Efficacy Of Glufosinate Research Articles

Identification, mapping, and chemical control of fleabane resistant to glyphosate, chlorimuron, paraquat, and 2,4-D

Abstract Monitoring herbicide-resistant weeds makes it possible to study the evolution and spread of resistance, which provides important information for their management. The objective of this study was to map fleabane accessions in the states of Paraná (PR) and Mato Grosso do Sul (MS), Brazil, to identify herbicide-resistant accessions and their response to soybean preplant chemical burndown management strategies. Fleabane seeds were collected in agricultural areas in PR and MS in 2018, 2019, and 2020. Initial screening was performed for glyphosate, chlorimuron, paraquat, 2,4-D, saflufenacil, and glufosinate efficacy. Subsequently, dose-response experiments were conducted. Field experiments were carried out in three locations, where accessions of multiple herbicide–resistant Sumatran fleabane were identified. Herbicides were used in single or sequential applications at three plant heights (<5 cm, 5 to 10 cm, and >10 cm). After preliminary screening, accessions were classified as putative resistant (<80% control for all four replicates), segregated (<80% control for one to three replicates), or susceptible (>80% control for all four replicates). There was no evidence of resistance to glufosinate or saflufenacil in any of the 461 accessions, while 65 demonstrated possible resistance or segregation to glyphosate only, 235 to glyphosate + chlorimuron, 79 to glyphosate + chlorimuron + paraquat, 59 to glyphosate + chlorimuron + 2,4-D, and 23 with four-way resistance (glyphosate, chlorimuron, paraquat, and 2,4-D). Of these 23 accessions, seven were analyzed using dose-response curves (F2 generation), all from PR, confirming four-way resistance to glyphosate, chlorimuron, paraquat, and 2,4-D. To control resistant Sumatran fleabane, an application should prioritize smaller plants. Despite resistance to 2,4-D, double mixtures containing this herbicide were among the most effective treatments in plants <5 cm in height. If a sequential application is needed for plants >5 cm in height, we recommend glyphosate + synthetic auxin followed by glufosinate or glyphosate + saflufenacil.

Performance of spray nozzles and droplet size on glufosinate deposition and weed biological efficacy

Nozzle type and droplet size are one of the most important factors that affect spray deposition and the efficacy of herbicides. This study focused on evaluating the performance of spray nozzles and droplet sizes on the deposition of glufosinate and its biological efficacy of two weed species. Treatments consisted of spraying glufosinate on Euphorbia heterophylla and Digitaria insularis by five spray nozzles (XR 11002 – fine droplet; TT 11002 – coarse; AIXR 11002 – very coarse; AIXR 110025 – extremely coarse; and TTI 11002 – ultra coarse) assessing the spray deposits and its influence on plant biomass reduction. The spray deposits on E. heterophylla were found to be similar between most of the spray nozzles, except for the TTI 11002 nozzle, which had lower spray deposits. In contrast, for D. insularis, the spray deposits tended to decrease as the droplet size increased. The spray uniformity was lower for the AIXR 11002 nozzle for E. heterophylla and the XR 11002 nozzle for D. insularis. Regarding the efficacy of glufosinate on both weeds, the lower C50 (concentration required for 50% dry weight reduction) were obtained using the XR 11002 nozzle with fine droplets. The TT 11002 nozzle and the AIXR 11002 nozzle showed intermediate C50, making them viable options to reduce spray drift and achieve acceptable weed control. However, the nozzles using extremely coarse (AIXR 110025) and ultra-coarse (TTI 11002) droplet class resulted in higher C50, indicating reduced herbicide efficacy. Our study provided clues on how different spray nozzles and droplet sizes can significantly impact spray deposits and herbicide efficacy on the control of E. heterophylla and D. insularis. Nozzles with fine droplet class generally provided better control, while extremely coarse and ultra-coarse showed reduced efficacy at weed control.

Multistate screening of Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus) sensitivity to glufosinate, dicamba and 2,4-D in the United States

AbstractHerbicide resistance in Palmer amaranth and waterhemp is on the rise and poses a great concern to growers in the United States. A multistate screening was conducted for these two weed species in the United States to assess their sensitivity to glufosinate, dicamba, and 2,4-D. The screening was designed to understand the weed sensitivity landscape and emerging trends in resistance evolution by testing each herbicide at its respective label rate and at half the label rate. A total of 303 weed seed accessions from 21 states representing 162 Palmer amaranth and 141 waterhemp seeds were collected from grower fields in 2019 and screened in greenhouse conditions. Statistical power of different sample sizes and probability of survivors in each accession were estimated for each species and herbicide treatment. Overall, the efficacy of glufosinate, dicamba, and 2,4-D against all these accessions was excellent, with greater than 90% average injury. The variability in herbicide injury, if any, was greater with half the label rate of 2,4-D in some Palmer amaranth accessions, while waterhemp accessions had exhibited variable sensitivity with half the label rate of dicamba and glufosinate. The study highlights the value of monitoring weeds for herbicide sensitivity across broader landscape and the importance of glufosinate, dicamba, and 2,4-D herbicides in managing troublesome weeds as part of a diversified weed control program integrated with other chemical, mechanical and cultural practices.

Early detection of the herbicidal effect of glyphosate and glufosinate by using hyperspectral imaging

AbstractEarly detection of non‐optimal weed control is now a priority to ensure herbicide efficacy. This study aimed to evaluate the potential of hyperspectral imaging (HSI) for early detection of the effects of glyphosate and glufosinate on weeds. Specific features (bands and vegetation indices [VIs]) were extracted as indicators for glyphosate and glufosinate efficacy. Black nightshade (Solanum nigrum L.) was used as the model weed and treated with glyphosate or glufosinate at the fourth‐leaf stage. Plants were imaged in the laboratory at 6, 24, 48, 72, and 96 hours after treatment (HAT) with a 204‐wavelength (400–1000 nm) hyperspectral camera. The impact of the herbicide treatments on the spectral reflectance values was analyzed using the two‐sided Mann–Whitney U test, followed by classification with a machine learning (ML) model applied on the full spectrum and on 12 VIs. In addition, the contribution of the different wavelengths (features) to classification accuracy was assessed using a feature selection process. For glufosinate, 95% classification accuracy was observed as early as 6 HAT, with four features from the green region required. For glyphosate, four features from the red, red‐edge, and green regions were used to achieve 88% classification accuracy at 24 HAT. The accuracy of VIs‐based classification was generally lower than that of the full spectrum classification accuracy. Above 85% classification accuracy was achieved only at later imaging campaigns, starting at 48 HAT. This study thus demonstrates that non‐optimal application of glyphosate and glufosinate can indeed be detected using spectral imaging.

Influence of Glufosinate Rate, Ammonium Sulfate, and Weed Height on Annual Broadleaf Weed Control

Weed control efficacy with contact herbicides can depend on weed height at application. Four field experiments were conducted at sites with multiple weed species at different heights to determine the effect of weed height, glufosinate rate, and the addition of ammonium sulfate (AMS) on annual broadleaf weed control in soybean in southwestern Ontario, Canada, during 2021 and 2022. Glufosinate was applied at 300 or 500 g ai ha-1 without or with 6.50 L ha-1 of AMS to 5, 10, and 15 cm tall common lambsquarters (Chenopodium album L.), common ragweed (Ambrosia artemisiifolia L.), velvetleaf (Abutilon theophrasti Medik.), and redroot pigweed (Amaranthus retroflexus L.). Glufosinate provided excellent common ragweed control (> 98%) at both rates, without and with AMS, and at all three heights 4 weeks application (WAA). In contrast, glufosinate efficacy declined when applied to common lambsquarters, velvetleaf, and redroot pigweed > 5 cm in height. The addition of AMS to glufosinate improved common lambsquarters control. Increasing the rate of glufosinate to 500 g ai ha-1 and the addition of AMS improved control of velvetleaf and redroot pigweed. The results of this study demonstrate that the effect of glufosinate rate, AMS addition, and weed height at application timing is weed species-specific. In general, glufosinate (300 g ai ha-1) controlled common annual broadleaf weeds if weeds were < 5 cm in height; otherwise, glufosinate needed to be applied at 500 g ai ha-1 with AMS for control of annual broadleaf weeds, especially common lambsquarters, velvetleaf and redroot pigweed. 

Glyphosate resistance in junglerice (Echinochloa colona) and alternative herbicide options for its effective control

AbstractControl of glyphosate-resistant (GR) junglerice is a challenging task in eastern Australia. There is limited information on the efficacy and reliability of alternate herbicides for GR populations of junglerice, especially when targeting large plants and when temperatures are high. A series of experiments were conducted to confirm the level of glyphosate resistance in three populations of junglerice and to evaluate the efficacy of alternate herbicides for the control of GR junglerice populations. The LD50 of glyphosate of B17/7, B17/34, and B17/35 populations was found to be 298, 2,260, and 1,715 g ae ha–1, respectively, suggesting that populations B17/34 and B17/35 were highly resistant to glyphosate. Glyphosate efficacy was reduced at high-temperature (35 C day/25 C night) compared with low-temperature conditions (25 C day/15 C night), suggesting that control of susceptible populations may also be reduced if glyphosate is sprayed under hot conditions. Preemergence herbicides dimethenamid-P (1,000 g ai ha–1) and pendimethalin (1,500 g ai ha–1) provided 100% control of GR populations (B17/34 and 17/35). Postemergence herbicides, such as clethodim (60 or 90 g ai ha–1), glufosinate (750 g ai ha–1), haloxyfop (52 or 78 g ai ha–1), and paraquat (400 or 600 g ai ha–1), applied at the four-leaf stage provided 100% control of GR populations. For larger junglerice plants (eight-leaf stage), postemergence applications of paraquat (400 or 600 g ai ha–1) provided greater weed control than clethodim, glufosinate, and haloxyfop. A mixture of either glufosinate or haloxyfop with glyphosate provided poor control of GR junglerice populations compared with application of glufosinate or haloxyfop applied alone. Efficacy of glufosinate and haloxyfop for the control of GR populations decreased when applied in the sequential spray after glyphosate application. This study identified alternative herbicide options for GR junglerice populations that can be used in herbicide rotation programs for sustainable weed management.

Influence of surfactant‐humectant adjuvants on physical properties, droplet size, and efficacy of glufosinate formulations

AbstractGlufosinate efficacy is inconsistent among weed species and under environmental conditions that favor rapid droplet drying. Surfactant‐humectant adjuvants could maximize glufosinate efficacy by increasing wetting and penetration into the leaf surface while decreasing evaporation rate (ER). However, there is a lack of information in the literature about the interaction of surfactant‐humectants adjuvants with glufosinate. The objective of this study was to investigate the influence of surfactant‐humectant adjuvants on the physical properties, droplet size, and efficacy of two glufosinate formulations. Laboratory, greenhouse, and field studies were conducted at the Pesticide Application Technology Laboratory of the University of Nebraska‐Lincoln. Treatment design was a 2 × 5 factorial with two glufosinate formulations combined with five adjuvant treatments plus an untreated control. Density and viscosity of glufosinate solutions mostly increased with the addition of adjuvants. However, the influence of the adjuvants on dynamic surface tension (dST), static contact angle (sCA), and evaporation rate (ER) varied by glufosinate formulation, adjuvant, and relative humidity (RH). Under greenhouse conditions, an improvement in efficacy by adding adjuvants was mainly observed for Interline solutions. The addition of adjuvants to Interline solutions increased biomass reduction up to 19 and 35% for common lambsquarters (Chenopodium album L.) and kochia [Bassia scoparia (L.) A. J. Scott], respectively. Also, some of the adjuvants presented null or antagonistic influence on herbicide efficacy. No increase in control, biomass reduction, and mortality of horseweed (Erigeron canadensis L.) and Palmer amaranth (Amaranthus palmeri S. Watson) was observed with the use of adjuvants under field conditions. Herbicide‐adjuvant‐plant‐environment interaction is complex. Thus, the use of surfactant‐humectant adjuvants may not increase herbicide efficacy.

Biochemical Basis for the Time-of-Day Effect on Glufosinate Efficacy against Amaranthus palmeri

Glufosinate, a glutamine synthetase (GS) inhibitor, often provides variable weed control depending on environmental conditions such as light, temperature and humidity at the time of application. Midday applications normally provide improved efficacy compared to applications at dawn or dusk. We investigated the biochemical basis for the time-of-day effect on glufosinate efficacy in Amaranthus palmeri. GS1/GS2 gene expression and GS1/GS2 protein abundance were assessed in different parts (young leaves, old leaves, and roots) of plants incubated in the dark compared to those in the light. The turnover of GS total activity was also evaluated overtime following glufosinate treatment at midday compared to dusk application. The results suggest that GS in A. palmeri is less expressed and less abundant in the dark compared to in the light. Midday application of glufosinate under intense light conditions following application provide full control of A. palmeri plants. Consequently, these plants are unable to recover GS activity by de novo protein synthesis. Full activity of GS is required for complete inhibition by the irreversible inhibitor glufosinate. Therefore, glufosinate applications should always be performed in the middle of the day when sunlight is intense, to prevent weed escapes from the herbicide treatment.

Palmer Amaranth Control by Glufosinate Depends on Application Time of Day

Glufosinate is used widely to control glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) in cotton (Gossypium hirsutum L.). Previous research has shown weed control with several herbicides, including glufosinate, can be affected by application time of day. The response sometimes has been attributed to diurnal leaf movement (leaf orientation) in the weeds. The objectives of our research were to determine the influence of time of day of glufosinate application on Palmer amaranth control and to determine if the response was related to diurnal leaf orientation. Field experiments in five states evaluated Palmer amaranth control with glufosinate applied at nine intervals ranging from 1 h before sunrise to 6 h after sunrise and nine intervals ranging from 6 h before sunset to 1 h after sunset. Greatest Palmer amaranth control was achieved with glufosinate applied 2 h after sunrise to 1 h before sunset. Ammonium sulfate, added only to glufosinate 1 h before sunrise or 1 h after sunset treatments, did not improve control. Leaf angles of Palmer amaranth and velvetleaf (Abutilon theophrasti L.) were determined in a greenhouse at 1 h before light, 2 h after light, mid-day, 2 h before dark, and 1 h after dark. Leaves of velvetleaf oriented downward during the dark periods but time of day had no effect on leaf orientation of Palmer amaranth. These results demonstrate the need for sunlight for optimum glufosinate efficacy on Palmer amaranth.

Palmer amaranth control, fecundity, and seed viability from soybean herbicides applied at first female inflorescence

AbstractPalmer amaranth is an extremely troublesome weed for soybean growers because of its aggressive growth, adaptability, prolific seed production, and widespread resistance to many herbicides. Studies were initiated to determine the effects of herbicide application at first female inflorescence on Palmer amaranth control, biomass, seed production, cumulative germination, and seed viability. Enlist (2,4-D–resistant) soybean and Xtend (dicamba-resistant) soybean were planted and various combinations of either 2,4-D or dicamba with and without glufosinate and/or glyphosate were applied at first visible female Palmer amaranth inflorescence. Mixtures of 2,4-D + glufosinate and 2,4-D + glufosinate + glyphosate provided the greatest control at 4 wk after treatment in Enlist soybean. Similarly, in Xtend soybean, combinations of dicamba + glufosinate and dicamba + glufosinate + glyphosate provided the greatest control. The greatest reductions in biomass were from combinations of auxin herbicides (2,4-D or dicamba) plus glufosinate with and without glyphosate. Seed production was reduced most by treatments containing at least one effective site of action: an auxin herbicide (2,4-D or dicamba) or glufosinate. In contrast to previous research, cumulative germination and seed viability were not affected by herbicide treatments. This research indicates the efficacy of auxin herbicides or glufosinate alone and in combination to reduce the seed production of Palmer amaranth when applied at first female inflorescence. More research is needed to evaluate the full potential for applications of these herbicides at flower initiation to mitigate the evolution of herbicide resistance.

Carrier Volume and Nozzle Effect on 2,4-D and Glufosinate Performances in Hazelnut Sucker Control

Hazelnut (Corylus avellana L.) basal sprouts, or suckers, are removed to train trees as a single trunk, facilitating mechanization. Suckers are routinely controlled with herbicides, often by using nozzles that generate fine droplets and spray volumes as high as 934 L·ha−1, making spray drift a concern. Spray nozzle type and carrier volume can impact herbicide efficacy and drift. Field studies compared the efficacy of 2,4-D and glufosinate in controlling suckers when applied with a flat-fan nozzle, producing fine droplets, to a TeeJet air-induction nozzle, producing ultra-coarse droplets. These nozzles were evaluated at 187 and 374 L·ha−1. Nozzle and carrier volume did not affect the efficacy of 2,4-D based on control, sucker height, or dry weight. The efficacy of glufosinate was unaffected by nozzle type or spray volume in most evaluations. These results indicate that hazelnut suckers can be effectively controlled using drift-reduction nozzles with lower carrier volumes (187 L·ha−1). Drift-reduction nozzles, coupled with lower spray volume, can maintain herbicide efficacy, minimize drift risk, and reduce cost.

Timing and Application Rate for Sequential Applications of Glufosinate are Critical for Maximizing Control of Annual Weeds in LibertyLink® Soybean

Preserving the utility of glufosinate in both LibertyLink soybean and other glufosinate-resistant crops is critical for managing herbicide-resistant weeds. An experiment with a two-factor factorial arrangement was conducted at the Arkansas Agricultural Research and Extension Center in Fayetteville, AR, in 2015, 2016, and 2017 to evaluate the efficacy of glufosinate in single and sequential applications at various rates on 8–32 cm tall Palmer amaranth, barnyardgrass, and broadleaf signalgrass. Herbicide treatments consisted of glufosinate applied at 454, 595, 738, and 882 g ai ha−1 (Factor 1) with either no sequential application or a sequential application occurring 7, 10, 14, or 21 days after the initial application (DAI) (Factor 2). For treatments that contained a sequential application, the same rate used in the initial application (e.g., 451 g ai ha−1) was also used in the sequential. Regardless of species and rate, sequential applications were always superior to single applications. Palmer amaranth control 3 weeks after the final treatment (WAF) was 8% greater when the sequential application occurred 10 DAI compared to 21 DAI, averaged over glufosinate rates. When at least 595 g ai ha−1 glufosinate was used in a treatment, no differences between the 7-, 10-, 14-, and 21-day sequential application intervals were observed for barnyardgrass or broadleaf signalgrass control, 3 WAF. Soybean yields were greater when the glufosinate applications occurred 7 or 10 d apart compared to 21 d, averaged over glufosinate rates. When large weeds are present in the field, these data suggest that glufosinate should be applied sequentially with a 7- to 14-day interval between applications. If sequential applications of glufosinate are used in combination with a comprehensive weed control management program, the value of the LibertyLink technology should be preserved by mitigating the risk of glufosinate resistance.

Glufosinate enhances the activity of protoporphyrinogen oxidase inhibitors

AbstractGlufosinate inhibits glutamine synthetase (GS), a key enzyme for amino acid metabolism and photorespiration. Protoporphyrinogen oxidase (PPO) inhibitors block chlorophyll biosynthesis and cause protoporphyrin accumulation, a highly photodynamic intermediate. Both herbicides ultimately lead to plant death by a massive accumulation of reactive oxygen species (ROS) through different mechanisms. We investigated a potential synergistic effect by the mixture of the two herbicide mechanisms of action (MoAs). The tank mix between a low rate of glufosinate (280 g ai ha−1) with an ultra-low dose of saflufenacil (1 g ha−1) provided enhanced herbicidal activity compared with the products applied individually on Palmer amaranth (Amaranthus palmeriS. Watson). The synergism between the two herbicides was also confirmed by isobole analysis and field trials. The herbicide combination provided high levels of efficacy when applied at low temperature and low humidity. Mechanistically, glufosinate caused a transient accumulation of glutamate, the building block for chlorophyll biosynthesis. Consequently, inhibition of both GS and PPO resulted in greater accumulation of protoporphyrin and ROS, forming the physiological basis for the synergism between glufosinate and PPO inhibitors. While the synergy between the two herbicide MoAs provided excellent efficacy on weeds, it caused low injury to PPO-resistant waterhemp [Amaranthus tuberculatus(Moq.) Sauer] and high injury to both glufosinate-resistant and glufosinate-susceptible soybean [Glycine max(L.) Merr.]. Glufosinate enhances the activity of PPO inhibitors through glutamate and protoporphyrin accumulation, leading to increased levels of ROS and lipid peroxidation. The synergism between the two herbicide MoAs can help to overcome environmental effects limiting the efficacy of glufosinate. Future research is needed to optimize the uses for this herbicidal composition across different cropping systems.

Utility of glufosinate in postemergence row middle weed control in Florida plasticulture production

AbstractHerbicides are the foundation for row-middle weed control in Florida plasticulture production. Paraquat is commonly used as a burndown herbicide, and resistance issues have subsequently developed. Halosulfuron is mixed with PRE and POST herbicides to provide additional control of nutsedge. The objective of the study was to determine glufosinate efficacy on weeds emerging in the row-middle and suitability in mixture with halosulfuron for nutsedge control. For total weed control, the high dose of glufosinate (983 g ai ha–1) gave the highest overall control (98% and 64% at 4 wk after treatment for experiments 1 and 2, respectively), and the low rate of glufosinate (656 g ha–1) (67% and 39%) gave results comparable to paraquat (57% and 44%). The high glufosinate dose and paraquat gave comparable control of Brazil pusley (74% to 77% control). Glufosinate + halosulfuron mixture had lower efficacy on Brazil pusley than halosulfuron + paraquat mixture. Glufosinate application reduced grass densities, whereas paraquat did not. Increasing the glufosinate dose did not further decrease grass densities. Similar trends in grass control were also demonstrated in their respective mixtures. Mixing halosulfuron with glufosinate or paraquat did not provide consistent reductions in nutsedge densities, nor did adding paraquat or glufosinate further reduce densities compared with halosulfuron alone for the 4-wk study period. Both paraquat and glufosinate antagonized halosulfuron and reduced efficacy on nutsedge. Compared to controls, there was a reduction between expected and actual nutsedge control for paraquat and glufosinate (25% and 36%), respectively. For total weed control, glufosinate is a suitable alternative to paraquat for row-middle weed management in vegetable production.

Spray droplet size and carrier volume effect on dicamba and glufosinate efficacy.

Pesticide applications using a specific droplet size and carrier volume could maximize herbicide efficacy while mitigating particle drift in a precise and efficient manner. The objectives of this study were to investigate the influence of spray droplet size and carrier volume on dicamba and glufosinate efficacy, and to determine the plausibility of droplet-size based site-specific weed management strategies. Generally, across herbicides and carrier volumes, as droplet size increased, weed control decreased. Increased carrier volume (187 L ha-1 ) buffered this droplet size effect, thus greater droplet sizes could be used to mitigate drift potential while maintaining sufficient levels of weed control. To mitigate drift potential and achieve satisfactory weed control (≥ 90% of maximum observed control), a 900 µm (Ultra Coarse) droplet size paired with 187 L ha-1 carrier volume is recommended for dicamba applications and a 605 µm (Extremely Coarse) droplet size across carrier volumes is recommended for glufosinate applications. Although general droplet size recommendations were created, optimum droplet sizes for weed control varied significantly across site-years. Convoluted interactions occur between droplet size, carrier volume, and other application parameters. Recommendations for optimizing herbicide applications based on droplet size should be based on a site-specific management approach to better account for these interactions. © 2018 Society of Chemical Industry.

First Case of Glufosinate-Resistant Rigid Ryegrass (Lolium rigidum Gaud.) in Greece

Repeated applications of the same herbicide(s), which are characterized by the same mode of action, increase selection pressure, which in turn favours the evolution of herbicide-resistant weeds. Glufosinate is a broad-spectrum non-selective herbicide being used for weed control for many years around the world. Rigid ryegrass (Lolium rigidum Gaud.) is an economically important grass weed in Greece. Recent complaints by growers about control failure of rigid ryegrass with glufosinate require further investigation and have been the basis of this study. The objectives of this study were to confirm the existence of glufosinate-resistant L. rigidum in Greece and evaluate the effect of L. rigidum growth stage on glufosinate efficacy. Twenty populations of rigid ryegrass from Greece were sampled from five regions, and whole plant dose–response studies were conducted for five populations under controlled conditions with eight rates of glufosinate (0.0, 0.098, 0.187, 0.375, 0.75, 1.5, 3.0, and 6.0 kg a.i. ha−1). Glufosinate resistance was confirmed in three out of five populations with the level of resistance ranging from three-to seven-fold compared with the susceptible populations based on above-ground biomass reduction. Results also revealed that the level of glufosinate-resistance of rigid ryegrass was dependent on the growth stage at which it was applied.

Potential Role of Sequential Glufosinate and Foramsulfuron Applications for Management of Fescues (Festucaspp.) in Wild Blueberry

Sheep and hair fescue are perennial, tuft forming grasses that spread by seed and form dense sods in wild blueberry fields. These sods compete with the crop for resources and hinder harvest. Field and greenhouse studies were conducted in 2015 to evaluate 1) the effect of sequential glufosinate and foramsulfuron applications on suppression of fescues in the greenhouse and field, and 2) efficacy of glufosinate and foramsulfuron on fescue seedlings when applied at 2, 4, 6, and 8 wk after seedling emergence in the greenhouse. Glufosinate applications at 750 and 1,005 g ai ha−1followed by foramsulfuron application at 35 g ai ha−1reduced fescue leaf number and biomass relative to foramsulfuron application alone in the greenhouse. In the field study, fescue flowering tuft density, tuft inflorescence height, seed production, and seed viability were reduced by foramsulfuron alone, but there was a trend towards lower seed production and tuft height when fescues were treated with glufosinate at 1,005 g ha−1followed by foramsulfuron. Foramsulfuron caused low seedling mortality at all application timings evaluated, but glufosinate caused >90% mortality in seedlings when applied at 2, 4, 6, or 8 wk after seedling emergence. Our results suggest that sequential applications of these herbicides are less effective under field conditions relative to results obtained in the greenhouse, though burndown glufosinate applications may have a role in reducing fescue seedling recruitment. Additional research should be conducted to determine the effect of early spring and autumn glufosinate applications on fescue seedling recruitment and suppression of established fescue tufts with subsequent foramsulfuron applications.

Glufosinate Efficacy as Influenced by Carrier Water pH, Hardness, Foliar Fertilizer, and Ammonium Sulfate

Carrier water quality is an important consideration for herbicide efficacy. Effect of carrier water pH (4, 6.5, or 9) and coapplied Zn or Mn foliar fertilizer was evaluated on glufosinate efficacy for horseweed and Palmer amaranth control in the field. Greenhouse studies were conducted to evaluate the effect of: (1) carrier water pH, foliar fertilizer (Zn, Mn, or without fertilizer), and ammonium sulfate (AMS) (at 0 or 2.5% v/v); and (2) carrier water hardness (0 to 1,000 mg L−1) and AMS (at 0 or 2.5% v/v) on glufosinate efficacy for giant ragweed, horseweed, and Palmer amaranth control. In a 2014 field study, control, plant density reduction, and biomass reduction were at least 8% greater for horseweed and at least 14% greater for Palmer amaranth when glufosinate was applied at carrier water pH 4 compared with pH 9. Glufosinate efficacy was at least 10 and 17% greater for giant ragweed and Palmer amaranth control, respectively, with carrier water pH 4 compared with pH 9 in the greenhouse. In the greenhouse studies, coapplied Zn or Mn fertilizer had no effect on glufosinate efficacy. Increased carrier water hardness from 0 to 1,000 mg L−1negatively influenced glufosinate efficacy and resulted in 20 and 17% lesser control and biomass reduction, respectively, on giant ragweed or Palmer amaranth. Use of AMS enhanced glufosinate efficacy on giant ragweed control in both greenhouse studies, whereas only the Palmer amaranth control was enhanced in the water hardness study. Horseweed control with glufosinate as affected by carrier water pH, hardness, or AMS remained unaffected in both greenhouse studies. Carrier water at alkaline pH or hardness > 200 mg L−1has potential to reduce glufosinate efficacy. Therefore, carrier water free of hardness cations and at acidic condition (pH = 4 to 6.5) should be considered for optimum glufosinate efficacy.

Effect of five desiccants applied alone and in combination with glyphosate in dry edible bean (Phaseolus vulgaris L.)

McNaughton, K. E., Blackshaw, R. E., Waddell, K. A., Gulden, R. H., Sikkema, P. H. and Gillard, C. L. 2015. Effect of five desiccants applied alone and in combination with glyphosate in dry edible bean (Phaseolus vulgaris L.). Can. J. Plant Sci. 95: 1235–1242. Application of dry bean desiccants just prior to crop maturity is common practice by Canadian producers. As dry beans are grown for human consumption it is critical that producers pick desiccants that do not affect crop yield, seed quality, or result in desiccant seed residue levels above accepted levels. In this study the efficacy of glyphosate, diquat, glufosinate, carfentrazone, flumioxazin, and saflufenacil as desiccants was examined for navy, cranberry, pinto, and great northern dry bean. Seed herbicide residues were also tested for each of the dry bean classes tested. Navy, cranberry, pinto, and great northern dry bean yields were not impacted by use of the desiccants diquat, carfentrazone, flumioxazin, or saflufenacil when applied at labelled rates and application timings. Additionally, herbicide residues in seed following application remained lower than maximum residue limits (MRL) established by primary Canadian dry bean export partners. Generally, dry bean colour, irrespective of class, was not altered by desiccant use; diquat and flumioxazin caused minor increases in the degree of red and yellow seed pigmentation for cranberry bean only. Although colour differences were noted using a Chroma meter the differences were slight and would not likely be of economic importance. Application of glyphosate did not affect crop yield, and seed residue levels were below MRLs for navy, pinto, and great northern bean. However, seed glyphosate residue levels were above the MRL for cranberry bean when glyphosate was applied alone or tankmixed with carfentrazone, flumioxazin, or saflufenacil. Seed residue levels were also above listed MRLs for some export countries when glufosinate was applied to navy, cranberry, and pinto bean, although crop yield and seed quality remained unaffected. These findings suggest that growers and contractors should avoid using glufosinate as a dry bean desiccant at least for some markets and that care should be taken when selecting glyphosate as a desiccant, especially for cranberry bean. Across all market classes desiccation progress of bean leaf, stem, and pod tissue was slowest when glyphosate and carfentrazone were used.

Performance of Postemergence Herbicides Applied at Different Carrier Volume Rates

POST weed control in soybean in the United States is difficult because weed resistance to herbicides has become more prominent. Herbicide applicators have grown accustomed to low carrier volume rates that are typical with glyphosate applications. These low carrier volumes are efficient for glyphosate applications and allow applicators to treat a large number of hectares in a timely manner. Alternative modes of action can require greater carrier volumes to effectively control weeds. Glyphosate, glufosinate, lactofen, fluazifop-P, and 2,4-D were evaluated in field and greenhouse studies using 47, 70, 94, 140, 187, and 281 L ha−1carrier volumes. Spray droplet size spectra for each herbicide and carrier volume combination were also measured and used to determine their impact on herbicide efficacy. Glyphosate efficacy was maximized using 70 to 94 L ha−1carrier volumes using droplets classified as medium. Glufosinate efficacy was maximized at 140 L ha−1and decreased as droplet diameter decreased. For 2,4-D applications, efficacy increased when using carrier volumes equal to or greater than 94 L ha−1. Lactofen was most responsive to changes in carrier volume and performed best when applied in carrier volumes of at least 187 L ha−1. Carrier volume had little impact on fluazifop-P efficacy in this study and efficacy decreased when used on taller plants. Based on these data, applicators should use greater carrier volumes when using contact herbicides in order to maximize herbicide efficacy.