Belowground microbial communities respond to water deficit and are shaped by decades of maize hybrid breeding.

Root-associated microbial communities are important for maintaining agricultural productivity. However, belowground microbial community response to drought in temperate maize agroecosystems, as well as how these responses to water-stress are shaped by host genotype are poorly understood. Ten maize hybrids (six newer and four older) were grown in a replicated field trial. The endosphere, rhizosphere and soil bacterial and archaeal communities were sampled and analyzed using 16S rRNA gene amplicon sequencing. Sampling was done at two developmental stages in a water-limited environment with and without supplemental irrigation. Significant shifts in microbial community composition (ß-diversity) were measured between two sampling times during the season, in well-watered and water-stressed conditions and in newer and older generation maize hybrids. The microbial community diversity within samples (α-diversity) was not affected by drought stress or host factors. The phyla Actinobacteria and Firmicutes were more abundant in the rhizosphere of newer hybrids under water stress. These results highlight the importance of temporal variation, environmental stress and plant genetics as influenced by breeding history in shaping the composition of root associated microbial communities. These insights may provide new approaches to the improvement of crop stress tolerance through optimizing microbial communities.

Factors Affecting the Development and Severity of Goss's Bacterial Wilt and Leaf Blight of Corn, Caused by Clavibacter michiganensis subsp. nebraskensis.

Goss's bacterial wilt and leaf blight, which is caused by Clavibacter michiganensis subsp. nebraskensis, is a disease of corn (Zea mays) that has been increasingly reported across the Midwest since its reemergence in western Nebraska, northeastern Colorado, and southeastern Wyoming during the 2006 growing season. The objective of this study was to identify environmental and agronomic factors contributing to the incidence of the disease across the Corn Belt through a multistate survey conducted during the 2011 growing season. Of the 2,400 surveys distributed throughout nine states, 486 were returned with corn leaf samples, of which 70% tested positive for C. michiganensis subsp. nebraskensis using an enzyme-linked immunosorbent assay. The agronomic data associated with each field were analyzed using classification and regression tree and random forest analyses to identify the factors that contributed most to Goss's bacterial wilt and leaf blight development. A χ2 test of independence was also done to determine relationships between certain variables and disease incidence. The two best predictors of Goss's bacterial wilt and leaf blight were hybrid resistance to Goss's bacterial wilt and leaf blight, as indicated by the seed companies' score and a planting population density >67,500 plants ha-1. Other important predictors included longitude, planting date, crop rotation, percent residue, yield history, tillage, and growth stage. Relationships between glyphosate applications, foliar fungicide applications, and corn rootworm beetle with samples testing positive for C. michiganensis subsp. nebraskensis were also detected. These data contribute to our understanding of factors that increase the risk of Goss's bacterial wilt and leaf blight, and should enable more effective management practices to be adopted or developed.

Introgression of novel traits from a wild wheat relative improves drought adaptation in wheat.

Root architecture traits are an important component for improving water stress adaptation. However, selection for aboveground traits under favorable environments in modern cultivars may have led to an inadvertent loss of genes and novel alleles beneficial for adapting to environments with limited water. In this study, we elucidate the physiological and molecular consequences of introgressing an alien chromosome segment (7DL) from a wild wheat relative species (Agropyron elongatum) into cultivated wheat (Triticum aestivum). The wheat translocation line had improved water stress adaptation and higher root and shoot biomass compared with the control genotypes, which showed significant drops in root and shoot biomass during stress. Enhanced access to water due to higher root biomass enabled the translocation line to maintain more favorable gas-exchange and carbon assimilation levels relative to the wild-type wheat genotypes during water stress. Transcriptome analysis identified candidate genes associated with root development. Two of these candidate genes mapped to the site of translocation on chromosome 7DL based on single-feature polymorphism analysis. A brassinosteroid signaling pathway was predicted to be involved in the novel root responses observed in the A. elongatum translocation line, based on the coexpression-based gene network generated by seeding the network with the candidate genes. We present an effective and highly integrated approach that combines root phenotyping, whole-plant physiology, and functional genomics to discover novel root traits and the underlying genes from a wild related species to improve drought adaptation in cultivated wheat.

Particle drift simulation from mesotrione and rimsulfuron plus thifensulfuron-methyl mixture through two nozzle types to field and vegetable crops.

Potential for off-target movements follows every herbicide application. Because the launch of acetolactate synthase (ALS)- and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide-tolerant crops will increase the treated area, there is a need to assess the possible negative consequences of any particle drift from those herbicides. Drift happens with every pesticide application, requiring mitigation. Various factors influence drift. Some, such as nozzle type, working pressure, and boom height, can be managed. Others, such as wind, are not easy to manage. In our study, an herbicide tank mixture of mesotrione with rimsulfuron plus thifensulfuron-methyl was sprayed in a low-speed wind tunnel to simulate drift. The airspeed was set at 4.4 m s-1, representing the labeled upper limit for applications. The herbicide solution was sprayed through XR110015 and TTI110015 nozzles. Eight crops were exposed to herbicide drift treatments and biomass data were collected. Droplet size spectra and tracer depositions were evaluated. Tracer deposition was on average threefold higher in all downwind distances (0.5, 1, 2, 3, 4, 6, 9, and 12 m) from the XR nozzle in comparison to the TTI nozzle. As a consequence, greater biomass reduction was recorded for applications with the XR compared to the TTI nozzle from 1 to 12 m downwind. At 12-m distance, biomass was decreased by 7-78% using XR nozzle while 1-27% using the TTI nozzle. Because drift can injure crops, it is very important to mitigate drift from application of formulations containing mesotrione and rimsulfuron plus thifensulfuron-methyl in combination. This can be done by selecting the appropriate nozzle and ensuring optimal distances between crops.

Spray drift potential of dicamba plus S-metolachlor formulations.

BACKGROUND: Early-postemergence herbicide applications in the USA often include residual herbicides such as S-metolachlor to suppress late late-emerging Amaranthus spp. Although this practice benefits weed control, herbicide tankmixes can influence spray droplet size and drift potential during applications. The addition of S-metolachlor products to dicamba spray solutions generally decreases spray droplet size and increases spray drift potential. Advances in formulation technology fostered the development of products with reduced spray drift potential, especially for herbicide premixes containing multiple active ingredients. The objective of this study was to compare the drift potential of a novel dicamba plus S-metolachlor premix formulation (capsule suspension) against a tankmix containing dicamba (soluble liquid) and S-metolachlor (emulsifiable concentrate) using different venturi nozzles. RESULTS: The MUG nozzle had greater DV0.5 (1128.6 µm) compared to the ULDM (930.3 µm), TDXL-D (872.9 µm), and TTI nozzles (854.8 µm). The premix formulation had greater DV0.5 (971.0 µm) compared to the tankmix (922.3 µm). Nozzle influenced spray drift deposition (P < 0.0001) and soybean biomass reduction (P = 0.0465). Herbicide formulation influenced spray drift deposition (P < 0.0001), and biomass reduction of soybean (P < 0.0001) and cotton (P = 0.0479). The novel capsule suspension formulation (premix) of dicamba plus S-metolachlor had reduced area under the drift curve (AUDC) (577.6) compared to the tankmix (913.7). Applications using the MUG nozzle reduced AUDC (459.9) compared to the other venturi nozzles (ranging from 677.4 to 1141.7). CONCLUSION: Study results evidence that advances in pesticide formulation can improve pesticide drift mitigation. © 2021 Society of Chemical Industry.

Soybean dose-response to 2,4-D and dicamba at vegetative and reproductive growth stages.

BACKGROUND: Field experiments were conducted across multiple sites in 2012 and 2013 to describe sensitivity of soybean to 2,4-D (six doses) and dicamba (seven doses) at V3 and R1 growth stages. Further experiments were conducted under greenhouse conditions in 2017 and 2018 to compare soybean response to several dicamba herbicides across a broader range of doses than those tested in the field. RESULTS: Soybean yield loss was 6.1-fold greater from 2,4-D exposure at V3 compared to R1 and 1.4 times greater from dicamba exposure at R1 than at V3. In V3 exposures, soybean was 15.4 times more sensitive to dicamba than 2,4-D and 134.4-fold more sensitive to dicamba when exposed at R1. Plant injury and height correlations to grain yield resulted in coefficients ranging from 0.65 to 0.91. In greenhouse experiments, five dicamba products were tested at up to 19 doses and as low as 0.002 g ae ha-1 (3.6 × 10-6 % of maximum single use-rate); however, no differences were observed among formulations used in dicamba-resistant crops versus traditional formulations. A no observable effects dose was not identified due to responses observed even at the lowest doses tested, although hormesis effects were observed in plant height. CONCLUSION: These data suggest that the sensitivity of soybean to dicamba is much greater than what has previously been reported. However, as has been indicated by previous work, that injury does not always result in yield loss. © 2022 Society of Chemical Industry.

Hooded broadcast sprayer for particle drift reduction.

BACKGROUND: There is renewed interest amongst crop protection professionals and regulators in the adoption of spray hoods to further reduce pesticide off-target movement during applications. Although the benefits of sprayer hoods have been reported since the early 1950s, adoption has been relatively low among farmers and applicators. The objective of this study was to evaluate the effectiveness of spray hoods in reducing pesticide drift of spray solutions from nozzles typically used for herbicide applications in row crops with tolerance to dicamba or 2,4-D. RESULTS: Hooded applications substantially reduced spray drift potential across all treatment scenarios compared to conventional applications. Hooded applications using the AIXR nozzle without drift-reducing adjuvant (DRA) had a similar area under the drift curve (31.5) compared to conventional applications (open sprayer) using the TTI nozzle with DRA (27.7), despite the major droplet size differences between these treatments (DV50  = 447.5 and 985 µm, respectively). CONCLUSION: These results indicate that the adoption of spray hoods combined with proper nozzle selection, and the use of DRAs can substantially reduce spray drift potential during pesticide applications. The use of this technology can be complementary to other drift-reducing technologies. © 2021 Society of Chemical Industry.

Spray drift deposition comparison of fluorimetry and analytical confirmation techniques.

Tracer dyes are often used as surrogates to characterize pesticide spray drift and it is assumed that they accurately reflect analytical measurement of active ingredients; however, the validity of this assumption remains inconclusive. Consequently, the influence of measurement technique on the magnitude of deposition of spray drift was investigated using spray drift samples evaluated by traditional analytical techniques (HPLC-MS/MS) and fluorimetry (1,3,6,8-pyrene-tetra sulfonic acid tetrasodium salt dye tracer). The experiment was conducted in a low-speed wind tunnel under controlled meteorological conditions. The herbicide mesotrione was sprayed through three spray air induction nozzles (anvil deflector flat fan TTI11004; flat fan AI11004; flat fan AIXR11003). Spray drift deposition samples were collected using stainless steel discs pairs placed side by side in the center of the wind tunnel at distances of 5, 10, 20, 30, and 40 ft (1.5, 3.1, 6.1, 9.1, and 12.2 m) from the spray nozzle. The analytical technique determined pesticide concentration on one disc per pair, and the other was evaluated by fluorimetry. The experimental results, analyzed using the linear split-split plot model, revealed that median deposition concentrations were 15% higher using the tracer dye fluorescence method relative to the analytical method, potentially due in part to procedural recovery inefficiencies of the analytical method (the mean overall procedural recovery result and RSD was 87% ± 6.4% (n = 12). This relationship was consistent and held true for the three nozzle types at all distances within the wind tunnel. © 2021 Society of Chemical Industry.

Effect of carrier volume and spray quality on glyphosate-resistant soybean response to sublethal dicamba exposure.

BACKGROUND: Field experiments were conducted across three sites in Mississippi in 2018 to evaluate carrier volume and spray quality effects on glyphosate-resistant soybean response to dicamba. Treatments consisted of dicamba (5.6 g a.e. ha-1 ) plus glyphosate (8.7 g a.e. ha-1 ) applied to soybean at R1 using 140, 105, 70, 35, 14, or 7 L ha-1 . Each carrier volume was applied with TT11002 and XR110015 nozzles which resulted in Fine and Coarse spray qualities, respectively. A colorimetric dye was included in spray solutions to quantify spray coverage of each treatment. RESULTS: Spray coverage decreased with carrier volume and ranged from 21% to 3%. Conversely, soybean injury increased as carrier volume decreased. Soybean height 14 days after treatment (DAT) was reduced 34% to 37% from carrier volumes of 70 to 140 L ha-1 ; however, carrier volumes of 14 and 7 L ha-1 resulted in 45% height reductions. By 28 DAT soybean height was similar among volumes of 35 to 140 L ha-1 (39% to 42% reduction); however, volumes of 14 and 7 L ha-1 resulted in 46% and 51% reductions, respectively. Grain yield was reduced 14% from treatment at 140 L ha-1 and reductions increased with decreased carrier volume to 41% loss at 7 L ha-1 . Averaged across carrier volumes, Fine and Coarse sprays caused 30% and 26% yield loss, respectively. CONCLUSION: These data suggest that carrier volume profoundly affects soybean response to dicamba. Therefore, soybean response to sublethal dicamba doses applied at a constant carrier volume may not reflect physical drift exposure. © 2021 Society of Chemical Industry.

Conversations about the Future of Dicamba: The Science Behind Off-Target Movement.

Dicamba is an important herbicide for controlling post-emergent resistant weeds in soybean farming. Recently, the scientific community and general public have further examined off-target transport mechanisms (e.g., spray drift, volatilization, and tank contamination) and the visual responses of soybeans to ultralow dicamba concentrations. This paper synthesizes key chemical concepts and environmental processes associated with dicamba formulations, transport mechanisms, drift measurements, and plant responses. This paper proposes additional areas of research and actions to increase our understanding and communicate the science findings, which should provide farmers with more robust tools and practices for sustainable dicamba use.

Herbicide drift exposure leads to reduced herbicide sensitivity in Amaranthus spp.

While the introduction of herbicide tolerant crops provided growers new options to manage weeds, the widespread adoption of these herbicides increased the risk for herbicide spray drift to surrounding vegetation. The impact of herbicide drift in sensitive crops is extensively investigated, whereas scarce information is available on the consequences of herbicide drift in non-target plants. Weeds are often abundant in field margins and ditches surrounding agricultural landscapes. Repeated herbicide drift exposure to weeds could be detrimental to long-term management as numerous weeds evolved herbicide resistance following recurrent-selection with low herbicide rates. The objective of this study was to evaluate if glyphosate, 2,4-D, and dicamba spray drift could select Amaranthus spp. biotypes with reduced herbicide sensitivity. Palmer amaranth and waterhemp populations were recurrently exposed to herbicide drift in a wind tunnel study over two generations. Seeds from survival plants were used for the subsequent rounds of herbicide drift exposure. Progenies were subjected to herbicide dose-response studies following drift selection. Herbicide drift exposure rapidly selected for Amaranthus spp. biotypes with reduced herbicide sensitivity over two generations. Weed management programs should consider strategies to mitigate near-field spray drift and suppress the establishment of resistance-prone weeds on field borders and ditches in agricultural landscapes.

Droplet size and physicochemical property effects on herbicide efficacy of pre-emergence herbicides in soybean (Glycine max (L.) Merr).

BACKGROUND: Unlike post-emergence herbicides (POSTs), little is known about droplet size effect on pre-emergence herbicide (PRE) efficacy. Four nozzle types were used to apply different PRE herbicides on eight soybean fields in Missouri and Mississippi in 2017 and 2018, respectively. Pendimethalin, metribuzin, clomazone, imazethapyr and pyroxasulfone were selected based on their physicochemical characteristics (adsorption, volatility and solubility) and were sprayed using XR11002, ULD12002, TTI6011002, and TTI11002 nozzles. RESULTS: The XR nozzle produced the smallest droplet size (DV0.5 ), 204 µm, followed by the ULD, TTI60 and TTI with DV0.5 of 468, 646, and 794 µm, respectively. Droplet size, spray coverage, nozzle type or physicochemical characteristics showed no effect on PRE herbicide efficacy, except in the Monroe County, MS, field, with pendimethalin. The TTI60 twin fan nozzle enhanced pendimethalin weed control (up to 91%) in comparison with pendimethalin sprayed with the TTI nozzle (64%), in a high organic matter (OM) soil composed of large soil clods and high weed pressure. It was hypothesized that improved herbicide penetration assisted by the TTI60 dual fan pattern increased herbicide-moisture contact and clod coverage by the herbicide. Under soils with higher OM content (>2%) pendimethalin weed control was reduced. In soils with low OM (<0.7%), low cation exchange capacity (CEC) (<13.1%) and rainfall of 12.2 mm within 3 days after application, metribuzin also resulted in reduced weed control. CONCLUSION: The results indicate that droplet size does not affect PRE herbicide efficacy regardless of physicochemical herbicide properties including adsorption, volatility and solubility. © 2019 Society of Chemical Industry.

Maize genomes to fields (G2F): 2014-2017 field seasons: genotype, phenotype, climatic, soil, and inbred ear image datasets.

OBJECTIVES: Advanced tools and resources are needed to efficiently and sustainably produce food for an increasing world population in the context of variable environmental conditions. The maize genomes to fields (G2F) initiative is a multi-institutional initiative effort that seeks to approach this challenge by developing a flexible and distributed infrastructure addressing emerging problems. G2F has generated large-scale phenotypic, genotypic, and environmental datasets using publicly available inbred lines and hybrids evaluated through a network of collaborators that are part of the G2F's genotype-by-environment (G × E) project. This report covers the public release of datasets for 2014-2017. DATA DESCRIPTION: Datasets include inbred genotypic information; phenotypic, climatic, and soil measurements and metadata information for each testing location across years. For a subset of inbreds in 2014 and 2015, yield component phenotypes were quantified by image analysis. Data released are accompanied by README descriptions. For genotypic and phenotypic data, both raw data and a version without outliers are reported. For climatic data, a version calibrated to the nearest airport weather station and a version without outliers are reported. The 2014 and 2015 datasets are updated versions from the previously released files [1] while 2016 and 2017 datasets are newly available to the public.

Rapid metabolism increases the level of 2,4-D resistance at high temperature in common waterhemp (Amaranthus tuberculatus).

Common waterhemp emerges throughout the crop growing season in the Midwestern United States, and as a result, the seedlings are exposed to a wide range of temperature regimes. Typically, 2,4-D is used in the Midwest to control winter annual broad-leaf weeds before planting soybean and in an early post-emergence application in corn and sorghum; however, the evolution of 2,4-D-resistant common waterhemp in several Midwestern states may limit the use of 2.4-D for controlling this problem weed. Moreover, temperature is one of the crucial factors affecting weed control efficacy of 2,4-D. This research investigated the effect of temperature on efficacy of 2,4-D to control 2,4-D susceptible (WHS) and -resistant (WHR) common waterhemp. Do se-response of WHS and WHR to 2,4-D was assessed at two temperature regimes, high (HT; 34/20 °C, d/n) and low (LT; 24/10 °C, d/n). Whole plant dose response study indicated an increased level of 2,4-D resistance in WHR at HT compared to LT. Additional investigation of the physiological mechanism of this response indicated that both WHS and WHR common waterhemp plants rapidly metabolized 14C 2,4-D at HT compared to LT. In conclusion, a rapid metabolism of 2,4-D conferred increased level of resistance to 2,4-D in WHR at HT. Therefore, application of 2,4-D when temperatures are cooler can improve control of 2,4-D resistant common waterhemp.

Response of Amaranthus spp. following exposure to sublethal herbicide rates via spray particle drift.

The adverse consequences of herbicide drift towards sensitive crops have been extensively reported in the literature. However, little to no information is available on the consequences of herbicide drift onto weed species inhabiting boundaries of agricultural fields. Exposure to herbicide drift could be detrimental to long-term weed management as several weed species have evolved herbicide-resistance after recurrent selection with sublethal herbicide rates This study investigated the deposition of glyphosate, 2,4-D, and dicamba spray particle drift from applications with two different nozzles in a low speed wind tunnel, and their impact on growth and development of Amaranthus spp. Herbicide drift resulted in biomass reduction or complete plant mortality. Inflection points (distance to 50% biomass reduction) for Amaranthus tuberculatus were 7.7, 4.0, and 4.1 m downwind distance for glyphosate, 2,4-D, and dicamba applications with the flat-fan nozzle, respectively, whereas these values corresponded to 2.8, 2.5, and 1.9 m for applications with the air-inclusion nozzle. Inflection points for Amaranthus palmeri biomass reduction were 16.3, 10.9, and 11.5 m for glyphosate, 2,4-D, and dicamba applications with the flat-fan nozzle, respectively, whereas these values corresponded to 7.6, 5.4, and 5.4 m for applications with the air-inclusion nozzle. Plants were more sensitive to glyphosate at higher exposure rates than other herbicides, whereas plants were more sensitive to 2,4-D and dicamba at lower exposure rates compared to glyphosate. Applications with the flat-fan nozzle resulted in 32.3 and 11.5% drift of the applied rate at 1.0 and 3.0 m downwind, respectively, whereas the air-inclusion nozzle decreased the dose exposure in the same distances (11.4 and 2.7%, respectively). Herbicide drift towards field boundaries was influenced by nozzle design and exposed weeds to herbicide rates previously reported to select for herbicide-resistant biotypes.

Western corn rootworm pyrethroid resistance confirmed by aerial application simulations of commercial insecticides.

The western corn rootworm (Diabrotica virgifera virgifera LeConte) (WCR) is a major insect pest of corn (Zea mays L.) in the United States (US) and is highly adaptable to multiple management tactics. A low level of WCR field-evolved resistance to pyrethroid insecticides has been confirmed in the US western Corn Belt by laboratory dose-response bioassays. Further investigation has identified detoxification enzymes as a potential part of the WCR resistance mechanism, which could affect the performance of insecticides that are structurally related to pyrethroids, such as organophosphates. Thus, the responses of pyrethroid-resistant and -susceptible WCR populations to the commonly used pyrethroid bifenthrin and organophosphate dimethoate were compared in active ingredient bioassays. Results revealed a relatively low level of WCR resistance to both active ingredients. Therefore, a simulated aerial application bioassay technique was developed to evaluate how the estimated resistance levels would affect performance of registered rates of formulated products. The simulated aerial application technique confirmed pyrethroid resistance to formulated rates of bifenthrin whereas formulated dimethoate provided optimal control. Results suggest that the relationship between levels of resistance observed in dose-response bioassays and actual efficacy of formulated product needs to be further explored to understand the practical implications of resistance.

Winds of change, developing a non-target plant bioassay employing field-based pesticide drift exposure: A case study with atrazine.

A field-scale, spray drift study with atrazine was conducted to simultaneously measure spray drift deposition, airborne interception and corresponding biological effects on two sensitive plant species (cucumber and lettuce). Applications of AAtrex 4L (atrazine) were made using ultra-coarse nozzles (TeeJet TTI11004) under worst-case drift potential conditions of bare soil and high wind speeds (i.e. >10 mph; >16 kph). This study was replicated 4 times, each with two parallel spray swaths (92.5 ft or 28 m per swath) perpendicular to wind direction. Within each replicate application, three sampling lines were used to measure drift deposition (using stainless-steel discs) at distances out to 400 ft (122 m), airborne interception (using stainless-steel rods) at distances out to 75 ft (23 m), and potential direct plant effects at 5, 15, 25, 35, and 45 ft (1.5, 4.6, 7.6, 10.7, and 13.7 m) from the downwind edge of the spray swath. Corresponding upwind control discs and plants were also included in each replicate. Each replicate application targeted steady wind speeds between 10 and 15 mph (16 and 24 kph) within a 30-degree angle of the downwind field orientation. On average, each 10% increase in distance from the spray zone resulted in approximately 14% less ground-deposited atrazine. Between 7 and 41× more atrazine mass was collected from vertical rods (airborne drift), compared to horizontally placed stainless-steel discs (ground deposition). Cucumber and lettuce plants exposed to spray drift were monitored for biological effects over 21 days post-application according to standard protocols. Endpoints of survival, weight (biomass), and shoot length were evaluated by comparing distance groups to up-wind controls. Overall, when trials were combined, the aggregate lowest observable effect distance (LOED) was 5-ft (1.5 m) and the aggregate no observable effects distance (NOED) was 15-ft (4.6 m), with cucumbers affected more than lettuce.

Evaluation of spray pattern uniformity using three unique analyses as impacted by nozzle, pressure, and pulse-width modulation duty cycle.

BACKGROUND: The increasing popularity of pulse-width modulation (PWM) sprayers requires that application interaction effects on spray pattern uniformity be completely understood to maintain a uniform overlap of spray, thereby reducing crop injury potential and maximizing coverage on target pests. The objective of this research was to determine the impacts of nozzle type (venturi vs. non-venturi), boom pressure, and PWM duty cycle on spray pattern uniformity. Research was conducted using an indoor spray patternator located at the University of Nebraska-Lincoln in Lincoln, NE, USA. Coefficient of variation (CV), root mean square error (RMSE), and average percent error (APE) were used to characterize spray pattern uniformity. RESULTS: Generally, across nozzles and pressures, the duty cycle minimally impacted the CV of spray patterns. However, across nozzles and duty cycles, increasing pressure decreased CV values, resulting in more uniform spray patterns. The RMSE values typically increased as pressure and duty cycle increased across nozzles. This may be the result of a correlation between RMSE values and flow rate as RMSE values also increased as nozzle orifice size increased. Generally, APE increased as the duty cycle decreased across nozzles and pressures with significant increases (40%) caused by the 20% duty cycle. Within non-venturi nozzles, increasing pressure reduced APE across duty cycles, while venturi nozzles followed no such trend. CONCLUSION: Overall, results suggest PWM duty cycles at or above 40% minimally impact spray pattern uniformity. Further, increased application pressures and the use of non-venturi nozzles on PWM sprayers increase the precision and uniformity of spray applications. © 2019 Society of Chemical Industry.

Effect of insecticide formulation and adjuvant combination on agricultural spray drift.

Loss of crop protection products when agricultural spray applications drift has economic and ecological consequences. Modification of the spray solution through tank additives and product formulation is an important drift reduction strategy that could mitigate these effects, but has been studied less than most other strategies. Therefore, an experimental field study was conducted to evaluate spray drift resulting from agricultural ground applications of an insecticide formulated as a suspension concentrate (SC) and as a wettable powder (WP), with and without two adjuvants. Droplet sizes were also measured in a wind tunnel to determine if indirect methods could be substituted for field experimentation to quantify spray drift from these technologies. Results suggest that spray drift was reduced by 37% when comparing the SC to the WP formulation. As much as 63% drift reduction was achieved by incorporating certain spray adjuvants, but this depended on the formulation/adjuvant combination. The wind tunnel data for droplet spectra showed strong agreement with field deposition trends, suggesting that droplet statistics could be used to estimate drift reduction of spray solutions. These findings can be used to develop a classification scheme for formulated products and tank additives based on their potential for reducing spray drift.

Bifenthrin Baseline Susceptibility and Evaluation of Simulated Aerial Applications in Striacosta albicosta (Lepidoptera: Noctuidae).

Striacosta albicosta (Smith) is a maize pest that has recently expanded its geographical range into the eastern United States and southeastern Canada. Aerial application of pyrethroids, such as bifenthrin, has been a major practice adopted to manage this pest. Reports of field failure of pyrethroids have increased since 2013. Striacosta albicosta populations were collected in 2016 and 2017 from maize fields in Nebraska, Kansas, and Canada and screened with bifenthrin active ingredient in larval contact dose-response bioassays. Resistance ratios estimated were generally low in 2016 (1.04- to 1.32-fold) with the highest LC50 in North Platte, NE (66.10 ng/cm2) and lowest in Scottsbluff, NE (50.10 ng/cm2). In 2017, O'Neill, NE showed the highest LC50 (100.66 ng/cm2) and Delhi, Canada exhibited the lowest (6.33 ng/cm2), resulting in a resistance ratio variation of 6.02- to 15.90-fold. Implications of bifenthrin resistance levels were further investigated by aerial application simulations. Experiments were conducted with a spray chamber where representative S. albicosta populations were exposed to labeled rates of a commercial bifenthrin formulation. Experiments resulted in 100% mortality for all populations, instars, insecticide rates, and carrier volumes, suggesting that levels of resistance estimated for bifenthrin active ingredient did not seem to impact the efficacy of the correspondent commercial product under controlled conditions. Results obtained from this research indicate that control failures reported in Nebraska could be associated with factors other than insecticide resistance, such as issues with the application technique, environmental conditions during and/or after application, or the insect's natural behavior. Data generated will assist future S. albicosta resistance management programs.