Foliar Fungicides Research Articles

Double‐crop soybean management practices for high yield and profitability

AbstractDouble‐crop soybean [Glycine max (L.) Merr.] production in Kentucky involves planting soybean after soft red winter wheat (Triticum aestivum L.) harvest during June and July. Double‐crop soybean yields are lower than full‐season soybean yield planted earlier in the spring. This research aimed to determine the effect of seeding rate, seed treatment, and applying foliar fungicide and insecticide at the R3 growth stage at two planting timings on double‐crop soybean seed yield, yield components, and seed quality. Field trials were established in Princeton, KY, in 2017, 2018, and 2019 after wheat harvest. Planting double‐crop soybean early, after wheat was harvested at 20 to 22% grain moisture, resulted in increased seed yield, seeds ft–2, and protein concentration compared with double‐crop soybean planted later. A seeding rate of 225,000 seeds acre–1 resulted in increased seed yield, seeds ft–2, and seed protein concentration compared with 150,000 seeds acre–1. A seed treatment including fungicides and an insecticide did not impact seed yield, yield components, or seed protein or oil concentration compared with no seed treatment. Applying a prophylactic foliar fungicide and insecticide treatment at the R3 growth stage increased seed yield and seed mass compared with an economic threshold application. In addition, the most intensive management (225,000 seeds acre–1, seed treatment, and prophylactic fungicide and insecticide) yielded ∼25% more than the base treatment and had more seeds ft–2. The results are the first to indicate the potential for intensive management practices to increase double‐crop soybean productivity in Kentucky.

Effects of Mowing, Seeding Rate, and Foliar Fungicide on Soybean Sclerotinia Stem Rot and Yield

Sclerotinia stem rot (SSR or white mold), caused by Sclerotinia sclerotiorum (Lib.) DeBary, is an economically important fungal disease of soybean. SSR routinely causes yield loss in the upper Corn Belt of the United States due to wet, humid conditions that coincide with moderate temperatures. This study investigated the novel cultural practice of mechanical cutting, or mowing, as an SSR management practice across multiple seeding rates. Mowing soybean during early vegetative growth alters plant architecture and growth habit. This results in a microclimate within the canopy less suitable for disease development. Field trials were conducted in Iowa, Illinois, Michigan, and Wisconsin in 2017 and 2018. Experimental design was a randomized complete block with four replications. Treatments included mowing (mowing and no mowing), seeding rate (197,684, 271,816, and 345,947 seeds/ha), and fungicide application (boscalid, Endura, and no fungicide). Soybean was mowed at approximately the V4 (four unfolded trifoliate leaves) growth stage. Mowing reduced disease in multiple locations; however, it also reduced yield in most of the locations. In general, there was less SSR in plots with lower seeding rates. Fungicide significantly reduced SSR in two of the five site-years for which disease was observed. Significant yield response to fungicide was also observed in two of the nine total field trials. Results indicate cultural practices such as mowing and reduced seeding rate can decrease SSR severity but also can impact potential yield. Additionally, yield response to SSR management practices may not be observed if disease is absent or at low levels.

Impact of Foliar Fungicides on Disease and Silage Quality of Brown Midrib Corn Hybrids in Wisconsin

Corn (Zea mays L.) is one of the most widely grown crops in the United States due to its importance as a feed, food, and fuel crop. Silage is a high-energy, fermented feed that uses the entire corn plant and is important for feeding dairy cows. Any disease that affects the plant’s physiology can reduce silage quality. The goal of this study was to evaluate fungicide treatments on silage corn hybrids to determine their effect on fungal diseases, including those caused by Fusarium graminearum, on silage quality. Foliar fungicide trials were conducted in Arlington, Wisconsin, in 2018 and 2019 and included two brown-midrib silage hybrids. In-field disease ratings were collected for foliar disease symptoms, ear rot severity, and lodging. Harvested silage was analyzed for yield, quality parameters, and mycotoxin (deoxynivalenol, DON) concentration. There were significant differences in all measured parameters between years and hybrids; however, only the foliar disease ratings were consistently reduced by the use of fungicide treatments. DON concentrations were significantly lower for two fungicide treatments in one hybrid in 2019. There were no significant differences among the treatments used on yield or any quality parameters in this study. More research needs to be done to find potential fungicides that can consistently reduce F. graminearum damage and DON concentration in silage corn.

Fungicide, insecticide, and foliar fertilizer effect on soybean yield, seed composition, and canopy retention

AbstractSoybean [Glycine max (L.) Merr.] yield has increased over time through the introduction of new varieties and improved agronomic practices. However, seed protein concentration has decreased. We conducted field studies in 2018 and 2019 to investigate the effects of fungicide, insecticide, and foliar fertilizer application on grain yield and seed quality in two soybean maturity groups (MG). In‐season treatments targeted nutrient availability and soybean canopy duration during the seed‐filling period by fungicide, insecticide, or foliar fertilizer application at the onset of this period. Biomass samples were collected at R5, R6, and R7 and partitioned into plant parts. Year, location, and MG often influenced yield and seed composition, but foliar fungicide, insecticide, or fertilizer application had no impact on these parameters.

Winter Wheat Response to Different Fungicide Management (Products and Timing of Application) During the 2019-2020 Growing Season

Foliar fungicides can improve wheat grain yield in Kansas, but there is limited information on the efficacy of different products as well as the timing of application. We conducted a field study in five Kansas locations to evaluate the yield, test weight, and protein responses of WB-Grainfield to different commercial fungicides applied at different times during the growing season. The trial was conducted in a randomized complete block design to evaluate (1) a non-treated control; Topguard applied at 5 ounces per acre at (2) jointing, (3) heading, and (4) jointing plus heading; (5) Delaro applied at 6 oz/a at jointing; (6) Absolute Maxx applied at 5 ounces per acre at heading; (7) Delaro at jointing plus Absolute Maxx at heading at the rates previously specified; and (8) Nexicor applied at 13 oz/a at heading. The study was conducted near Conway Springs, Great Bend, two sites near Hutchinson (optimum- and late-sowing date), and Leoti. Grain yield across locations ranged from 36 to 72.9 bushels per acre. A significant fungicide by location interaction on grain yield resulted from two locations showing no response to fungicide; two locations resulting in the highest yield when fungicide at heading was presented in the evaluated treatment; and one location showing all fungicide treatments outyielding the control. Similar results were obtained for test weight, where fungicides at heading seemed to benefit test weight at all locations except at the driest one. There were no consistent effects of foliar fungicide management on wheat grain protein concentration. This research is an initial step in determining the benefits of foliar fungicide to winter wheat yield and to date, a preliminary conclusion highlights the usefulness of a heading fungicide application when precipitation is not a limiting factor to yields, without consistent differences among the evaluated products.

Reaction of winter wheat and barley cultivars to Fusarium pseudograminearum‐inoculated fields in the dryland Pacific Northwest, USA

AbstractFusarium crown rot (FCR) of winter wheat (Triticum aestivum L.), caused by Fusarium pseudograminearm and Fusarium culmorum, is a yield‐limiting disease in arid wheat‐producing areas of the inland Pacific Northwest. Foliar fungicide applications and currently available seed treatments do not control FCR. Alternative crops that provide a rotational benefit to reduce disease are not economically feasible. Major‐gene resistance is unavailable, but there is preliminary evidence that some wheat and barley (Hordeum vulgare L.) cultivars are more resistant than others. We followed up on preliminary work by growing 14 varieties of winter wheat, planted with in‐furrow FCR inoculum, in 2018 and 2019 in Morrow County, Oregon—one of the world's driest wheat producing regions. Two barley cultivars were added to the experiment during the second year of research. Evaluations of cultivar resistance were made by conducting aboveground visual assessments by counting whiteheads, prematurely senesced wheat heads that are indicative of FCR infection. Whitehead count information was correlated with yield and grain volume weight data. Maximum whitehead counts were measured in plots of the FCR‐susceptible check cultivar ‘Stephens’. There was no evidence of a cultivar‐specific relationship between whitehead count and corresponding values for yield and grain volume weight. There was limited evidence that some cultivars have the capacity to compensate for effects of disease.

High-Throughput Metabarcoding Characterizes Fungal Endophyte Diversity in the Phyllosphere of a Barley Crop

Over the last decade, the microbiome has received increasing attention as a key factor in macroorganism fitness. Sustainable pest management requires an understanding of the complex microbial endophyte communities existing symbiotically within plants and the way synthetic pesticides interact with them. Fungal endophytes are known to benefit plant growth and fitness and may deter pests and diseases. Recent advances in high-throughput sequencing (HTS) have enabled integrative microbiome studies, especially in agricultural contexts. Here, we profile the fungal endophyte community in the phyllosphere of two barley (Hordeum vulgare) cultivars exposed to two systemic foliar fungicides using metabarcoding, an HTS tool that constructs community profiles from environmental DNA. We studied the fungal nuclear ribosomal large subunit D2 and internal transcribed spacer 2 (ITS2) DNA markers through a bioinformatics pipeline introduced here. We found 88 and 128 unique amplicon sequence variants (ASVs) using the D2 and ITS2 metabarcoding assays, respectively. With principal coordinate analysis and permutational analysis of variance, ASV diversity did not change in response to barley cultivar or fungicide treatment; however, the community structure of unsprayed plants did change between two collection times 8 days apart. The workflow described here can be applied to other microbiome studies in agriculture and we hope it encourages further research into crop microbiomes to improve agroecosystem management.

Estimating Soybean Radiation Use Efficiency Using a UAV in Iowa

Radiation use efficiency (RUE) is difficult to estimate and unreasonable to perform on a small plot scale using traditional techniques. However, the increased availability of Unmanned Aerial Vehicles (UAVs) provides the ability to collect spatial and temporal data at high resolution and frequency, which has made a potential workaround. An experiment was completed in Iowa to (i) demonstrate RUE estimation of soybean [Glycine max (L.) Merr.] from reflectance data derived from consumer-grade UAV imagery and (ii) investigate the impact of foliar fungicides on RUE in Iowa. Some fungicides are promoted to have plant health benefits beyond disease protection, and changes in RUE may capture their effect. Frogeye leaf spot severity did not exceed 2%. RUE values ranged from 0.98 to 1.07 and 0.96 to 1.12 across the entire season and the period post-fungicide application, respectively, and fell within the range of previously published soybean RUE values. Plots treated with fluxapyroxad + pyraclostrobin had more canopy cover (p = 0.078) compared to the non-treated control 133 days after planting (DAP), but yields did not differ. A “greening effect” was detected at the end of the sample collection. RUE estimation using UAV imagery can be considered a viable option for the evaluation of management techniques on a small plot scale. Since it is directly related to yield, RUE could be an appropriate parameter to elucidate the impact of plant diseases and other stresses on yield.

Corn-soybean rotation, tillage, and foliar fungicides: Impacts on yield and soil fungi

• Rotating crops is key to achieving high soybean and corn yield. • Prophylactic foliar fungicides resulted in a small increase in soybean seed yield. • Continuous corn and soybean have distinct bulk soil fungal communities. • Foliar fungicide treatments did not have an impact on bulk soil fungal communities. Fungal diseases can have a detrimental impact on soybean and corn yield. Foliar fungicides are used to manage fungal diseases and minimize yield loss, along with cultural practices like tillage and crop rotation. Prophylactic foliar fungicide use does not consistently increase yield for corn and soybean, especially when disease pressures are low. Also, there are concerns about the impact of fungicides on non-target organisms, including fungi living in the soil. We tested the effects of tillage, crop rotation, and foliar fungicide use on corn grain and soybean seed yield over three growing seasons. For both crops, rotation was key to achieving high yields, although there was an interaction of tillage × crop rotation for soybean and crop rotation × fungicide for corn. For soybean seed yield, both foliar fungicide treatments showed a small yield increase over untreated plots. Additionally, we assessed bulk soil fungal communities in a subset of treatments (crop rotation and fungicide treatments in no-till plots), using ITS sequencing and PLFA-FAME. We observed distinct fungal communities in the continuously cropped treatments, while annually rotated communities were very similar. There was also greater overall microbial biomass and a higher relative abundance of arbuscular mycorrhizae fungi associated with continuous corn. There were no differences in soil fungal communities or microbial biomass associated with foliar fungicide treatments. Based on our findings, we recommend that farmers use integrated pest management strategies to manage fungal diseases, which may include fungicide applications, if they are justified by economic disease thresholds or prediction tools.

Meta-Analysis of Soybean Yield Response to Foliar Fungicides Evaluated from 2005 to 2018 in the United States and Canada

Random-effect meta-analyses were performed on data from 240 field trials conducted between 2005 and 2018 across nine U.S. states and Ontario, Canada, to quantify the yield response of soybean after application of foliar fungicides at beginning pod (R3) stage. Meta-analysis showed that the overall mean yield response when fungicide was used compared with not applying a fungicide was 2.7% (110 kg/ha). Moderator variables were also investigated and included fungicide group, growing season, planting date, and base yield, which all significantly influenced the yield response. There was also evidence that precipitation from the time of planting to the R3 growth stage influenced yield when fungicide was used (P = 0.059). Fungicides containing a premix of active ingredients from multiple groups (either two or three ingredients) increased the yield by 3.0% over not applying a fungicide. The highest and lowest yield responses were observed in 2005 and 2007, respectively. Better yield response to fungicides (a 3.0% increase) occurred when soybean crops were planted not later than 21 May and when total precipitation between planting and the R3 application date was above historic averages. Temperatures during the season did not influence the yield response. Yield response to fungicide was higher (a 4.7% increase) in average yield category (no spray control yield 2,878 to 3,758 kg/ha) and then gradually decreased with increasing base yield. Partial economic analyses indicated that use of foliar fungicides is less likely to be profitable when foliar diseases are absent or at low levels.

Chemical characteristics and digestibility of forage maize hybrids associated with foliar fungicide application

The objective of this study was to evaluate the effect of foliar fungicide application on the chemical characteristics and in situ digestibility of forage and silage in forage maize hybrids with different grain textures in two sowing seasons. A randomized complete block design was used with four replications, in a 4 x 2 factorial arrangement, 4 hybrids, with and without foliar fungicide application, in two sowing seasons. The hybrids used were DKB240PRO, AS1572PRO, 32R48YH and AG8690PRO3. Data were tested by analysis of variance; the means were compared by Tukey’s test at 5% probability and two non-orthogonal contrasts were performed. The application of fungicide on forage maize hybrids reduced the content of neutral detergent fiber (NDF), acid detergent fiber (ADF), soft dough stage and in the silage produced. The sowing season in December negatively influenced the chemical parameters of forage maize hybrids, compared to sowing in October. Hybrids with highly vitreous endosperm presented the highest contents of NDF and ADF, soft dough stage and in the silage produced. The application of fungicide (trifloxystrobin + prothioconazole) at the V8 and R1 stages positively influenced in situ digestibility soft dough stage and in the silage produced, depending of the sowing season.

Early fungicide treatment reduces blackleg on canola but yield benefit is realized only on susceptible cultivars under high disease pressure

Blackleg [Leptosphaeria maculans (Desm.) Ces. & de Not.] is the most widespread disease of canola (Brassica napus L.) on the Canadian prairies. It has a noticeably increased incidence in recent years possibly due to shifts in the pathogen population and erosion in cultivar resistance. This study was conducted to assess foliar-applied fungicides for mitigating the risk of blackleg. Field trials were conducted at five locations in the Black or Dark-Brown Soil Zones for four years using the susceptible canola ‘Westar’. The fungicides pyraclostrobin (Headline®), azoxystrobin (Quadris®), propiconazole (Tilt®), and azoxystrobin + propiconazole (Quilt®) were applied at the 2–4 leaf stage against early infection. For comparisons, pyraclostrobin was also applied at bolting of ‘Westar’ and at the 2–4 leaf stage of two resistant cultivars (‘43E01’, ‘45H29’). These early treatments, except propiconazole, significantly reduced the mean disease incidence (MDI) and disease severity index (DSI) on ‘Westar’, relative to untreated control, reducing the impact of disease on yield by 16.5–26.9%. Late application of pyraclostrobin at bolting was ineffective. Two-application treatments, with pyraclostrobin at the 2–4 leaf stage and propiconazole at the bolting stage, or vice versa, provided no further efficacy or yield benefit relative to the early application of pyraclostrobin alone. None of the treatments showed substantial disease reduction or yield benefit in two low-disease station years (MDI <30%). On the resistant cultivars, pyraclostrobin reduced MDI and DSI, but showed no yield benefit. As resistant canola cultivars are used commonly on the prairies, a routine application of foliar fungicide is not recommended.

Evaluation of pyraclostrobin as a component in seed and foliar fungicides for the management of blackleg (Leptosphaeria maculans) of canola (Brassica napus)

Infection by Leptosphaeria maculans (Desm.) Ces. &amp; de Not., the causal agent of blackleg of canola (Brassica napus L.), can result in seedling death, foliar lesions, and the development of stem cankers on adult plants. Strobilurin fungicides such as pyraclostrobin are popular, as they are effective against a broad range of fungal pathogens, have novel target specificity, and translaminar activity within the plant. The seed treatment Prosper FX (carbathiin + trifloxystrobin + metalaxyl) and an experimental formulation BAS 720 F (pyraclostrobin + fluxapyroxad + metalaxyl) were evaluated for their efficacy in managing blackleg when applied alone or in combination with the foliar fungicides Priaxor (pyraclostrobin + fluxapyroxad) or Tilt 250 EC (propiconazole). Experiments were conducted with the blackleg-susceptible cultivar ‘Westar’ and the moderately resistant cultivar ‘Dekalb 73-15 RR’ under greenhouse and field conditions in 2012 and 2013. In one greenhouse trial, all fungicide treatments significantly reduced stem blackleg severity on ‘73-15’ and ‘Westar’ compared with the inoculated–untreated controls. During 3 of 4 site-years, the combination of the experimental seed treatment BAS 720 F and Priaxor significantly reduced stem disease severity relative to the inoculated–untreated control by 60%–77% for ‘73-15’ and by 50%–75% for ‘Westar’. This treatment also resulted in a significant yield increase relative to the inoculated–untreated control in ‘Westar’ in 2 site-years by 24% and 56%. The results of the study suggest a reduction in blackleg symptoms and improved yields when canola is treated with a combination of seed and foliar fungicides, especially when cropping a susceptible cultivar.

Comparison of aerial and ground sprayer fungicide application technologies on canopy coverage, disease severity, lodging, and yield of corn

Fungicides may be applied to corn using an airplane or a ground sprayer. Questions regarding which technology is better at coverage throughout the corn canopy are common among farmers and agronomists. The objectives of this study were to compare the efficacy of three application technologies in terms of canopy coverage, foliar disease management, lodging and yield response. A fungicide was applied to corn at silking (R1) by airplane, a traditional ground sprayer with an overhead spray boom, or a ground sprayer with 360 Undercover sprayers that hang down into the canopy. Replicated on-farm and small-plot trials were conducted across Iowa in 2017 and 2018 for a total of nine site-years. Fungicide coverage was measured as ppm of pyrenetetrasulfonic acid (PTSA) dye detected on corn leaves, percent coverage of water sensitive spray cards, and percent of total application received. Foliar disease data were collected in three zones of the canopy: the upper canopy (UC), the ear leaf (EL), and the lower canopy (LC). Coverage and disease severity were not correlated with yield. In the 2017 on-farm trials, all three application methods delivered similar fungicide coverage on the EL and LC. In 2018, traditional and undercover methods provided greater coverage when compared to aerial application, however, fungicide distribution within the canopy was similar among the application methods. Overall trends indicated the traditional spray method delivered the best coverage to the UC. The aerial spray method delivered the least coverage to the EL and LC for three site-years. The undercover spray method resulted in greater coverage to the LC. Foliar fungicides applied by all three application methods significantly reduced foliar disease severity, and fungicide application methods did not differ from each other, and reduced disease severity to similar levels. Lodging was reduced approximately 50–75% by all application methods. For 8 of 9 site years, fungicide application did not affect yield significantly (P > 0.05), although numerically less yield was consistently recorded in the non-sprayed controls. Our findings indicate these three application technologies were similarly effective in reducing plant disease levels and lodging. But the reduction in disease due to fungicide application did not affect corn yield.

Fungicide efficacy and timing for the management of Stemphylium vesicarium on onion

Stemphylium leaf blight (SLB), caused by Stemphylium vesicarium (Wallr.) E.G. Simmons, has become an important disease of onion (Allium cepa L.) in Ontario, Canada, and the northeastern USA in recent years. The disease presents as elongated lesions on the leaves and severe leaf dieback. The effect on yield is unclear, but the extensive leaf dieback limits uptake of sprout inhibitors that are applied to onion foliage prior to harvest. This can result in high losses in storage. There are no resistant commercial onion cultivars and growers apply foliar fungicides at 7–14-day intervals to manage the disease. Field trials to evaluate fungicide efficacy and disease-forecasting models were conducted at the Muck Crops Research Station, Holland Marsh, Ontario, from 2011 to 2019. Fungicide efficacy declined over the years. The disease-forecasting models reduced the number of fungicide spray applications, but none of the models, including calendar-based applications, reduced SLB severity. Seed treatments containing penflufen, combined with calendar-based fungicide applications, reduced SLB severity. Assessments of fungicide insensitivity in isolates collected locally in 2018 and 2019 demonstrated that 90% of isolates (n = 48) were insensitive to azoxystrobin (a QoI fungicide, FRAC 11) and 57% (n = 47) were insensitive to pyrimethanil (an AP fungicide, FRAC 9). Both fungicides are used extensively on onion in the Holland Marsh but are no longer effective against the population of S. vesicarium that is present in the region. Additional studies on the efficacy of seed treatments, fungicide insensitivity, and potential of biological fungicides are required.

Combining field-level data and remote sensing to understand impact of management practices on producer yields

Abstract Producer field-level data have been used in recent studies to identify suites of management practices that consistently increase yield for a given climate-soil environment. However, the physiological drivers underlying the empirical associations between yield and management practices derived from these studies have remained mostly speculative, particularly in terms of resource capture and conversion into economic yield. We followed an approach consisting of a large producer database, satellite imagery, and crop modeling to assess which key physiological parameters best explain on-farm yield response to producer-chosen management practices across different climate-soil production environments. Survey data on yield and management practices were collected from 5291 soybean fields sown across the US North Central region during 2014-2016. Producer data were grouped into 10 technology extrapolation domains (TEDs) to account for variation in soil, climate, and water regime across producer fields. Simulated phenology and satellite imagery were used to estimate incident (IPAR) and absorbed (APAR) photosynthetically active radiation during the entire crop season and also during the time-span beginning with pod setting and ending with physiological maturity. In each TED, seed yield was increased by early sowing (+13 to +39 kg ha-1d-1), which was physiologically driven by increases in the duration of both crop cycle and critical period, and by a higher APAR. In-season application of foliar fungicide and/or insecticide also resulted in significant yield increase (+0.35 Mg ha−1, p

Modeling the relationship between estimated fungicide use and disease-associated yield losses of soybean in the United States I: Foliar fungicides vs foliar diseases.

Fungicide use in the United States to manage soybean diseases has increased in recent years. The ability of fungicides to reduce disease-associated yield losses varies greatly depending on multiple factors. Nonetheless, historical data are useful to understand the broad sense and long-term trends related to fungicide use practices. In the current study, the relationship between estimated soybean yield losses due to selected foliar diseases and foliar fungicide use was investigated using annual data from 28 soybean growing states over the period of 2005 to 2015. For national and regional (southern and northern United States) scale data, mixed effects modeling was performed considering fungicide use as a fixed and state and year as random factors to generate generalized R2 values for marginal (R2GLMM(m); contains only fixed effects) and conditional (R2GLMM(c); contains fixed and random effects) models. Similar analyses were performed considering soybean production data to see how fungicide use affected production. Analyses at both national and regional scales showed that R2GLMM(m) values were significantly smaller compared to R2GLMM(c) values. The large difference between R2 values for conditional and marginal models indicated that the variation of yield loss as well as production were predominantly explained by the state and year rather than the fungicide use, revealing the general lack of fit between fungicide use and yield loss/production at national and regional scales. Therefore, regression models were fitted across states and years to examine their importance in combination with fungicide use on yield loss or yield. In the majority of cases, the relationship was nonsignificant. However, the relationship between soybean yield and fungicide use was significant and positive for majority of the years in the study. Results suggest that foliar fungicides conferred yield benefits in most of the years in the study. Furthermore, the year-dependent usefulness of foliar fungicides in mitigating soybean yield losses suggested the possible influence of temporally fluctuating abiotic factors on the effectiveness of foliar fungicides and/or target disease occurrence and associated loss magnitudes.

Role of Fungicide Applications on the Integrated Management of Wheat Stripe Rust.

First described in Europe in 1777, stripe rust (SR) caused by Puccinia striiformis Westend. f. sp. tritici Erikss (Pst) is one of the most important and destructive diseases of wheat worldwide. Until 2000, SR was mainly endemic to cooler regions, but since then, new aggressive strains have emerged, spread intercontinentally, and caused severe epidemics in warmer regions across the world. This has put SR as a disease that poses a threat to the world food security. At present, the preferred strategy for control of SR is the access to wheat cultivars with adequate levels of SR resistance. However, wheat breeding programs are not sufficiently advanced to cope with the recently emerged Pst strains. Under this scenario, foliar fungicide applications have become an important component of SR management, but information on the effects of fungicide applications on SR control and wheat cultivar yield response is scarce. This review seeks to provide an overview of the impact and role of fungicides on SR management. With focus on wheat management in the major wheat-growing regions of the world, the review addresses: (a) the efficacy of different fungicide active ingredients, optimal fungicide timing and number of applications in controlling SR, and (b) the impact of fungicide on wheat grain yield response. Inclusion of fungicides in an integrated crop management approach is discussed.

Assessing approaches for stratifying producer fields based on biophysical attributes for regional yield-gap analysis

Large databases containing producer field-level yield and management records can be used to identify causes of yield gaps. A relevant question is how to account for the diverse biophysical background (i.e., climate and soil) across fields and years, which can confound the effect of a given management practice on yield. Here we evaluated two approaches to group producer fields based on biophysical attributes: (i) a technology extrapolation domain spatial framework (‘TEDs’) that delineates regions with similar (long-term average) annual weather and soil water storage capacity and (ii) clusters based on field-specific soil properties and weather during each crop phase in each year. As a case study, we used yield and management data collected from 3462 rainfed fields sown with soybean across the North Central US (NC-US) during four growing seasons (2014–2017). Following the TED approach, fields were grouped into 18 TEDs based on the TED that corresponded to the geographic location of each field. In the cluster approach, fields were grouped into clusters based on similarity of in-season weather and soil. To evaluate how the number of clusters would affect the results, fields were grouped separately into 5, 10, 18, and 30 clusters. The two stratification approaches (TEDs and clusters) were compared on their ability to explain the observed yield variation and yield response to key management factors (sowing date and foliar fungicide and/or insecticide). Lack of stratification of producer fields based on their biophysical background ignored management by environment (M × E) interactions, leading to spurious relationships and results that are not relevant at local level. In the case of the cluster approach, a fine stratification (18 and 30 clusters) explained a larger portion of the yield variance compared with a coarse stratification (5 and 10 clusters). However, for our case study in the NC-US region, we did not find strong evidence that the data-rich clustering approach outperformed the TEDs on the ability to explain yield variation and identify M × E interactions. Only the stratification into 30 clusters exhibited a small improved ability at explaining yield variation compared with the TEDs. However, the use of the clustering approach had important trade-offs, including large amount of data requirements and difficulties to scale results to different regions and over time. The choice of the stratification method should be based on objectives, data availability, and expected variation in yield due to erratic weather across regions and years.

Temporal and spatial dynamics of grapevine anthracnose and its relationship to pathogen survival

AbstractAnthracnose, caused by Elsinoë ampelina, is an economically important grapevine disease in south and southeast Brazil. Control is achieved by lime sulphur application during grapevine dormancy and foliar fungicide sprays until the berries are half‐grown. This study assessed the temporal and spatial progress of grapevine anthracnose under field conditions in order to describe the disease dynamics and its relationship to pathogen survival. The experiment was carried out in a vineyard of table grape Vitis labrusca in Brazil, during the 2014 and 2015 growing seasons. The incidence of vines with diseased leaves, stems and berries and the disease severity on leaves were recorded from bud break to veraison. Monomolecular, logistic and Gompertz models were fitted by non‐linear regression to the incidence and severity data over time to characterize the temporal progress. Ordinary runs, dispersion index, modified Taylor's power law and spatial hierarchy analyses were used to characterize the spatial pattern of diseased plants. The monomolecular model showed the best fit for the incidence progress, with disease progress rates ranging from 0.051 to 0.136 per day. In both seasons, the incidence of diseased plants reached 100% 1 month after bud break. However, the incidence of diseased leaves per plant was around 60% and leaf disease severity was lower than 5% for both years. Ordinary runs and dispersion index analyses revealed that diseased grapevines were distributed randomly on the majority of the assessment dates. Meanwhile, a slight aggregation of diseased vines was observed in the modified Taylor's power law analysis. Our results suggested that the progress of anthracnose incidence and severity over time was governed mainly by the income of the primary inoculum, which survived in the vineyard. Therefore, anthracnose control measures in Brazilian vineyards should be focused on the reduction in inoculum within the vineyard.