Ai Ha Research Articles

Metabolism of Tembotrione, a Triketone Herbicide, confers Differential Sensitivity in Winter Wheat (Triticum aestivum).

Tembotrione is a triketone herbicide widely used for broad-spectrum weed control in corn but not registered for use in wheat. A wide collection of spring, winter, and EMS-derived mutant lines of wheat was evaluated for their response to tembotrione treatment. Two winter wheat (WW) genotypes (WW-1 and WW-2) were found to be least sensitive to this herbicide, surviving >6 times the field recommended dose (92 g ai ha-1) compared to the most sensitive genotype (WW-24). Further, HPLC analysis using [14C] tembotrione suggested that both WW-1 and WW-2 metabolized tembotrione rapidly to nontoxic metabolites. Pretreatment with a P450 inhibitor (malathion) followed by tembotrione application increased the sensitivity of WW-1 and WW-2 genotypes to this herbicide, suggesting likely involvement of P450 enzymes in metabolizing tembotrione similar to corn. Overall, our results suggest that the genotypes WW-1 and WW-2 can potentially be used to develop tembotrione-resistant wheat varieties.

Chemical Control Against Aggressive Broad Leaves Weed Ipomea sp. in Drill Seeded-rice (Oryza sativa L.)

Two field experiments were carried out at the Experimental Farm of Rice Department, Sakha Agricultural Research Station, Kafrelsheikh, Egypt throughout 2020 and 2021 summer seasons to identify an efficient chemical control program against Ipomea sp. as perennial Convolvulaceae weed in drill seeded-rice. The experimental design was split-plot with three replications. Three times of herbicidal application at 20, 30 and 40 days after sowing (DAS) were allocated randomly in main plots, while in sub-plots, six weed control treatments were randomly distributed included three single herbicides application (bentazone at rate of 1.714 kg ai ha-1, fluroxypyr at rate of 0.0952 kg ai ha-1 and bensulfuron-methyl at rate of 0.0714 kg ai ha-1) in addition to two herbicide mixtures were bentazone + fluroxypyr (1.344 kg ai ha-1 + 0.0952 kg ai ha-1) and bensulfuron + fluroxypyr (0.0714 kg ai ha-1 + 0.0952 kg ai ha-1) as compared to un-treated (weedy check) plots. Chemical control at early stage (20 DAS) achieved the best Ipomea control and recorded the lowest values of tillers number m-2, fresh and dry weights during 2020 and 2021, consequently recorded the highest rice dry matter, panicles number m-2, panicle weight and grain yield during both seasons. The results also showed that herbicide mixtures exceeded single application of herbicide in controlling Ipomea as broad leaf weed, bentazon + fluroxypyr ranked first in weed control efficiency percentage and recorded the lowest weed density m-2, fresh and dry weights of Ipomea during the two seasons of study as well as achieved the best values in rice dry matter, panicles per square meter, panicle weight and grain yield during 2020 and 2021 seasons, while the mixture of bensulfuron + fluroxypyr ranked second in this respect. The combination of bentazone + fluroxypyr sprayed at 20 DAS recorded the best Ipomea chemical control efficiency (95.4 %) and recorded the best rice grain yield (9.322 t ha-1) as an average for Giza 178 cv under drill seeded-rice conditions.

Response of conventional sunflower cultivars to drift rates of synthetic auxin herbicides.

The agrochemical industry has launched several new synthetic auxin herbicides in rice to combat increasing numbers of herbicide resistant weeds to other modes of action. Excessive or inappropriate use of these herbicides has resulted in unintended consequences near the sites of application, such as herbicide drift. This study was conducted to determine the impact of drift of quinclorac and florpyrauxifen-benzyl+penoxsulam (FBP) on the yield and yield components of two sunflower cultivars. In a growth chamber experiment, quinclorac and FBP were applied to 2-4 true leaf stages at rates ranging from 2.93 to 93.75 and from 0.51 to 16.25 g ai ha-1, respectively. Nonlinear regression analyses indicated that the cultivar Bosfora was more sensitive to quinclorac and FBP than the cultivar Tunca. In field experiments, these sunflower cultivars were treated with drift rates of quinclorac (<375 g ai ha-1) and FBP (<65 g ai ha-1) when they were at the 8-10 true leaf stage. Quinclorac and FBP drift rates resulted in up to 52-61% and 85-100% injury and 82-88% and 100% yield loss, respectively. Crop injury and yield data clearly showed that cultivar Bosfora was more sensitive to FBP and quinclorac rates than cultivar Tunca, and both cultivars were more sensitive to FBP than quinclorac. In our work, we also found that plant height reduction caused by quinclorac at early growth stages may be a valuable indicator to evaluate crop injury and yield loss.

Confirming resistance to PPO-inhibiting herbicides applied preemergence and postemergence in a Georgia Palmer amaranth population

Abstract Herbicides that inhibit protoporphyrinogen oxidase (PPO) are used in more than 40 agronomic and specialty crops across Georgia to manage weeds through residual and postemergence (POST) control. In 2017, a population of Palmer amaranth exhibiting reduced sensitivity to POST applications of PPO-inhibiting herbicides was identified by the University of Georgia. Seed were collected from the site along with a known sensitive population; distance between the samples was 200 m, increasing the likelihood of similar environmental and genetic characteristics. To quantify sensitivity for both preemergence (PRE) and POST uses, 21 greenhouse dose-response assessments were conducted from 2017 to 2022. After conducting initial rate-response studies, 13 doses per herbicide were chosen for the POST experiment; field use rates of fomesafen (420 g ai ha−1), lactofen (219 g ai ha−1), acifluorfen (420 g ai ha−1), and trifludimoxazin (25 g ai ha−1) ranging from 0× to 4× the field use rate for the susceptible population, and 0× to 40× for the suspect population were applied. Herbicide treatments included adjuvants and were applied to plants 8 to 10 cm in height. Relative resistance factors (RRFs) were calculated for control ratings, mortality, and biomass, and ranged from 105 to 318, 36 to 1,477, 215 to 316, and 9 to 49 for fomesafen, lactofen, acifluorfen, and trifludimoxazin, respectively. In the PRE experiment, herbicide applications included five to nine doses of fomesafen (1× = 210 g ai ha−1), flumioxazin (1× = 57 g ai ha−1), oxyfluorfen (1× = 561 g ai ha−1), and trifludimoxazin (1× = 38 g ai ha−1); doses ranged from 0× to 6× for the suspect population and 0× to 2× for the susceptible population. Visual control, mortality, and biomass RRFs ranged from 3 to 5 for fomesafen, 21 to 31 for flumioxazin, 6 to 22 for oxyfluorfen, and 8 to 38 for trifludimoxazin. Results confirm that a Georgia Palmer amaranth population is resistant to PPO-inhibiting herbicides applied both PRE and POST.

Evaluation of herbicide programs for the control of knotroot foxtail [Setaria parviflora (Poir.) Kerguélen] in bermudagrass pasture

Abstract Knotroot foxtail has become more prevalent and problematic in pastures and hayfields in the southeastern United States. Gaps exist in our knowledge of which herbicide practices are best for managing this species in bermudagrass forage production. This study was conducted to determine the efficacy of various ways to control knotroot foxtail in bermudagrass with herbicide applications in autumn, postemergence (POST), with and without also applying a herbicide in preemergence (PRE), in spring. The study was a randomized complete block with a factorial arrangement of treatments and included a nontreated control for both fall and spring timings. Glyphosate at two rates (0.35 or 0.7 kg ae ha−1), nicosulfuron (0.07 kg ai ha−1) + metsulfuron (0.012 kg ai ha−1), and hexazinone (1.3 kg ai ha−1) were applied alone in the fall or followed by indaziflam (0.067 kg ai ha−1) or pendimethalin (4.46 kg ai ha−1) in the spring. Three harvests were conducted throughout the growing season to evaluate weed species (knotroot foxtail, large crabgrass, and horsenettle) and bermudagrass biomass as well as overall species composition. The combination of fall and spring treatments did not affect weed species or bermudagrass biomass. Therefore, treatment main effects were analyzed by fall or spring application timing. A spring application of either pendimethalin or indaziflam increased bermudagrass biomass compared with that of the nontreated control. However, neither PRE herbicide effectively reduced knotroot foxtail biomass compared with the nontreated control, although pendimethalin did reduce season-long knotroot foxtail composition. Spring PRE herbicides are an effective tool for forage producers, but further research is needed to identify effective herbicides and additional approaches for the control of knotroot foxtail.

Control of Echinochloa spp. and Leptochloa fascicularis with the novel dihydroorotate dehydrogenase inhibitor herbicide tetflupyrolimet in California water-seeded rice

Abstract The spread of herbicide-resistant weeds is considered a major problem for rice production in California, and there is a need for new herbicides. Tetflupyrolimet is a new herbicide with a novel dihydroorotate dehydrogenase–inhibiting site of action that has strong activity on grasses. Three field studies were conducted at the California Rice Experiment Station in Biggs, CA, in 2022 and 2023 to (1) determine control of watergrass species and bearded sprangletop with tetflupyrolimet, (2) characterize the effects of tetflupyrolimet combined with other herbicides on weed control and rice, and (3) determine the response of rice cultivars to tetflupyrolimet. In the first study, tetflupyrolimet was applied at preemergence (PRE) or at the 1- to 2-leaf stage of rice (POST) at 0.1, 0.125, or 0.15 kg ai ha−1 followed by carfentrazone. Tetflupyrolimet provided ≥99% control of watergrass species and 100% bearded sprangletop control regardless of the rate or application timing, while showing no crop injury symptoms or yield reduction. In the second study, tetflupyrolimet was applied PRE or POST at 0.1 or 0.15 kg ai ha−1 followed by herbicides labeled for use in California rice production. Tetflupyrolimet provided ≥98% control of watergrass species, which was better than the grower standard treatment, and ≥97% control of bearded sprangletop. In the third study, tetflupyrolimet was applied PRE or POST at 0.125, 0.15, 0.25, or 0.3 kg ai ha−1 followed by carfentrazone. The six California rice cultivars evaluated, ‘M-105’, ‘M-206’, ‘M-209’, ‘M-211’, ‘L-208’, and ‘CM-203’, did not show any trend of crop injury caused by tetflupyrolimet. Overall, tetflupyrolimet provided a high level of control of watergrass species and bearded sprangletop without causing visual rice injury or yield reductions, regardless of rice cultivar, when applied alone or in combination with commonly used sedge and broadleaf herbicides in California water-seeded rice.

Influence of spray volume on the control of Conyza spp. in soybean pre-sowing with burndown.

The herbicide mixture diclosulam + halauxifen appears to be an alternative for the control of Conyza spp.; however, the spray volume may result in different spray deposition effects on the target and, therefore, on the control. Therefore, the objective of this study was to evaluate the impact of different spray volumes of diclosulam + halauxifen on the control of and damage to the leaf surface of Conyza spp. The experiment was conducted in the field in a randomized block design with four replications. Diclosulam + halauxifen (23.52 g ai ha-1 + 6.32 g ae ha-1) was applied to Conyza spp. at average heights greater than 10 cm, followed by sequential application of glufosinate ammonium (500 g ai ha-1) after 14 days. Different spray volumes (200, 150, 100, 80 and 50 L ha-1) were used. The percentage of droplet coverage was evaluated using hydrosensitive paper and analyzed using DropScan software. After 24 hours of initial application, the leaves were collected for scanning electron microscopy (SEM). Although the different spray volumes did not affect the control, faster necrosis effects were observed at 150 and 200 L ha-1. Moreover, the trichome and stomatal density decreased at a spray volume of 200 L ha-1, indicating greater initial damage at this spray volume. Thus, increased spray spray volumes result in increased spray spray deposition, damage to leaf structures and consequently increased control speed.

Impact of reduced rates of tiafenacil at vegetative growth stages on rice growth and yield

Abstract Tiafenacil is a new nonselective protoporphyrinogen IX oxidase–inhibiting herbicide with both grass and broadleaf activity labeled for preplant application to corn, cotton, soybean, and wheat. Early season rice emergence and growth often coincide in the mid-southern United States with applications of preplant herbicides to cotton and soybean, thereby increasing the opportunity for off-target herbicide movement from adjacent fields. Field studies were conducted to identify any deleterious effects of reduced rates of tiafenacil (12.5% to 0.4% of the lowest labeled application rate of 24.64 g ai ha−1) applied to 1- or 3-leaf rice. Visual injury 1 wk after treatment (WAT) for the 1- and 3-leaf growth stages ranged from 50% to 7% and 20% to 2%, respectively, whereas at 2 WAT these respective ranges were 13% to 2%, and no injury was observed. Tiafenacil applied at those rates had no negative season-long effect because observed early season injury was not manifested as a reduction in rice height 2 WAT or rough rice yield. Application of tiafenacil to crops directly adjacent to rice in its early vegetative stages of growth should be avoided because visual injury will occur. When off-target movement does occur, however, the affected rice should be expected to fully recover with no effect on growth or yield, assuming adequate growing conditions and agronomic/pest management are provided.

Salvage treatments for barnyardgrass (Echinochloa crus-galli) control in rice following simulated failed herbicide application

Abstract Florpyrauxifen-benzyl was commercialized in 2018 to target barnyardgrass and aquatic or broadleaf weeds. Field studies were conducted from 2019 to 2021 in Stoneville, MS, to evaluate barnyardgrass control following a simulated failure of florpyrauxifen-benzyl or other common postemergence rice herbicides. In the first field study, florpyrauxifen-benzyl was applied at 0 and 15 g ai ha–1 to rice at the two- to three-leaf stage to simulate a failed application targeting barnyardgrass. Sequential herbicide treatments included no herbicide and full rates of imazethapyr, quinclorac, bispyribac-Na, and cyhalofop applied 7 or 14 d after florpyrauxifen-benzyl treatment. The second field study was designed to evaluate barnyardgrass control with florpyrauxifen-benzyl following simulated failure of postemergence rice herbicides. Initial herbicide treatments included no herbicide and half rates of imazethapyr, quinclorac, bispyribac-Na, and propanil. Sequential applications at 7 or 14 d after the initial herbicide treatments included florpyrauxifen-benzyl at 0 and 30 g ai ha–1. Results from the first study indicated barnyardgrass control 21 d after final treatment (DAFT) was greater with sequential treatments at 7 compared with 14 d after initial treatment (DA-I) with no initial application of florpyrauxifen-benzyl. Therefore, delaying sequential treatments until 14 d after initial florpyrauxifen-benzyl at 15 g ha–1 allowed barnyardgrass to become too large to control with other rice herbicides. Rough rice yield was reduced in plots where quinclorac application was delayed from 7 to 14 DA-I with no initial application of florpyrauxifen-benzyl. The second study suggested that florpyrauxifen-benzyl application should be delayed 14 d after a herbicide failure. Although no differences in barnyardgrass control 21 DAFT were detected whether florpyrauxifen-benzyl was applied 7 or 14 DA-I of any herbicide utilized, &gt;85% control was only achieved when florpyrauxifen-benzyl application was delayed 14 DA-I. These results demonstrate barnyardgrass control options following simulated failed applications of common rice herbicides.

Growth and fecundity of Palmer amaranth escaping glufosinate in soybean with and without grass competition

Abstract Field experiments were conducted at Clayton and Rocky Mount, North Carolina, during the summer of 2020 to determine the growth and fecundity of Palmer amaranth plants that survived glufosinate with and without grass competition in soybean crops. Glufosinate (590 g ai ha−1) was applied at early postemergence (when Palmer amaranth plants were 5 cm tall), mid-postemergence (7–10 cm), and late postemergence (&gt;10 cm) and at orthogonal combinations of those timings. Nontreated Palmer amaranth was grown in weedy (i.e., intraspecific and grass competition), weed-free in-crop (WFIC), and weed-free fallow (WFNC) conditions for comparisons. No Palmer amaranth plants survived the sequential glufosinate applications and control decreased as the plants were treated at a larger size in both experiments. The apical and circumferential growth rate of Palmer amaranth surviving glufosinate was reduced by more than 44% compared with the WFNC Palmer amaranth. The biomass of Palmer amaranth plants that survived glufosinate was reduced by more than 87% compared with the WFNC Palmer amaranth. The fecundity of Palmer amaranth that survived glufosinate was reduced by more than 70% compared with WFNC Palmer amaranth. Palmer amaranth plants that survived glufosinate were as fecund as the WFIC Palmer amaranth in both experiments in soybean fields. The results prove that despite the significant vegetative growth rate decrease of Palmer amaranth that survived glufosinate, plants can be as fecund as nontreated plants. The trends in growth and fecundity of Palmer amaranth that survives glufosinate with and without grass competition were similar. These results suggest that glufosinate-treated grass weeds may not reduce the growth or fecundity of Palmer amaranth that survives glufosinate.

Non–target site mechanisms of cross-resistance evolution to florpyrauxifen-benzyl in 2,4-D–resistant Palmer amaranth (Amaranthus palmeri)

AbstractThe evolution of herbicide resistance in weeds can reduce the herbicide’s efficacy, depleting crop yield and quality. Our group previously confirmed 2,4-D resistance in three Palmer amaranth (Amaranthus palmeri S. Watson) populations (R1 to R3). In the current study, the first filial (F1) seeds of 2,4-D–resistant populations were subjected to screening tests for resistance to other auxin-mimicking herbicides, florpyrauxifen-benzyl (FPB; 30 g ai ha−1) and dicamba (560 g ae ha−1). Dicamba killed all resistant populations. FPB provided 100% control of only the R3 population. Sensitivities to FPB were reduced by 2 and 35 percentage points in R1 and R2 populations, respectively. Pretreatment with malathion increased FPB sensitivity by 15 percentage points in the R2 population. FPB resistance characterization and mechanism were evaluated using a purified line of the R2 population (F2). The FPB sensitivity was 29-fold lower in the F2 line than in the susceptible (S) standard. Absorption, translocation, and total metabolism of FPB were similar for S and R2 populations. However, less florpyrauxifen-acid (FPA) was detected in the R2 population (17.0% to 25.4%) than in the S population (22.8% to 33.2%), due to its rapid metabolism and/or reduced production with resistance evolution. Because the results of the non–target site resistance mechanism evaluation observed in this study were insufficient to account for the 29-fold reduced sensitivity of the R2 population to FPB, further genetic studies are needed to investigate the presence of target-site resistance in that population.

Evaluation of Amisulbrom Products for the Management of Clubroot of Canola (Brassica napus).

Clubroot, caused by Plasmodiophora brassicae, is an important disease of canola (Brassica napus). Amisulbrom, a quinone inside inhibitor (QiI), was evaluated for its effectiveness in clubroot management in Alberta, Canada. Resting spores of P. brassicae were treated in vitro with 0, 0.01, 0.1, 1, and 10% (w/v) amisulbrom to determine its effect on spore germination and viability. Amisulbrom inhibited resting spore germination by up to 79% and reduced viable spores by 31% relative to the control. Applications of a liquid solution (AL1000, 1000 g active ingredient (ai) ha-1) and granular formulations (AF700, 700 g ai ha-1; AF1000, 1000 g ai ha-1; AF1500, 1500 g ai ha-1) of amisulbrom were tested on the canola cultivars '45H31' (clubroot-susceptible) and 'CS2000' (moderately resistant) under greenhouse conditions and in field experiments in 2019 and 2020. In the greenhouse, the treatments were evaluated at inoculum concentrations of 1 × 105 or 1 × 107 resting spores g-1 soil. A trend of decreasing clubroot severity with an increasing amisulbrom rate was observed. At the lower spore concentration, treatment with AF1500 resulted in a clubroot disease severity index (DSI) <20% for both cultivars, while the lowest DSI under both low and high spore concentrations was obtained with AL1000. The field results indicated a significant reduction in DSI, with varied effects of rates and liquid vs. granular formulations. The greatest reductions (up to 58.3%) in DSI were obtained with AF1500 and AL1000 in 2020. These findings suggest that amisulbrom holds promise as part of an integrated clubroot management approach.

Reduced irrigation impact on soil-applied herbicide dissipation and rotational crop response

Abstract Soil-applied herbicides are important for controlling weeds in many crops but risk damage to susceptible rotational crops if they persist. Field studies were conducted in Powell, WY, from 2015 through 2017 to evaluate the effect of reduced water availability on soil-applied herbicide dissipation. Eight soil-applied herbicides, applied to dry bean or corn, were exposed to three season-long irrigation treatments (100%, 85%, and 70% of estimated crop evapotranspiration [ETc]) by overhead sprinkler. Soil samples were collected to a depth of 10 cm from 0 to 140 d after application, and soil herbicide concentrations were quantified using gas or liquid chromatography and mass spectrometry. Herbicide concentrations were regressed over time to produce a soil half-life estimate for each herbicide and irrigation treatment. Reduced irrigation decreased dry bean yield by up to 77% and corn yield by up to 50%. After adjusting for precipitation, the lowest irrigation treatment received 78% and 76% as much water as the full irrigation treatment in 2015 and 2016, respectively. This significantly increased the soil half-life of imazethapyr but did not increase the soil half-life of atrazine, pyroxasulfone, saflufenacil, ethalfluralin, trifluralin, or pendimethalin. Reduced irrigation did not increase carryover injury to rotational crops from these herbicides 1 yr after application. Instead, carryover response was determined by the inherent persistence of individual herbicides. Imazethapyr (0.1 kg ai ha−1) injured rotational sugar beet, and isoxaflutole (0.1 kg ai ha−1) injured rotational dry bean. Pyroxasulfone (0.2 kg ai ha−1), atrazine (2.0 kg ai ha−1), saflufenacil (0.1 kg ai ha−1) + dimethenamid-P (0.6 kg ai ha−1), ethalfluralin (0.8 kg ai ha−1), trifluralin (0.6 kg ai ha−1), and pendimethalin (1.1 kg ai ha−1) did not injure rotational crops regardless of irrigation treatment. Drought stress sufficient to cause up to 77% crop yield loss did not increase soil-applied herbicide carryover.

Control of Volunteer Glyphosate-Resistant Corn in Soybean With Clethodim Plus Adjuvants

In Ontario, volunteer glyphosate-resistant (GR) corn is one the most common annual grass escapes in GR soybean sprayed with glyphosate. Six field experiments were established in southwestern Ontario during 2021 and 2022 to determine volunteer GR corn control in soybean with glyphosate (900 g ae ha-1) + clethodim (45 g ai ha-1) plus three adjuvants. At 1, 2, and 4 WAA, there was no visible soybean injury from the herbicide treatments evaluated. At 1 WAA, glyphosate + clethodim controlled volunteer GR corn 23%; the addition of the adjuvants Amigo&amp;reg;, Journey HSOC&amp;reg;, and StrikeLock&amp;reg; at 0.5% v/v improved control to 45 to 49%; there was no statistical difference in volunteer corn control among the adjuvants evaluated. At 2 WAA, glyphosate + clethodim controlled volunteer GR corn 23%; the addition of the adjuvants Amigo&amp;reg;, Journey HSOC&amp;reg;, and StrikeLock&amp;reg; at 0.5% v/v improved the control to 73 to 79%; there was no statistical difference in volunteer corn control among the adjuvants evaluated.&amp;nbsp; At 4 WAA, glyphosate + clethodim controlled volunteer GR corn 16%; the addition of the adjuvants Amigo&amp;reg;, Journey HSOC&amp;reg;, and StrikeLock&amp;reg; at 0.5% v/v improved the control to 91 to 95%; there was no statistical difference in volunteer corn control among the adjuvants evaluated. Volunteer corn interference reduced soybean yield by up to 23% in this trial (highest yielding treatment compared to the non-treated control). Reduced volunteer corn interference with clethodim increased soybean yield 13%. Reduced volunteer corn interference with clethodim plus an adjuvant increased soybean yield 27 to 31%. This study concludes that the addition of Amigo&amp;reg;, Journey HSOC&amp;reg;, or StrikeLock&amp;reg; to clethodim improves volunteer GR corn control resulting in a concomitant increase in soybean yield.

Atrazine selectivity for Panicum maximum cv. Massai under no-till and conventional tillage

The objective of this work was to evaluate the effectiveness of atrazine applied in pre-emergence in the control of weeds and its selectivity for forage Panicum maximum cv. Massai in no-till and conventional tillage systems. The experiment was installed in a stripped experimental design, in an 8 x 2 factorial scheme (8 doses of atrazine in 2 planting systems) with three replicates for each treatment. The variables were analyzed and being the presence of phytotoxicity, dry matter accumulation (DM), height of Massai grass plants, and visual evaluation of control effectiveness on weeds. The data were submitted to analysis of variance with the application of the F test, where the control values of 50% of weeds (C50) and a reduction of 50% in the growth of weeds and Massai grass (GR50) were defined. In the no-tillage system the doses for C50 and GR50 of weeds were 944.83 g a.i. ha-1 and 556.39 g a.i. ha-1, respectively. For the conventional planting system, the doses for C50 and GR50 of weeds were 329.52 g a.i. ha-1 and 301.77 g a.i. ha-1, respectively. In both systems, doses below the recommended were able to perform efficient weed control, where the GR50 values of the crop were higher than those of weeds, requiring doses of 1,184.51 g ai ha-1 for no-tillage and 1,632.92 g ia ha-1 for conventional planting.

Growth and yield response of peanut to simulated drift of glufosinate at vegetative and reproductive growth stages

AbstractThe increased incidence of glyphosate-resistant weeds has led to an exponential increase in the use of glufosinate on glufosinate-resistant corn, cotton, and soybean crops. Field experiments were conducted in 2021 and 2022 to evaluate peanut response to glufosinate at 25 and 60 d after planting, corresponding to vegetative (V3) and reproductive (R4) growth stages, at 1.2, 4.7, 18.9, 75.5, and 302 g ai ha−1 representing 1/514 to 1/2 of the labeled rate of 604 g ha−1. Peanut injury and canopy and yield reductions from glufosinate were &lt;10% when applied at 1.2, 4.7, and 18.9 g ha−1. However, at 75.5 and 302 g ha−1 peanut injury ranged from 24% to 72% at the V3 exposure timing and 33% to 54% at the R4 exposure timing. Similarly, glufosinate applied at 75.5 and 302 g ha−1 reduced peanut canopy width by 10% to 23% at the V3 exposure timing and by 43% to 57% at the R4 exposure timing. Averaged across exposure timing, peanut yield was reduced by 15% and 61% when glufosinate was applied at 75.5 and 302 g ha−1, respectively. Averaged across rates, peanut yield reduction was 18% at the V3 exposure timing, with glufosinate at 298 g ha−1 required to cause an estimated 50% reduction in yield. Peanut yield was reduced by 20% when glufosinate was applied at the R3 peanut growth stage, whereas glufosinate applied at 243 g ha-1 caused an estimated 50% reduction in yield. There was no difference in normalized difference vegetative index (NDVI) values between untreated plants and peanut exposed to glufosinate at 1.2, 4.7, and 18.9 g ha−1. However, peanut exposed to glufosinate at 75.5 and 302 g ha−1 was distinguished from untreated plants with lower NDVI values. Based on the Pearson correlation coefficient, the best timing for assessing potential yield reduction based on injury was between 2 and 4 wk after treatment.

Growth dilution and its effect on pesticide dynamics in Okra

Dissipation studies at single and double doses of chlorantraniliprole, thiamethoxam (25 and 50 g ai ha-1), and imidacloprid (20 and 40 g ai ha-1) were conducted on okra fruits following field application, and the residues were estimated using LC-MS/MS. The initial deposit of 0.42 and 0.80 mg kg-1 of chlorantraniliprole dissipated below quantitation level on the tenth day at single and double dosages. For thiamethoxam, the initial deposits of 0.42 and 0.71 mg kg-1 reached below quantitation level on tenth day at single dosage and on fifteenth day at double dosage; and for imidacloprid, the initial deposits are 0.10 and 0.16 mg kg-1 which dissipated below quantification level on fifth day. Growth dilution plays a significant role in the rate of dissipation of thiamethoxam when compared with imidacloprid and chlorantraniliprole when simulated dissipation rate due to growth dilution was calculated. The half-life of chlorantraniliprole, thiamethoxam and imidacloprid were 1.94 and 1.72 days, 1.88 and 1.99 days, 1.13 and 1.05 days, respectively for single and double dosages. Chlorantraniliprole, thiamethoxam and imidacloprid were found to be the safer insecticides with calculated waiting period of less than one day for single dosage.

Influence of fluazifop timing and rate on johnsongrass (Sorghum halepense) control in ACCase-resistant grain sorghum (Sorghum bicolor)

Abstract Genetic similarities between johnsongrass and grain sorghum leave producers with limited herbicide options for postemergence johnsongrass control. TamArkTM grain sorghum with resistance to acetyl-CoA carboxylase-inhibiting herbicides was developed through a collaboration between the University of Arkansas System Division of Agriculture and Texas A&amp;M AgriLife Research. Two field experiments were conducted in 2021 in two locations each: Keiser and Marianna, AR, or Fayetteville and Marianna, AR. The objective of the first was to determine the optimal rate and application timing of fluazifop-butyl for control of natural johnsongrass populations in a noncrop setting, and the objective of the second was to evaluate johnsongrass control and TamArkTM grain sorghum tolerance in response to fluazifop-butyl applied at different timings and rates based on crop growth stage. The highest levels of johnsongrass control occurred when sequential applications of fluazifop-butyl were utilized. All sequential treatments provided at least 80% johnsongrass control at any rate or application timing tested. A single application of fluazifop-butyl provided greater than 90% johnsongrass control when applied at 210 g ai ha−1 to johnsongrass with fewer than 6 leaves. Weed size played a role in achieving high levels of johnsongrass control. Greater than 90% control was achieved when johnsongrass had 6 leaves or fewer at the initial application for the sequential application treatments. A single application of fluazifop-butyl at 105 g ai ha−1 resulted in no more than 82% johnsongrass mortality at any application timing. TamArk™ grain sorghum injury did not exceed 6% at any application timing or rate. It was therefore considered to be safe even if the initial application was made before the 6-leaf crop stage. Because no unacceptable levels of injury were observed with TamArk™ grain sorghum for fluazifop-butyl, johnsongrass size at the time of application should be the most critical aspect for control with this herbicide.

Evaluation of cauliflower genotypes and eco-friendly molecules for management of Diamond back moth, Plutella xylostella (Linnaeus) (Lepidoptera, Yponemeutidae) and their safety to natural enemies

Four late season cauliflower genotypes namely Pusa Snowball 1 (PSB 1), Pusa Snowball K1 (PSB K1), Pusa Snowball K25 (PSB K25) and Plantsman Snowball (PMS) were evaluated for their resistance to Diamond Back Moth (DBM), Plutella xylostella (Linnaeus), during 2018-19. Among the genotypes screened PSB1 and PMS were comparatively less susceptible. Biochemical analyses of leaves from 85 days old healthy plants showed that PMS had higher phenol content (89.9 mg 100g-1) which on par with PSB-1 with 81.43 mg 100g-1 of leaf. This was followed by PSB K25 and PSB K1 with 69.5 and 54.23 mg 100g-1 respectively. The varieties with higher phenol content offered more resistance to DBM. Protein content of the plant showed no correlation with DBM infestation. Foliar application of spinosad (45 % SC @ 56.25 g ai ha-1 +NSKE 2.5 %) recorded a higher reduction (94.40 %) of DBM population over control, with comparatively higher number of syrphids and coccinellids indicating its safety to natural enemies.

Bio-Efficacy of Glyphosate Ammonium 79.2% SG against Weeds in Tea (Camellia sinensis L.) under Mid-hill Conditions of Himachal Pradesh

A field experiment was conducted at the research farm of Department of Tea Husbandry and Technology, CSK HPKV, Palampur, Himachal Pradesh, India during the summer (February–May) and monsoon (June–October) seasons of 2018. The study consists of ten weed control treatments viz. glyphosate ammonium 79.2% SG at 1.089, 2.178 and 4.356 kg ai ha-1, glyphosate ammonium 71% SG at 2.13 kg ai ha-1, paraquat 0.5 kg ha-1, tank mix combination of glyphosate with 2,4-D (Na) at 1.0+0.5 kg ha-1, glyphosate 1.5 kg ha-1, slashing and in-situ mulching of weeds before flowering, weed free and weedy check. Bidens pilosa, Paspalum distichum, Chromolaena adenophorum, Achyranthus aspera and Artemisia sp., were the dominant weeds in both summer and monsoon seasons. Glyphosate ammonium 79.2% SG at 4.356 kg ai ha-1 being at par with glyphosate 1.00 kg+2,4-D (Na) 0.5 kg ha-1 was quite effective in controlling Bidens pilosa, Paspalum distichum, Chromolaena adenophorum, Achyranthus aspera, Lantana camara, Ageratum sp. and Artemisia sp. in tea. Lowest count of other weeds (Hedera helix, Solanum xanthocarpum, Leucas aspera and Cynodon dactylon) was recorded under glyphosate+2,4-D (Na) 1.0 kg +0.5 kg ha-1 and glyphosate ammonium 79.2% at 4.356 kg ai ha-1, being comparable to weed free check. Among different weed control treatments, significantly higher green leaf yield of 3767 and 3690 kg ha-1 with weed index values of 4.29 and 6.25% was recorded with the application of glyphosate 1.0 kg ha-1+2,4-D (Na) 0.5 kg ha-1 and glyphosate ammonium 79.2% at 2.178 kg ai ha-1, respectively which were also statistically similar to weed free check.