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Frogeye leaf spot (FLS) is a foliar disease of soybean (Glycine max) caused by Cercospora sojina. Application of fungicide products that contain quinone outside inhibitor (QoI) active ingredients has been one of the major tools used in the management of this disease, but, since 2010, QoI-resistant C. sojina isolates have been confirmed in over 20 states in the United States, including Indiana. In summer 2019 and 2020, 406 isolates of C. sojina were collected from 32 counties across Indiana and screened for QoI resistance using a PCR-restriction fragment length polymorphism (RFLP) method. An in vitro fungicide sensitivity test was also performed on a subset of isolates to evaluate their sensitivity to three QoI fungicides: azoxystrobin, pyraclostrobin, and picoxystrobin. A discriminatory dose of picoxystrobin was established as 1 µg/ml by testing five concentrations (0.001, 0.01, 0.1, 1, and 10 µg/ml). QoI-resistant isolates were found in 29 counties, and 251 of the 406 isolates (61.8%) were confirmed to be resistant to QoI fungicides based on PCR-RFLP results. Partial nucleotide sequences of the cytochrome b gene from four resistant and four sensitive isolates corroborated the presence and absence, respectively, of the G143A mutation. Results from the sensitivity assays with discriminatory doses of azoxystrobin (1 µg/ml) and pyraclostrobin (0.1 µg/ml) also supported the findings from the PCR-RFLP assay, because all QoI-resistant isolates were inhibited less than 50% relative to a no-fungicide control when exposed to these doses. Resistant isolates harboring the G143A mutation also exhibited resistance to picoxystrobin. The effective concentrations to inhibit mycelial growth by 50% relative to the nonamended control (EC50) in QoI-sensitive isolates ranged from 0.087 to 0.243 µg/ml, with an overall mean of 0.152 µg/ml, while EC50 values in QoI-resistant isolates were established as >10 µg/ml for picoxystrobin. Results from this study indicated that QoI-resistant C. sojina isolates are spread throughout Indiana and exhibit cross-resistance to QoI fungicides.

Field experiments were conducted in Illinois, Indiana, Iowa, Michigan, Wisconsin and Ontario Canada in 2019 and 2020 to evaluate the integrated effects of host resistance, seed treatment, and seeding rates on root rot (RR) and foliar symptoms of sudden death syndrome (FDX) and soybean yield. Seed treatments included a nontreated control and fluopyram in 2019. In 2020, commercial base treatment, base + fluopyram, and base + pydiflumetofen were tested. Base treatment included metalaxyl + pyraclostrobin + fluxapyroxad + clothianidin. Seed treatments were tested on susceptible and moderately resistant (MR) cultivars, which were planted at 272,277, 346,535 and 420,792 seeds/ha. Seed treatment with fluopyram or pydiflumetofen both reduced FDX and protected yield. Fluopyram reduced RR by about 10%, but RR was not different between pydiflumetofen and the base treatment in 2020. Both seed treatments reduced FDX, but reduction was greater for fluopyram (43.2%) than for pydiflumetofen (24.3%) based on 2020 results. Seeding rate had no effect on foliar symptoms, but the highest seeding rate showed increased RR in 2019, and greater yield both years. Performance of MR cultivars was inconsistent across both years. In 2019, MR cultivars reduced RR by 8.9%, however, in 2020, MR cultivar had more RR than the susceptible cultivar. Also, FDX was only reduced by the MR cultivar in 2020. Integrating seed treatment, host resistance, and adequate seeding rates helped maximize yield in fields with SDS.

Tar spot, caused by Phyllachora maydis, is the most significant disease of corn in the north central United States. Elucidating an integrated management approach to protect grain yield is a high priority. The integration of tillage, hybrid, and fungicide application on tar spot severity, canopy greenness, and grain yield was assessed in Indiana in 2019, 2020, and 2021. A split-plot arrangement of two tillage treatments as main plots with factorial arrangement of subplots with three hybrids (tar spot susceptible and two partially resistant) and fungicide application (propiconazole +benzovindiflupyr +azoxystrobin) were evaluated. Further, a multistate study comparing two hybrids (susceptible and partially resistant) and fungicide application (propiconazole +benzovindiflupyr +azoxystrobin) was conducted in Indiana, Michigan, and Wisconsin in 2020. This research demonstrates that partially resistant hybrids with a sAUDPC of 2.5 and 3.0 had significantly less tar spot than a susceptible hybrid with a sAUDPC of 10.1 and increased canopy greenness rating of 48.1 and 51.5% which were significantly higher than the susceptible hybrid at 13.0% at maturity. Tar spot severity was further reduced and canopy greenness increased with a fungicide application in the susceptible hybrid. These results suggest that partial resistance alone may be used to manage tar spot. Yields did not differ significantly across hybrids with or without a fungicide application. However, a general trend of preserved yield potential was observed in the treatments with fungicide, indicating that knowledge of genetics and yield potential will be necessary to achieve the most benefit from partially resistant hybrids and judicious fungicide applications.

Tar spot of corn caused by Phyllachora maydis has recently led to significant yield losses in the eastern corn belt of the Midwestern United States. Foliar fungicides containing quinone outside inhibitors (QoI), demethylation inhibitors (DMI), and succinate dehydrogenase inhibitors (SDHI) are commonly used to manage foliar diseases in corn. To mitigate the losses from tar spot, 13 foliar fungicides containing single or multiple modes of action (MOA/Fungicide Resistance Action Committee groups) were applied at their recommended rates in a single application at the standard VT/R1 (tassel/silk) growth stage timing to evaluate their efficacy against tar spot in a total of eight field trials in Illinois, Indiana, Michigan, and Wisconsin during 2019 and 2020. The single MOA fungicides included either a QoI or DMI. The dual MOA fungicides included a DMI with either a QoI or SDHI, and fungicides containing three MOAs included a QoI, DMI, and SDHI. Tar spot severity estimated as the percentage of leaf area covered by P. maydis stroma on the ear leaf of the nontreated control at dent growth stage ranged from 1.6 to 23.3% in the trials. Averaged across eight field trials all foliar fungicide treatments significantly reduced tar spot severity, but only Delaro 325SE (prothioconazole + trifloxystrobin), Revytek 3.33LC (mefentrifluconazole + pyraclostrobin + fluxapyroxad), and Veltyma 3.34S (mefentrifluconazole + pyraclostrobin) significantly increased yield over the nontreated control. When comparing groups of fungicide treatments by the number of MOAs, foliar fungicide products that had two or three MOAs decreased tar spot severity over not treating and products with one MOA. In addition, the fungicide group that contained all three MOAs significantly increased yield over not treating with a fungicide or using a single MOA group.

In September 2021, signs of black circular to oval shaped fungal structures (stromata) were observed on corn (Zea mays L.) leaves on a non-commercial inbred line in Todd County, Kentucky. Signs were only observed in a small pocket within the larger field, with disease levels ranging from 1- 5% incidence and 1-25% severity on individual leaves affected in the field. Corn leaves had senesced and only fungal structures were available to aid in diagnosis. Microscopic examination of stromata uncovered ascomata within the clypei/stromata. Further examination of ascomata revealed multiple asci containing eight hyaline, uniseriate, aseptate, oval to ovoid ascospores ranging in size from 8 to 12 µm x 5 to 7 µm. Observed signs were consistent with published reports of tar spot caused by Phyllachora maydis (Parbery 1967; Valle-Torres et al. 2020). For molecular confirmation of the causal agent, corn leaves were surface sterilized in diluted bleach (10%) for 30 seconds and stromata were excised from the leaves using a sterile scalpel. Five to seven stromata were placed into each microcentrifuge tube. Liquid nitrogen was added to the microcentrifuge tubes and the frozen stromata were ground using a sterilized pestle. The ground stromata tissue was used for DNA extraction using a Synergy 2.0 plant DNA extraction kit (OPS Diagnostics, Lebanon, NJ). A portion of the internal transcribed spacer (ITS) region was amplified by PCR utilizing ITS-4 and ITS-5 primers. Amplicons were subjected to Sanger sequencing to obtain a consensus sequence. Using the BLASTn algorithm the consensus sequence shared 100% similarity to three P. maydis Genbank accessions: MG881848.1, MG8814847.1, MG881846.1. A representative sequence was deposited in GenBank (accession no. OQ034699.1). Due to P. maydis being an obligate parasite, Koch’s postulates were not attempted.

Soybean production in the Upper Midwest region of the United States is consistently limited by the disease Sclerotinia stem rot (SSR). To control SSR, multiple management practices have been studied and implemented to reduce SSR development and preserve yield. This study examined the effects of integrating soybean seeding rates and pesticide programs under nitrogen fertilizer applications in the form of urea (46-0-0) that may occur due to management for other crops, such as corn. From ten site-years between 2020 and 2021, low seeding rates decreased SSR development while also decreasing yields and partial profits. The effect of pesticide applications on SSR development was influenced by both seeding rates and nitrogen applications. Consistently, applications of the fungicide, Endura, reduced SSR to the lowest levels, while also maintaining the highest yields and partial profits. Soybeans grown with nitrogen applications experienced increased SSR development, and decreased yields and partial profits. Overall, this work suggests that using low seeding rates and fungicides improves the management of SSR, and using nitrogen fertilizer applications can result in greater SSR development and decreased economic returns, especially in fields with a history of SSR.

Frogeye leaf spot (FLS) is a foliar disease of soybean (

A 2021 epidemic of tar spot of corn caused by Phyllachora maydis led to significant yield losses in the midwestern United States and Ontario, Canada. Uniform fungicides trials consisting of nine foliar fungicides applied at the tassel (VT) or silk (R1) growth stage were evaluated for tar spot management in five field trials in the midwestern United States and Ontario, Canada, in 2021. All nine foliar fungicide treatments significantly reduced tar spot severity, but only Delaro Complete (prothioconazole + fluopyram + trifloxystrobin), Revytek (mefentrifluconazole + pyraclostrobin + fluxapyroxad), and Veltyma (mefentrifluconazole + pyraclostrobin) protected yield compared with the nontreated control.

Objective: Tar spot is a foliar disease of corn caused by Phyllachora maydis, which produces signs in the form of stromata that bear conidia and ascospores. Phyllachora maydis cannot be cultured in media; therefore, the inoculum source for studying tar spot comprises leaves with stromata collected from naturally infected plants. Currently, there is no effective protocol to induce infection under controlled conditions. In this study, an inoculation method was assessed under greenhouse and growth chamber conditions to test whether stromata of P. maydis could be induced on corn leaves. Results: Experiments resulted in incubation periods ranging between 18 to 20 days and stromata development at the beginning of corn growth stage VT-R1 (silk). The induced stromata of P. maydis were confirmed by microscopy, PCR, or both. From thirteen experiments conducted, four (31%) resulted in the successful production of stromata. Statistical analyses indicate that if an experiment is conducted, there are equal chances of obtaining successful or unsuccessful infections. The information from this study will be valuable for developing more reliable P. maydis inoculation methods in the future.

Tar spot is a major foliar disease of corn caused by the obligate fungal pathogen Phyllachora maydis, first identified in Indiana in 2015. Under conducive weather conditions, P. maydis causes significant yield losses in the United States and other countries, constituting a major threat to corn production. Relatively little is known about resistance to tar spot other than a major quantitative gene that was identified in tropical maize lines. To test for additional sources of resistance against populations of P. maydis in North America, 26 parental inbred lines of the nested associated mapping (NAM) population were evaluated for tar spot resistance in Indiana in replicated field trials under natural infection for 3 years. Tar spot disease severity was scored visually using a 0-to-100% scale. Maximum disease severity (MDS) for tar spot scoring at reproductive growth stage ranged from 0 to 48.3%, with 0% being most resistant and 48.3% being most susceptible. Nine inbred lines were resistant to P. maydis with MDS ranging from 0 to 5.0%, six were moderately resistant (5.2 to 10.6% MDS), two were moderately susceptible (11.7 to 26.0% MDS), and the remaining eight inbred lines were rated as susceptible (30.0 to 48.3% MDS). There was some variability between years, due to higher disease pressure after 2019. Inbred B73, the common parent of the NAM populations, was rated as susceptible, with MDS of 30.0%. The nine highly resistant lines provide a potential source of new genes for genetic analysis and mapping of tar spot resistance in corn.

Tar spot is a foliar disease of corn threatening production across the Americas. The disease was first documented in Mexico in 1904 and is now present in 15 additional countries throughout Central America, South America, and the Caribbean. Researchers and growers in Central America, South America, and the Caribbean consider tar spot to be a disease complex caused by multiple fungal pathogens. When environmental conditions are conducive for infection, these regions have experienced yield losses that can reach up to 100%. In 2015, tar spot was detected in the United States for the first time in Illinois and Indiana. Since that time tar spot has spread across the U.S. corn-growing region, and the disease has been found in Florida, Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, Pennsylvania, and Wisconsin. In 2020, tar spot was also found in southwest Ontario, Canada. Losses in the United States due to tar spot totaled an estimated 241 million bushels from 2018 to 2020. With the potential to continue to spread across the U.S. corn-growing states, much greater losses could result when environmental conditions are conducive.

Soybean (Glycine max [L.] Merrill) yield losses as a result of plant diseases were estimated by university and government plant pathologists in 29 soybean producing states in the United States and in Ontario, Canada, from 2015 through 2019. In general, the estimated losses that resulted from each of 28 plant diseases or pathogens varied by state or province as well as year. Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) caused more than twice as much loss as any other disease during the survey period. Seedling diseases (caused by various pathogens), Sclerotinia stem rot (white mold) (caused by Sclerotinia sclerotiorum [Lib.] de Bary), and sudden death syndrome (caused by Fusarium virguliforme O’Donnell & T. Aoki) caused the next greatest yield losses, in descending order. Following SCN, the most damaging diseases in the northern United States and Ontario differed from those in the southern United States. The estimated mean economic loss from all soybean diseases, averaged across the United States and Ontario, Canada was US$45 per acre (US$111 per hectare). The outcome from the current survey will provide pertinent information regarding the important soybean diseases and their overall severity in the soybean crop and help guide future research and Extension efforts on managing soybean diseases.

Phyllachora maydis is an important fungal pathogen that causes tar spot of corn and has led to significant yield loss in the United States and other countries. P. maydis is an obligate biotroph belonging to the Sordariomycetes class of Ascomycota. Due to the challenges posed by their obligate nature, there is no genome sequence available in the Phyllachora genus. P. maydis isolate PM01 was collected from a corn field in Indiana and the genome was determined by next-generation sequencing. The assembly size is 45.7 Mb, with 56.46% repetitive sequences. There are 5,992 protein-coding genes and 59 are predicted as effector proteins. This genome resource will increase our understanding of genomic features of P. maydis and will assist in studying the corn–P. maydis interaction and identifying potential resistant candidates for corn breeding programs.

Gray leaf spot (Cercospora zeae-maydis) is a foliar disease of corn (Zea mays) that consistently reduces yields across the United States and is an annual concern in Indiana corn production. Field trials were conducted in West Lafayette, IN, over 3 years (2016 to 2018) to evaluate the effectiveness of 12-leaf collar stage (V12) foliar fungicide applications compared with tasseling (VT) applications for gray leaf spot management and yield. Results indicated that during years in which foliar disease severity was less than 4%, there was no effect of application timing on gray leaf spot severity. In 2018, when gray leaf spot levels exceeded 5%, significantly less disease was observed in treatments receiving VT applications compared with V12 applications. Application timing did not affect yield in any year of the experiment. In 2016, benzovindiflupyr + azoxystrobin + propiconazole resulted in greater yields compared with the nontreated control, and in 2018, pyraclostrobin + metconazole and benzovindiflupyr + azoxystrobin + propiconazole resulted in greater yields compared with the nontreated control. This research indicates that in high disease pressure environments and years, Indiana farmers may want to continue to apply fungicides at VT rather than apply prior to tassel.

Annual reductions in corn (Zea mays L.) yield caused by diseases were estimated by university Extension-affiliated plant pathologists in 26 corn-producing states in the United States and in Ontario, Canada, from 2016 through 2019. Estimated loss from each disease varied greatly by state or province and year. Gray leaf spot (caused by Cercospora zeae-maydis Tehon & E.Y. Daniels) caused the greatest estimated yield loss in parts of the northern United States and Ontario in all years except 2019, and Fusarium stalk rot (caused by Fusarium spp.) also greatly reduced yield. Tar spot (caused by Phyllachora maydis Maubl.), a relatively new disease in the United States, was estimated to cause substantial yield loss in 2018 and 2019 in several northern states. Gray leaf spot and southern rust (caused by Puccinia polysora Underw.) caused the most estimated yield losses in the southern United States. Unfavorable wet and delayed harvest conditions in 2018 resulted in an estimated 2.5 billion bushels (63.5 million metric tons) of grain contaminated with mycotoxins. The estimated mean economic loss due to reduced yield caused by corn diseases in the United States and Ontario from 2016 to 2019 was US$55.90 per acre (US$138.13 per hectare). Results from this survey provide scientists, corn breeders, government agencies, and educators with data to help inform and prioritize research, policy, and educational efforts in corn pathology and disease management.

Tar spot of corn, caused by Phyllachora maydis, has been reported in several upper Midwest states in the United States. This has led to expanded efforts to more thoroughly understand the biology of P. maydis and the epidemiology of tar spot. This study determined the potential for P. maydis ascospore release and germination from overwintered P. maydis-infected corn residues from various locations in the upper Midwest. Corn residue samples collected in the spring of 2019 from 12 fields in four states were examined. Ascospore release and germination were observed in all residue samples collected. The mean total number of ascospores released per milliliter of water ranged from 3.6 × 103 to 4.8 × 106 after 4-h incubation and 3.7 × 103 to 4.4 × 106 after 24-h incubation. The mean percent spore germination ranged from 0.7 to 24.1% after 4-h incubation and 2.4 to 24.9% after 24-h incubation. There was a significant inverse relationship between total numbers of ascospores released and the percent germination of the ascospores. Samples from Illinois consistently yielded the greatest total ascospore release but were also consistently among the samples with the lowest percent ascospore germination. Samples from Wisconsin and Indiana were among the lowest for total ascospore numbers but were among the highest for total ascospore germination. These findings provide evidence that P. maydis can overwinter in multiple areas of the upper Midwest. Future research should focus on reducing infested corn residue to reduce initial infection by P. maydis.

Tar spot is a foliar disease of corn characterized by fungal fruiting bodies that resemble tar spots. The disease emerged in the U.S. in 2015, and severe outbreaks in 2018 caused an economic impact on corn yields throughout the Midwest. Adequate epidemiological surveillance and disease quantification are necessary to develop immediate and long-term management strategies. This study presents a measurement framework that evaluates the disease severity of tar spot using unmanned aircraft systems (UAS)-based plant phenotyping and regression techniques. UAS-based plant phenotypic information, such as canopy cover, canopy volume, and vegetation indices, were used as explanatory variables. Visual estimations of disease severity were performed by expert plant pathologists per experiment plot basis and used as response variables. Three regression methods, namely ordinary least squares (OLS), support vector regression (SVR), and multilayer perceptron (MLP), were used to determine an optimal regression method for UAS-based tar spot measurement. The cross-validation results showed that the regression model based on MLP provides the highest accuracy of disease measurements. By training and testing the model with spatially separated datasets, the proposed regression model achieved a Lin’s concordance correlation coefficient (ρc) of 0.82 and a root mean square error (RMSE) of 6.42. This study demonstrated that we could use the proposed UAS-based method for the disease quantification of tar spot, which shows a gradual spectral response as the disease develops.

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.

Tar spot is a foliar disease of corn characterized by raised black spots that may or may not be surrounded by a tan or brown halo called a fisheye. Severe infection can lead to a 10-50% yield loss in corn. Timely detection of early symptoms is essential for implementing management tactics to reduce the disease. This study aims to propose a machine learning pipeline to estimate disease severity of tar spot of corn using unmanned aircraft systems (UAS) data. The overall process comprises structure from motion (SfM), canopy attributes extraction, dimensionality reduction, and regression. The proposed method was applied to UAS data collected from research subplots located at Pinney Purdue Agricultural Center (PPAC), Indiana, USA. The study contributes to the expansion of UAS technology in agriculture by providing reliable disease severity information of tar spot of corn.

Tar spot of corn has been a major foliar disease in several Latin American countries since 1904. In 2015, tar spot was first documented in the United States and has led to significant yield losses of approximately 4.5 million t. Tar spot is caused by an obligate pathogen, Phyllachora maydis, and thus requires a living host to grow and reproduce. Due to its obligate nature, biological and epidemiological studies are limited and impact of disease in corn production has been understudied. Here we present the current literature and gaps in knowledge of tar spot of corn in the Americas, its etiology, distribution, impact and known management strategies as a resource for understanding the pathosystem. This will in turn guide current and future research and aid in the development of effective management strategies for this disease.

Tar spot on corn, caused by the fungus (Phyllachora maydis Maubl. [Phyllachorales: Phyllachoraceae]), is an emerging disease in the United States. In 2018 and 2019, significant but localized epidemics of tar spot occurred across the major corn producing region of the Midwest. After being first detected in 2015, tar spot was detected in 135 and 139 counties where the disease was not previously detected in 2018 and 2019, respectively, and is now established across 310 counties across the United Sates. Foliage with signs (stromata) of P. maydis and symptoms of tar spot were collected from 128 fields in 2018 and 191 fields in 2019, across seven states. Samples were assessed for severity of fungal stromata (percent leaf area covered with stromata) on foliage and the incidence of fisheye lesions (proportion of lesions with fisheye symptoms) associated with fungal stromata. Stromatal severity on samples in 2018 ranged from 0.5 to 67% and incidence of fisheye lesions ranged from 0 to 12%, whereas in 2019, stromatal severity ranged from 0.1 to 35% and incidence of fisheye lesions ranged from 0 to 80%, with 95% of samples presenting less than 6% incidence of fisheye lesions. Tar spot has spread substantially from where it was first reported in the United States. Collaborative efforts to monitor the spread and educate clientele on management are essential as this disease spreads into new areas.