Ae Ha-1 Research Articles

Effect of simulated 2,4-D and dicamba drift on strawberry plant and fruit development

Abstract Greenhouse studies were conducted from 2020 to 2021 to evaluate the effect of simulated drift rates of 2,4-D and dicamba on strawberry growth, fruit development and fruit quality in Raleigh, NC. Treatments included 2,4-D choline and dicamba DGA plus Vapor Grip at 1/2x, 1/20x, and 1/200x of the 1x field rate of 1.09 and 0.8 kg ae ha-1, respectively. Treatments were applied to strawberry at three reproductive stages, including bud, flower, and fruit. Averaged across both herbicides, strawberry canopy size was reduced by the 1/2x rate 18, 25, 30, and 36% at 3, 6, 9, and 11 wk after treatment (WAT). The 1/2x rate of both herbicides caused greater injury to strawberry than the 1/20x or 1/200x, with maximum stunting from 2,4-D and dicamba of 54 and 36%, respectively. Fruit pH and SSC increased due to the 1/2x rate of dicamba compared to the 1/20x and 1/200x rates and the nontreated. Treated fruit (across all herbicides) were larger than fruit developing following herbicide application to flowers or buds but were similar to nontreated fruit.

Confirmation of Glyphosate Resistance in Annual Bluegrass (Poa annua) via EPSPS Duplication in a Soybean and Rice Rotation

Abstract Annual bluegrass (Poa annua L.) populations in turfgrass have evolved resistance to several herbicides in the United States (US), but there has been no confirmed resistance from an agricultural field. Recently, glyphosate failed to control a P. annua population found in a field in a soybean [(Glycine max (L.) Merr.] and rice (Oryza sativa L.) rotation in Poinsett County, Arkansas. The present study focused on determining the sensitivity of a putatively-resistant accession (R1) to glyphosate compared with two susceptible accessions (S1 and S2). The experiments included a dose-response study, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy number and expression analysis, and assessment of mutations in EPSPS. Based on the dose-response analysis, R1 required 1,038 g ae ha-1 of glyphosate to cause 50% biomass reduction, whereas S1 and S2 only required 148.2 g and 145.5 g ae ha-1, respectively. The resistant index (RI) was approximately 7-fold relative to the susceptible accessions. Real-time polymerase chain reaction data revealed at least a 15-fold increase in the EPSPS copy number in R1, along with a higher gene expression. No mutations in EPSPS were found. Gene duplication was identified as the main mechanism conferring resistance in R1. The research presented here reports the first incidence of glyphosate resistance in P. annua from an agronomic field crop situation in the US.

Effect of Crimson® NG Adjuvant on Glyphosate Efficacy in Corn

There is limited published data on the impact of the addition of Crimson® NG to glyphosate on weed control efficacy in corn under Ontario environmental conditions. Four field experiments were conducted at the University of Guelph, Ridgetown Campus, Ridgetown, Ontario during 2022 and 2023 with two water sources to evaluate weed control with glyphosate alone and in combination with Crimson® NG. Glyphosate was applied at rates of 900, 1029, or 1221 g ae ha-1, with and without Crimson® NG at 1.0 and 2.5% v/v, using water with 56 ppm (Ridgetown) and 1600 ppm (Plattsville) hardness. Results showed that glyphosate at 900 g ae ha-1 controlled velvetleaf, Powell amaranth, common ragweed, common lambsquarters, barnyardgrass, and giant foxtail 97-100%, independent of water hardness. Neither increased glyphosate rates nor the addition of Crimson® NG significantly improved weed control. No corn injury was observed with all herbicide/adjuvant treatments evaluated. These findings confirm that glyphosate at 900 g ae ha-1 is highly effective for the control of common annual grass and broadleaf weeds. Weed control efficacy with glyphosate was not influenced by water source and there was no improvement in weed control efficacy from increasing the rate of glyphosate or from the addition of Crimson® NG.

Fall or spring aminopyralid applications control Taeniatherum caput-medusae

AbstractMedusahead [Taeniatherum caput-medusae (L.) Nevski] is an invasive winter annual grass of western North American grasslands and rangelands that negatively impacts forage production, wildlife habitat, and ecosystem processes. Growth regulator herbicides, such as aminopyralid, applied in spring reduced invasive annual grass seed viability in greenhouse and California annual grassland experiments. Beginning in fall 2017, we tested combinations of sequential fall (preemergence) and spring (postemergence) aminopyralid applications at low (103 g ae ha−1) and high (206 g ae ha−1) rates at two ecologically distinct sites in the Intermountain West. Preemergence and postemergence aminopyralid applications at low and high rates controlled T. caput-medusae by 76% to 100% the second summer after study initiation. At the Utah site (which is warmer, drier, and more degraded than the Idaho site), the high rate resulted in better control. The first summer, postemergence aminopyralid applications at low and high rates reduced seed viability 47% to 91% compared with nontreated seeds, with the greatest reductions seen in Utah, which was experiencing drought. Across study sites, reduced T. caput-medusae germination in one year was linked to improved control the following year. The Idaho site also had desirable perennial grasses, which we used to investigate non-target effects. In general, there was a correlation between high T. caput-medusae control and higher perennial grass cover, indicating that successful control can make desirable perennial grasses more vigorous in this system. The option of a spring aminopyralid application increases the management window for controlling invasive annual grasses by decreasing seed viability, thereby depleting short-lived seedbanks.

Glyphosate hormesis effects on the vegetative and reproductive development of glyphosate-susceptible and -resistant Conyza sumatrensis biotypes

Low glyphosate doses that produce hormesis may alter the susceptibility to herbicides of weeds or enhance their propagation and dispersal. The objective of this work was to evaluate the hormetic effects of glyphosate on the vegetative, phenological and reproductive development in resistant (R) and susceptible (S) Conyza sumatrensis biotypes. The glyphosate resistance level of biotype R was 11.2-fold compared to the S biotype. Glyphosate doses <11.25 g ae ha−1 induced temporary and permanent hormetic effects for the number of leaves, plant height and dry mass accumulation up to 28 d after application in both R and S biotypes. The S biotype required 15–19% fewer thermal units at 1.4 and 2.8 g ae ha−1 glyphosate than untreated plants to reach the bolting stage. Also, this biotype had less thermal units associated with the appearance (1225 vs 1408 units) and opening (1520 vs 1765 units) of the first capitulum than the R biotype. In addition, glyphosate affected reproductive traits of both biotypes compared to their controls, increasing the number of capitulum's and seeds per plant up to 37 and 41% (at 2.8 and 0.7 g ae h−1, respectively) in the S biotype, and by 48 and 114% (both at 5.6 g ae ha−1) in the R biotype. Depending on environmental parameters, glyphosate may or may not cause hormetic effects on the vegetative and phenological development of C. sumatrenis biotypes; however, this herbicide increases the speed and fecundity of reproduction, regardless of the glyphosate susceptibility level, which can alter the population dynamics and glyphosate susceptibility of future generations.

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.

Enhanced metabolic detoxification is associated with fluroxypyr resistance in Bassia scoparia.

Auxin-mimic herbicides chemically mimic the phytohormone indole-3-acetic-acid (IAA). Within the auxin-mimic herbicide class, the herbicide fluroxypyr has been extensively used to control kochia (Bassia scoparia). A 2014 field survey for herbicide resistance in kochia populations across Colorado identified a putative fluroxypyr-resistant (Flur-R) population that was assessed for response to fluroxypyr and dicamba (auxin-mimics), atrazine (photosystem II inhibitor), glyphosate (EPSPS inhibitor), and chlorsulfuron (acetolactate synthase inhibitor). This population was resistant to fluroxypyr and chlorsulfuron but sensitive to glyphosate, atrazine, and dicamba. Subsequent dose-response studies determined that Flur-R was 40 times more resistant to fluroxypyr than a susceptible population (J01-S) collected from the same field survey (LD50 720 and 20 g ae ha-1, respectively). Auxin-responsive gene expression increased following fluroxypyr treatment in Flur-R, J01-S, and in a dicamba-resistant, fluroxypyr-susceptible line 9,425 in an RNA-sequencing experiment. In Flur-R, several transcripts with molecular functions for conjugation and transport were constitutively higher expressed, such as glutathione S-transferases (GSTs), UDP-glucosyl transferase (GT), and ATP binding cassette transporters (ABC transporters). After analyzing metabolic profiles over time, both Flur-R and J01-S rapidly converted [14C]-fluroxypyr ester, the herbicide formulation applied to plants, to [14C]-fluroxypyr acid, the biologically active form of the herbicide, and three unknown metabolites. The formation and flux of these metabolites were faster in Flur-R than J01-S, reducing the concentration of phytotoxic fluroxypyr acid. One unique metabolite was present in Flur-R that was not present in the J01-S metabolic profile. Gene sequence variant analysis specifically for auxin receptor and signaling proteins revealed the absence of non-synonymous mutations affecting auxin signaling and binding in candidate auxin target site genes, further supporting our hypothesis that non-target site metabolic degradation is contributing to fluroxypyr resistance in Flur-R.

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.

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.

Hormetic Effect Caused by Sublethal Doses of Glyphosate on Toona ciliata M. Roem.

This study aimed to evaluate the response of Toona ciliata seedlings to sublethal doses of glyphosate. The increasing use of glyphosate in agriculture concerns the scientific community, as the drift of this pollutant into aquatic systems or atmospheric currents can affect non-target species. Therefore, we need to understand how non-target species respond to small doses of this herbicide. T. ciliata seedlings (clone BV-1110) were exposed to sublethal doses of glyphosate (0, 9.6, 19.2, 38.4, 76.8 g ae ha-1). Anatomical, physiological, and photochemical analyses were performed 60 days after herbicide application, and growth assessments were carried out after 160 days of cultivation. We found that sublethal doses of glyphosate above 19.2 g ae ha-1 induced toxicity symptoms in Toona ciliata leaves. These symptoms were mild in some cases, such as chlorosis, but severe in other cases, such as tissue necrosis. We observed a positive relationship between increased plant height and photochemical yield with plant exposure to sub-doses 9.6 and 19.2 g ae ha-1. A sublethal dose of 38.4 g ae ha-1 improved the photosynthetic rate and carboxylation efficiency. Thus, we confirmed the hypothesis of a hormetic effect when T. ciliata was exposed to sub-doses of glyphosate equal to or lower than 38.4 g ae ha-1. However, the sublethal dose of 76.8 g ae ha-1 must be considered toxic, impacting photosynthetic activity and, consequently, the height of T. ciliata. The stem diameter of T. ciliata responded positively to increasing glyphosate doses. This occurs to compensate for the negative effect of glyphosate on water absorption. Further research will provide valuable information for harnessing the potential benefits of hormesis to improve the productivity of T. ciliata.

Peach tree response to low dosages of dicamba as repeated application or with various spray nozzles

Abstract Two low-dose dicamba exposure trials were conducted on container-grown peach trees in Fayetteville, AR. Peach trees were ‘July Prince’ scions grafted onto ‘Guardian’ rootstock, were transplanted into 19-L containers, and received experimental dicamba treatments in each year. Container trials were initiated in 2020 and repeated on new trees in 2021. In the repeated application trial, dicamba was applied at 5.6 g ae ha−1 (1/100X field rate) in five sequences: an untreated control receiving no herbicide, one treatment receiving only an initial application, and three treatments receiving an initial application plus sequential applications at the same rate occurring at 14 d, 28 d, and 14 d + 28 d after initial treatment (DAT). A separate trial assessed peach tree responses to dicamba applied at 11.2 g ae ha−1 (1/50X field rate) using a selection of nozzles with differing droplet spectrum characteristics: Turbo TeeJet® induction nozzle TTI11002, air induction turbo TwinJet® nozzle AITTJ60-11002, air induction extended-range (XR) TeeJet® nozzle AIXR11002, XR TeeJet® flat-fan nozzle XR11002, and XR TeeJet® flat-fan nozzle XR1100067. Peach tree height, tree cross-sectional area, and leaf chlorophyll content were not reduced in response to any sequence of dicamba application or nozzle selection. Repeated applications of dicamba at a 1/100X rate did not increase peach injury after 28 DAT. By 84 DAT, no effect of nozzle type on peach tree injury was discernable, and all treatments caused below 4% injury. No dicamba or dicamba metabolites were observed in leaf samples collected at 14, 69, or 85 DAT from trees treated with XR1100067 or in untreated controls. While peach tree injury was observed throughout the experiment, dicamba residues were detected consistently only in 2020 from leaf samples of trees treated with dicamba at a 1/50X rate using TTI1102, AITTJ60-11002, AIXR11002, and XR11002 nozzles.

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.

Investigation of inquiries on weed control efficacy of XtendiMax® herbicide with VaporGrip® technology

AbstractHerbicide resistance in weeds significantly threatens crop production in the United States. The introduction of dicamba-resistant soybean and cotton stacked with other herbicide tolerance traits has provided farmers with the flexibility of having multiple herbicide options to diversify their weed management practices and delay resistance evolution. XtendiMax® herbicide with VaporGrip® Technology is a dicamba formulation registered for use on dicamba-resistant soybean and cotton crops by the U.S. Environmental Protection Agency (EPA). One of the terms of its registration includes an evaluation of inquiries on reduced weed control efficacy by growers or users of XtendiMax for suspected weed resistance. A total of 3,555 product performance inquiries (PPIs) were received from 2018 to 2021 regarding reduced weed control efficacy by dicamba. Following the criteria recommended by EPA for screening of suspected resistance in the field, a total of 103 weed accessions from 63 counties in 13 states were collected for greenhouse testing over those 4 yr. Weed accessions for greenhouse testing were collected only in states where resistance to dicamba was not yet confirmed in the weed species under investigation. The accessions, which consisted primarily of waterhemp and Palmer amaranth, were treated with dicamba at rates of 560 g ae ha−1 and 1,120 g ae ha−1. All weed accessions, except for one accession each of Palmer amaranth and waterhemp, were controlled by ≥90% with dicamba at 21 d after treatment in the greenhouse.

Effect of Class Act NG Adjuvant on Glyphosate Efficacy in Corn

There is little information on the effect of the co-application of glyphosate with Class Act NG adjuvant on weed control efficacy and corn yield under Ontario environmental conditions. This study consisted of 6 field experiments that were conducted in Ontario during 2021 and 2022 to determine if the addition of Class Act NG (2.5% v/v) to glyphosate at 450, 900 and 1350 g ae ha-1 would improve weed control and result in a concomitant increase in corn yield. The co-application of glyphosate with Class Act NG resulted in no visible corn injury at 1 and 4 weeks after herbicide application (WAA). The addition of Class Act NG to glyphosate at 450 g ae ha-1 improved control of common lambsquarters, velvetleaf, Powell amaranth, common ragweed, and barnyardgrass as much as 20, 14, 9, 8, and 7%, respectively but there was no improvement in control of giant foxtail, or green foxtail and there was no increase in corn yield. The addition of Class Act NG to glyphosate at 900 g ae ha-1 improved common lambsquarters control 6 and 5% at 4 and 8 WAA, respectively and improved barnyardgrass control 4% at 4 WAA. The addition of Class Act NG to glyphosate at 1350 g ae ha-1 provided no improvement in control of velvetleaf, Powell amaranth, common ragweed, common lambsquarters, barnyardgrass, giant foxtail, or green foxtail and there was no increase in corn yield. Based on this data the co-application of glyphosate with Class Act NG results in improved control of some annual broadleaf and grass weeds (common lambsquarters, velvetleaf, Powell amaranth, common ragweed and barnyardgrass) when glyphosate is applied at 450 or 900 g ae ha-1; however, when glyphosate is applied at 1350 g ae ha-1 there was no improvement in weed control. The addition of Class Act NG to glyphosate at 450, 900 and 1350 g ae ha-1 did not result in an increase in corn yield.

Evaluation of goosegrass response to combinations of topramezone and chlorothalonil

AbstractFew herbicides are registered for goosegrass control in creeping bentgrass turfgrass. Topramezone controls goosegrass and is labeled for use on creeping bentgrass, but potential injury risks lead many turf managers to frequently apply it at a low-dose. This application practice increases the likelihood that topramezone treatments will be mixed with fungicide treatments. Previous research found that fungicides can reduce the activity of some herbicides, but their effects on topramezone efficacy are unknown. Four studies were established between Blacksburg, VA, and North Brunswick, NJ, in 2021 to determine whether chlorothalonil reduces goosegrass control from topramezone. In controlled environment dose-response studies the amount of topramezone needed to reduce goosegrass biomass by 50% increased from 3.04 g ha−1 to 5.27 g ha−1 when chlorothalonil (7,400 g ha−1) was added to the mixture. In field experiments, topramezone at 3.7 and 6.1 g ha−1 controlled goosegrass by 50% and 63%, respectively, at 42 d after treatment when averaged across herbicide admixtures. The addition of chlorothalonil alone and chlorothalonil plus acibenzolar-S-methyl to topramezone reduced goosegrass control from 73% to 52% and 45%, respectively, when averaged across topramezone rate. From these studies we can conclude that chlorothalonil has the potential to reduce goosegrass control when topramezone is applied at the maximum allowable rate (6 g ae ha−1) or less. This is the first report of fungicides acting to reduce herbicidal weed control efficacy in turfgrass systems.

Smooth scouringrush (Equisetum laevigatum) control with glyphosate is affected by surfactant choice and application time

AbstractSmooth scouringrush is a creeping perennial with a high silica content in stems that may impede herbicide uptake. Smooth scouringrush has become a troublesome weed in no-till cropping systems across eastern Washington. In previous field studies, glyphosate provided inconsistent control of smooth scouringrush. The objective of this study was to determine if the addition of an organosilicone surfactant to glyphosate would improve the efficacy and consistency of control through stomatal flooding. To test this hypothesis, glyphosate was applied at three field sites at 3.78 kg ae ha–1 alone, with an organosilicone surfactant (OS1 or OS2), an organosilicone plus nonionic surfactant blend, or an alcohol-based surfactant applied during the day or at night. Stem counts were recorded 1 yr after herbicide applications. Five of the six effective treatments observed across the three study sites included organosilicone surfactant or an organosilicone plus nonionic surfactant blend. At two sites, when there was a difference in efficacy between application times; daytime applications were more effective than nighttime applications. These results support the hypothesis of stomatal flooding as a likely mechanism for enhanced efficacy of glyphosate with the addition of an organosilicone surfactant. However, at one site, the treatments containing organosilicone surfactant were more efficacious when applied at night than during the day. At this site, high daytime temperatures and low relative humidity may have resulted in rapid evaporation of spray droplets. The addition of an organosilicone surfactant to glyphosate is recommended for smooth scouringrush control, and daytime treatments are preferred but should be applied when temperatures and humidity are not conducive to rapid droplet drying. Further research is necessary to confirm that stomatal flooding is responsible for improved glyphosate efficacy.

Corn Plant Density Effects on Grain Yield and Palmer Amaranth Response to Dicamba

Palmer amaranth (Amaranthus palmeri S. Wats.) is primarily found in fallow and cultivated fields throughout Kansas (KS). Previously, we reported that the effective dose of dicamba for 50% control (ED50) of a 10-30 cm tall A. palmeri accession from KS (KSP) during the fallow-year of a wheat-corn-fallow rotation (WCF) ranged between 40.4 to 283.5 g ae ha-1 Here, we investigated corn (Zea mays L.) plant density effects on grain yield and the KSP response to dicamba in the corn-year of the WCF rotation. The experiments used a randomized complete block design with four replicates and a split-plot arrangement of treatments. Main plots consisted of corn planted at five densities (49,400; 61,700; 74,100; 86,400 and 98,800 plants ha-1) and sub-plots consisted of six doses of dicamba [(70, 140, 210, 280, 420, and 560 g ae ha-1) applied near V6], a weedy-check, and a weed-free check. In general, acceptable grain yield and KSP control with dicamba doses &amp;lt; 560 g ae ha-1 were only achieved when corn was planted at a density &amp;ge; 74,100 plants ha-1. Based on the ED50 estimates, the KSP required 4.4-8.2% less dicamba for height and biomass reduction as corn plant density increased from 49,400 to 98,800 plants ha-1. Conversely, the amount of dicamba required for 50% reduction of KSP density increased 45.1% from 144.4 to 209.6 g ae ha-1 as corn plant density increased from 49,400 to 98,800 plants ha-1, respectively. Taken together, this study shows that integration of high-density corn planting with dicamba is a cost-effective tool for controlling A. palmeri. However, resistance mitigation and a season-long control of this species cannot be achieved without the integration of other more diversified and robust strategies that include the use of preemergence fb postemergence herbicide programs that overlap residuals with cultural, biological, and mechanical weed control tactics.

Hormetic Effect of Glyphosate on the Morphology, Physiology and Metabolism of Coffee Plants.

Glyphosate is a nonselective herbicide of systemic action that inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase, thus compromising amino acid production and consequently the growth and development of susceptible plants. The objective of this study was to evaluate the hormetic effect of glyphosate on the morphology, physiology, and biochemistry of coffee plants. Coffee seedlings (Coffea arabica cv Catuaí Vermelho IAC-144) were transplanted into pots filled with a mixture of soil and substrate and subjected to ten doses of glyphosate: 0, 11.25, 22.5, 45, 90, 180, 360, 720, 1440, and 2880 g acid equivalent (ae) ha-1. Evaluations were performed using the morphological, physiological, and biochemical variables. Data analysis for the confirmation of hormesis occurred with the application of mathematical models. The hormetic effect of glyphosate on coffee plant morphology was determined by the variables plant height, number of leaves, leaf area, and leaf, stem, and total dry mass. Doses from 14.5 to 30 g ae ha-1 caused the highest stimulation. In the physiological analyses, the highest stimulation was observed upon CO2 assimilation, transpiration, stomatal conductance, carboxylation efficiency, intrinsic water use efficiency, electron transport rate, and photochemical efficiency of photosystem II at doses ranging from 4.4 to 55 g ae ha-1. The biochemical analyses revealed significant increases in the concentrations of quinic acid, salicylic acid, caffeic acid, and coumaric acid, with maximum stimulation at doses between 3 and 140 g ae ha-1. Thus, the application of low doses of glyphosate has positive effects on the morphology, physiology, and biochemistry of coffee plants.

Sensitivity of eucalyptus (Eucalyptus urograndis) plants to subdoses of the herbicide dicamba

In view of the widespread increase in herbicide-resistant weeds, biotechnology companies have developed dicamba-tolerant soybean and cotton cultivars. This technology can, however, increase the risk of the product drifting to adjacent areas. This study was developed with the objective of the to evaluate the phytotoxicity and biometric variables of young eucalyptus plants exposed to subdoses of the herbicide dicamba. The experiment was carried out under field conditions in Rio Verde, state of Goiás, Brazil. The treatments were represented by the application of 0 (control), 7.5, 15, 30, 60, 120 or 240 g ae ha-1 of dicamba 45 days after the seedlings were planted in the field. In terms of phytotoxicity, the dicamba doses of 120 and 240 g ae ha-1 caused greater damage to the eucalyptus plants in all periods of evaluation. The predominant symptoms were epinasty, increased number of shoots and necrosis and senescence of young branches and leaves. The herbicide doses of 120 and 240 g ae ha-1 significantly compromised plant height and diameter, number of branches and dry mass of leaves and roots, interfering with the growth and development of the eucalyptus crop. The results indicate that the effect of subdoses of the herbicide dicamba can interfere with the proper development of young eucalyptus plants, which may cause losses in the initial planting phase and future losses for producers.

American frogbit response to herbicides

Limnobium spongia (frogbit) is a free-floating aquatic plant that can produce extensive floating mats causing negative ecological, social, and economic impacts that can harm aquatic fauna (i.e., dissolved oxygen depletion) and restrict human uses of water. Literature describing effective control measures for frogbit is minimal. Efficacy of high and low doses of seven foliar-applied herbicides (2,4-D, florpyraux-ifen-benzyl, flumioxazin, glyphosate, imazamox, imazapyr, and triclopyr) were evaluated in a mesocosm setting in the summers of 2018, 2020, and 2021. Both emergent and submersed frogbit biomass were reduced at least 99% by imazamox (0.56 and 1.11 kg ai ha􀀁1) and imazapyr (0.42 and 0.84 kg ae ha􀀁1) 8 wk after treatment (WAT) compared with nontreated reference plants. Triclopyr (6.71 kg ae ha􀀁1) reduced frogbit biomass 92% and flumioxazin (0.42 kg ai ha􀀁1) reduced biomass 87 to 93% compared with reference plants. 2,4-D (2.12 and 4.24 kg ae ha􀀁1), glyphosate (2.83 and 5.67 kg ai ha􀀁1), triclopyr (3.36 kg ae ha􀀁1), florpyrauxifen-benzyl (0.02 and 0.05 kg ai ha􀀁1), and flumioxazin (0.21 kg ai ha􀀁1) did not reduce frogbit biomass 8 WAT compared with reference plants. Future research should consider the efficacy of different herbicide combinations to control frogbit, as well as the role of diluent volume per unit area, especially with imazamox and imazapyr. Field studies also will be useful in determining whether the results observed in this study will translate to management of frogbit in natural settings.