental design was based on randomized blocks, with treatments distributed in a split-split-plot scheme, with four replications. In the main plot, four pre-emergence associations of clomazone + flumioxazin in different doses were evaluated, in addition to a control without herbicide. In the subplots, the Caravela and Pretinha cassava cultivars were evaluated, while in the sub-subplots the control complementation was evaluated using or not the manual weeding. In the 2016/17, the plot design and layout remained the same as for 2015/16, except for the composition of the herbicide treatments, since the standardization of clomazone dose has been chosen, varying only the doses of flumioxazin. The association of clomazone and flumioxazin has shown efficacy in weed control, with a greater residual as higher doses are used. This association provided higher shoot and root yield. Weeding complementation along the cassava cycle can increase its yield.

In-situ paddy straw management practices for higher resource use efficiency and crop productivity in Indo-Gangetic Plains (IGP) of India

The large scale adoption of long duration coarse grain rice varieties and combine harvesting have increased the incidences of in-situ rice residue burning in Indo-Gangetic Plains (IGP). Crop residue burning in addition to causing environmental pollution, is also responsible for loss of precious nutrients (complete nitrogen, about one fourth of phosphorus & potash and about three fourth of sulphur) and efficacy of soil active herbicides. The alternatives to rice residue burning are its removal, incorporation or retention. The in-situ management options are better and further, retention is more advantageous than incorporation in term of energy, time and cost effectiveness. In addition, the surface retention has a series of positive effects, such as, moisture conservation, weed suppression, temperature moderation, and improved soil health. Residue management practices (surface retention or incorporation) also influence the nutrient availability, crop water requirement, weed dynamics, herbicide efficacy, insect-pest infestation and mitigation of climate change effect on long term basis. Hence, the agronomic practices need to be adjusted to prevent temporal nitrogen immobilization, hindrance in precise seeding, weed flora shift, and new insect-pest incidents. Suitable machineries for seeding and harvesting are of paramount importance for proper crop establishment under in-situ residue management practices. Combines fitted with straw management system for uniform spread of straw help in efficient running of conservation agriculture (CA) seeding machines like Turbo Happy Seeder and Rotary Disc Drill. Moreover, for smooth running of CA machinery, the height of anchored straw should be kept as much as possible, so that lesser loose straw is present. The adoption of CA practices (no-tillage and residue retention) in wheat under rice-wheat system can help in improving wheat yield by advanced sowing and reduced problem of Phalaris minor Retz. Moreover, fertilizer application method and timing needs to be fine tuned under in-situ residue management options. The nitrogen top dressing should be done just before irrigation to avoid interception by surface retained residue which can enhance volatilization and immobilization losses of nitrogen. Higher efficacy of pre-emergence herbicides in surface retained residue scenario could also be realized by increasing the spray volume along with modifying the application time and placement of herbicides. Therefore, a paradigm shift in agronomic practices, with respect to paddy straw management, is required for enhancing system productivity and resource use efficiency. DOI: http://doi.org/10.25174/2249-4065/2019/96323

Efficacy of preemergence herbicides over time

AbstractPreemergence herbicides are applied to container-grown nursery crops repeatedly throughout the year, often in 8 to 10 week intervals. Preemergence herbicide efficacy may decline over time, resulting in reduced weed control several weeks after application if weed seed density remains high. The objective of this research is to evaluate efficacy of preemergence herbicides on creeping woodsorrel (Oxalis corniculata L.) and flexuous bittercress (Cardamine flexuosa With.) by applying weed seed from 0 to 10 weeks after herbicide application. Granular formulations of pendimethalin, prodiamine + isoxaben, oxyfluorfen + pendimethalin, and flumioxazin were applied at their maximum labeled rates to separate groups of containers every two weeks for ten weeks. After the herbicide application at 10 weeks, 40 seeds of creeping woodsorrel and flexuous bittercress each were applied to all containers. All herbicides provided effective control when seed were applied within 2 weeks of herbicide application. Herbicides containing oxyfluorfen or flumioxazin provided effective preemergence bittercress and creeping woodsorrel control when seed were applied up to 8 to 10 weeks after herbicide application. Other herbicide products resulted in reduced control as the time between herbicide and seed application increased.Index words: weed control, container crops, substrates.Species used in this study: flexuous bittercress (Cardamine flexuosa With.), creeping woodsorrel (Oxalis corniculata L.).Chemicals used in this study: pendimethalin (Pendulum 2G), prodiamine + isoxaben (Gemini G), pendimethalin + oxyfluorfen (OH2), and flumioxazin (BroadStar).

Effect of Sugar and Alcohol Industry Byproducts on Pre-Emergence Herbicide Efficacy

The present study evaluate the effects of vinasse and filter cake on the efficacy of indaziflam, saflufenacil, and sulfentrazone for the control of morning glory (Ipomoea triloba L.) and crabgrass (Digitaria horizontalis Wiild), as well as the effects of these byproducts on the emergence of these weeds. The experiments were established in a greenhouse with a completely randomized design and four replications at the Agricultural Science Center, Sao Paulo, Brazil, between May 2017 and May 2018. In the first assay, four herbicide doses: indaziflam (0, 37.5, 75, and 150 g ai ha-1), saflufenacil (0, 42, 84, and 168 g a.i ha-1), and sulfentrazone (0, 300, 600, and 1200 g ai ha-1) were applied for pre-emergent weeds in three soil covers (without byproduct, with vinasse, and with filter cake).In the second assay, seven treatments were evaluated, comparing the effects of the different vinasse and filter cake doses, and absence of byproduct on the weeds emergence. When the doses required for 80% effective control were considered, the results showed that for indaziflam, the filter cake negatively affected crabgrass control. In contrast, vinasse had a positive effect on morning glory control by saflufenacil. For sulfentrazone, the filter cake had a negative effect, requiring twice the dose used on the treatment without byproduct for effective morning glory control. Relative to assay 2, the vinasse addition affected the emergence of morning glory but not of crabgrass; however, the filter cake increased the weed biomass accumulation. Vinasse and filter cake byproducts can negatively or positively affect the performance of pre-emergence herbicides, according to the active ingredient used. However, these effects occur at doses below those recommended for the herbicides. Byproducts can affect the emergence and the weed biomass accumulation.

Control of glyphosate-resistant common ragweed in corn with preemergence herbicides

Four field experiments were conducted during 2016 and 2017 to evaluate the efficacy of preemergence herbicides to control glyphosate-resistant common ragweed in corn. Dicamba, dicamba/atrazine, mesotrione + atrazine, isoxaflutole + atrazine, saflufenacil/dimethenamid-P, and S-metolachlor/mesotrione/bicyclopyrone/atrazine were the most efficacious herbicides, providing 94%–100% control of GR common ragweed and reducing density and biomass 98%–100%.

Weed Management in Common Cottonwood (Populus deltoides) Nursery Plantation

AbstractCommon cottonwood-based agroforestry system is widely adopted in Indian Indo-Gangetic plains. The stem cuttings of common cottonwood are raised in a nursery 10 to 12 months in rows spaced 0.5 mx0.5 m, before re-planting in the field. The longer duration of 10 to 12 months and wider spacing of stem cuttings in the nursery makes the entire transplants highly vulnerable to weed competition, especially during early establishment stages. The efficacy of preemergence herbicides and plastic and straw mulches for weed management in common cottonwood nursery was investigated at two sites in years 2014 and 2015. The major weed flora in the experimental field consisted of three grass weeds (crowfootgrass, feather lovegrass, and southern crabgrass), and four broadleaf weeds (scarlet pimpernel, garden spurge, niruri, and lesser swinecress). The integrated use of pendimethalin or alachlor applied PRE with paddy straw mulch significantly reduced density and biomass of both grass and broadleaf weeds compared to herbicide or straw mulch used alone, and provided similar level of weed control to hand weeding at both locations. Spreading of plastic mulch in the whole field after punching holes for common cottonwood stem cuttings, or in row spaces recorded similar weed control to hand-weeding. The integrated use of herbicides with straw mulch, and or plastic mulch alone significantly improved plant height, stem diameter, below- and above-ground biomass of common cottonwood plants compared to unweeded check. The study concluded that integrated use of herbicides plus paddy straw mulch or plastic mulch alone could be adopted for weed management in common cottonwood nursery plantations.

The implications of spatially variable pre-emergence herbicide efficacy for weed management.

BACKGROUNDThe efficacy of pre‐emergence herbicides within fields is spatially variable as a consequence of soil heterogeneity. We quantified the effect of soil organic matter on the efficacy of two pre‐emergence herbicides, flufenacet and pendimethalin, against Alopecurus myosuroides and investigated the implications of variation in organic matter for weed management using a crop–weed competition model.RESULTSSoil organic matter played a critical role in determining the level of control achieved. The high organic matter soil had more surviving weeds with higher biomass than the low organic matter soil. In the absence of competition, surviving plants recovered to produce the same amount of seed as if no herbicide had been applied. The competition model predicted that weeds surviving pre‐emergence herbicides could compensate for sublethal effects even when competing with the crop. The ED50 (median effective dose) was higher for weed seed production than seedling mortality or biomass. This difference was greatest on high organic matter soil.CONCLUSIONThese results show that the application rate of herbicides should be adjusted to account for within‐field variation in soil organic matter. The results from the modelling emphasised the importance of crop competition in limiting the capacity of weeds surviving pre‐emergence herbicides to compensate and replenish the seedbank. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

English

English

Efficacy of Pre-emergence Herbicides for the Control of Major Weeds in Maize (<i>Zea mays</i> L.) at Bako, Western Oromia, Ethiopia

A field experiment was conducted to evaluate efficacy of pre-emergence herbicides against major weeds in maize at Bako during the main rainy season of 2016/17. The trial was laid out in randomized complete block design (RCBD) with three replication, and consisted of five treatments including pre-emergence application of Lunar 537.5 SE at 3L/ha, Venus 500 SC at 6L/ha and Prima gram dual Gold 660sc at 3 L/ha, and two times hand weeding at 25 and 40 DAS and weedy check for comparison. Application treatments boosted maize grain yield over weedy check plots there by reducing weed infestation. Analysis of variance showed statistically significance difference (P < 0.01) for total weed density (m^-2) and dry weight (gm. ^-2). Significantly the minimum density (8.5 m^-2) was observed in plots treated two times hand weeding which was statistically similar with evaluated herbicides. In contrary, the highest (39.1 m^-2) was observed in weedy check plots. All the herbicide treatments provided significant control of weeds causing significant reduction in density of target weed flora and also significantly improved the grain yield in comparison with the weedy check. However, no crop injury was observed in any of the herbicide treatments. The maximum grain yield (57.57 qt ha^-1) was obtained from Lunar 537.5 SE at 3L/ha followed by two times hand weeding (57.08 qt ha^-1) and Venus 500 SC at 6L/ha (54.03 qt ha^-1) having the yield advantage of 67.92, 67.64 and 65.82 respectively, whereas; the minimum (18.47 qt ha^-1) was from weedy check plots. In general application pre-emergence herbicides effectively control weeds in maize and reduce yield losses. Thus, the newly tested pre-emergence herbicides (Lunar 537.5 SE at 3L/ha and Venus 500 SC at 6L/ha) alone could be option to major weeds and increase maize grain yield.

Efficacy of pre-emergence herbicides for control of complex weed flora in transplanted rice

A field experiment was conducted at Chiplima, Sambalpur, Odisha during the rainy season of 2014 and 2015 to study the effect of sand-mix application of pre-emergence herbicides on weed population yield and economics of transplanted rice (Oryza sativa L.). Application of chlorimuron + metsulfuron 4 g/ha, bensulfuron 60 g/ha and pyrazosulfuron 16 g/ha alone was selectively effictive on broad-leaf weeds while pretilachlor 500 g/ha was effective on grasses. Pre-emergence application of pyrazosulfuron with pretilachlor (16 + 500 g/ha) was more effective in minimizing the density (10/m2), biomass (4.8 g/m2) of weeds and enhancing the weed control efficiency (89.3%), grain yield (6.14 t/ha), net returns (` 53.2 x 103/ha) and benefit: cost ratio (1.37) than pretilachlor alone.

Influence of Environmental Factors, Cultural Practices, and Herbicide Application on Seed Germination and Emergence Ecology of Ischaemum rugosum Salisb.

Ischaemum rugosum Salisb. (Saramolla grass) is a noxious weed of rice that is difficult to control by chemical or mechanical means once established. A study was conducted to determine the effect of light, temperature, salt, drought, flooding, rice residue mulch, burial depth, and pre-emergence herbicides on seed germination and emergence of I. rugosum. Germination was stimulated by light and inhibited under complete darkness. Optimum temperature for germination was 30/20°C (97.5% germination). Germination reduced from 31 to 3.5% when the osmotic potential of the growing medium decreased from -0.1 to -0.6 MPa and no germination occurred at -0.8 MPa. Germination was 18 and 0.5% at 50 and 100 mM NaCl concentrations, respectively, but was completely inhibited at 150 mM or higher. Residue application at 1–6 t ha-1 reduced weed emergence by 35–88% and shoot biomass by 55–95%. The efficacy of pre-emergence herbicides increased with increasing application rates and decreased with increasing rice residue mulching. The efficacy of herbicides was in the order of oxadiazon> pendimethalin> pretilachlor. At 6 t ha-1, all herbicides, regardless of rates, did not differ from the control treatment. I. rugosum seeds buried at 2 cm or deeper did not emerge; however, they emerged by 4.5 and 0.5% at 0.5 and 1 cm depths, respectively, compared to the 39% germination for soil surface seeding. Flooding at 4 DAS or earlier reduced seedling emergence and shoot biomass while flooding at 8 DAS reduced only seedling emergence. The depth and timing of flooding independently reduced root biomass. Flooding at 4 and 6 cm depths reduced the root biomass. Relative to flooding on the day of sowing, flooding at 8 DAS increased root biomass by 89%. Similarly, flooding on the day of sowing and at 2 DAS reduced the root–shoot biomass ratio. Under the no-flood treatment, increasing rates of pretilachlor from 0.075 to 0.3 kg ai ha-1 reduced weed emergence by 61–79%. At the flooding depth of 2–4 cm, pretilachlor reduced weed emergence and shoot and root biomass, but the differences across rates were non-significant. Information generated in this study will be helpful in developing integrated weed management strategies for managing this weed.

Época seca e textura do solo afetam o controle químico de Senna obtusifolia em cana-de-açúcar

Devido às suas características intrínsecas, o fedegoso (Senna obtusifolia) tem ganhado importância em canaviais, principalmente onde há predomínio de palhada após a colheita mecânica. O objetivo deste trabalho foi avaliar a eficácia de herbicidas pré-emergentes utilizados na cultura da cana-de-açúcar no controle de fedegoso em solos de diferentes texturas e épocas de aplicação. Foram realizados dois experimentos para cada época de aplicação (seca e úmida), sendo um para cada classe textural de solo (muito-argiloso e franco-argilo-arenoso), totalizando quatro experimentos. Os tratamentos foram constituídos por 17 herbicidas na época úmida e 11 herbicidas na época seca (todos os herbicidas foram aplicados em 50 e 100% da dose recomendada), além da testemunha sem aplicação para cada época e solo, sendo o delineamento inteiramente ao acaso. O tipo de solo e a época de aplicação alteraram a eficiência dos herbicidas. Para a época úmida, inicialmente, todos os herbicidas, exceto trifluralin e s-metolachlor, resultaram em controle satisfatório de fedegoso. Tebuthiuron foi o herbicida que proporcionou maior período residual de controle. Para a época seca, amicarbazone, flumioxazin, hexazinone, imazapic, [diuron + hexazinone] F1 e isoxaflutole foram eficazes em ambos os solos, mas somente em avaliações iniciais; [diuron + hexazinone] F1 e amicarbazone foram os herbicidas que proporcionaram maior período residual de controle.

Preemergence Herbicide Efficacy for Crabgrass (Digitaria spp.) Control in Common Bermudagrass Managed under Different Mowing Heights

Research was conducted at multiple locations throughout the southeastern United States during 2012 and 2013 to assist turf managers in developing integrated programs for managing crabgrass in common bermudagrass turf. Our objective was to determine the effect of mowing height on the efficacy of several pre-emergent (PRE) herbicides labeled for crabgrass control in bermudagrass turf. Plots were established in Raleigh, NC (NCSU), Knoxville, TN (ETREC), and Winder, GA (UGA) and treated with a factorial combination of two mowing heights (1.5 or 3.8 cm), two application regimes [single or split application (initial and an 8-week sequential)], and six preemergent herbicides (dithiopyr, indaziflam, oxadiazon, pendimethalin, prodiamine, and prodiamine + sulfentrazone). In 2012, all herbicides provided greater crabgrass control on plots maintained at 3.8 cm compared with 1.5 cm. This response was not detected in 2013, potentially as a result of above-average rainfall at two of the three trial locations. Analysis revealed mowing height did not affect pendimethalin soil residue, whereas prodiamine concentrations from bermudagrass maintained at 1.5 cm were greater than bermudagrass maintained at 3.8 cm. Therefore, differences in crabgrass control in bermudagrass maintained under different mowing heights may be the result of plant growth, reduced photosynthetically active radiation (PAR) at the soil surface, among other reasons, and not solely differential degradation of applied herbicides at the 1.5- and 3.8-cm mowing heights. Future research should explore effects of increasing bermudagrass mowing height on PAR required for crabgrass germination and growth.