Documenting the Establishment, Spread, and Severity of Phyllachora Maydis on Corn, in the United States

Plant Pathology and Microbiology Publications Plant Pathology and Microbiology

2020

Documenting the Establishment, Spread, and Severity of Phyllachora maydis on Corn, in the United States

Nathan M. Kleczewski University of Illinois at Urbana-Champaign

Diane E. Plewa University of Illinois Extension

Kaitlyn M. Bissonnette University of Missouri

Norman D. Bowman University of Illinois Extension

Joseph LaForest University of Georgia

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This Article is brought to you for free and open access by the Plant Pathology and Microbiology at Iowa State University Digital Repository. It has been accepted for inclusion in Plant Pathology and Microbiology Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Documenting the Establishment, Spread, and Severity of Phyllachora maydis on Corn, in the United States

Abstract 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 eporr ted in the United States. Collaborative efforts to monitor the spread and educate clientele on management are essential as this disease spreads into new areas.

Keywords ascomycete, dispersal, fungi, hybrid, management

Disciplines Agricultural Science | Agriculture | Plant Pathology

Comments This article is published as Kleczewski, Nathan M., Diane E. Plewa, Kaitlyn M. Bissonnette, Norman D. Bowman, Jan M. Byrne, Joseph LaForest, Felipe Dalla-Lana et al. "Documenting the establishment, spread, and severity of Phyllachora maydis on corn, in the United States." Journal of Integrated Pest Management 11, no. 1 (2020): 14. doi:10.1093/jipm/pmaa012.

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Authors Nathan M. Kleczewski, Diane E. Plewa, Kaitlyn M. Bissonnette, Norman D. Bowman, Joseph LaForest, Felipe Dalla-Lana, Dean K. Malvick, Daren S. Mueller, Martin I. Chilvers, Pierce A. Paul, Richard N. Raid, Alison E. Robertson, Gail E. Ruhl, Damon L. Smith, and Darcy E. P. Telenko

This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/plantpath_pubs/323 Journal of Integrated Pest Management, (2020) 11(1): 14; 1–5 doi: 10.1093/jipm/pmaa012 Issues applyparastyle "fig//caption/p[1]" parastyle "FigCapt" applyparastyle "fig" parastyle "Figure" Documenting the Establishment, Spread, and Severity of Phyllachora maydis on Corn, in the United States Nathan M. Kleczewski,1, Diane E. Plewa,2 Kaitlyn M. Bissonnette,3 Norman D. Bowman,2 Jan M. Byrne,4 Joseph LaForest,5 Felipe Dalla-Lana,6, Downloaded from https://academic.oup.com/jipm/article/11/1/14/5871671 by Iowa State University user on 18 August 2021 Dean K. Malvick,7 Daren S. Mueller,8 Martin I. Chilvers,4 Pierce A. Paul,6 Richard N. Raid,9 Alison E. Robertson,8 Gail E. Ruhl,10 Damon L. Smith,11, and Darcy E.P. Telenko10

1Department of Crop Science, University of Illinois, 1101 West Peabody Drive, Urbana, IL, 2Department of Crop Science, University of Illinois Extension, 111 Mumford Hall, 1301 West Gregory Drive, Urbana, IL, 3Division of Plant Sciences, University of Missouri, 110 Waters Hall, Columbia, MO, 4Department of Plant, Soil and Microbial Sciences, Michigan State University, 1066 Bogue Street, East Lansing, MI, 5Center for Invasive Species and Ecosystem Health, University of Georgia, 2360 Rainwater Road, Tifton, GA, 6Department of Plant Pathology, The Ohio State University, 1680 Madison Avenue, Wooster, OH, 7Department of Plant Pathology, University of Min- nesota, 495 Borlaug Hall, St. Paul, MN, 8Department of Plant Pathology and Microbiology, Iowa State University, 2213 Pammel Drive, Ames, IA, 9Institute of Food and Agricultural Sciences, University of Florida, 3200 East Palm Beach Road, Belle Glade, FL 33430, 10De- partment of Botany and Plant Pathology, Purdue University, 915 West State Street, West Lafayette, IN, 11Department of Plant Path- ology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI, and 12Corresponding author, e-mail: [email protected]

Subject Editor: Nathan Walker

Received 25 February 2020; Editorial decision 4 June 2020

Abstract 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.

Key words: ascomycete, dispersal, fungi, hybrid, management

Tar spot, caused by the obligate fungal pathogen Phyllachora Bajet et al. 1994), with symptoms and signs also occurring on leaf maydis Maubl. (Phyllachorales: Phyllachoraceae), is a foliar sheaths and husks in severe cases (Hock et al. 1992, Bajet et al. disease that can cause significant damage to corn throughout 1994). Occasionally, stromata may be surrounded by a necrotic Central America, South America, the Caribbean, and the lesion, giving the lesion a ‘fisheye’ appearance (Kleczewski et al. Midwestern United States (Liu 1973, Bajet et al. 1994, Ruhl et al. 2019a). Although the cause of fisheye lesions is unknown McCoy( 2016, Mottaleb et al. 2018). Initial symptoms appear as small, et al. 2019), severe yield loss of up to 90% has been reported to be chlorotic lesions ~7 d after infection, followed by the develop- associated with these symptoms in Central America (Hock et al. ment of small (0.5–2.5 mm [0.019–0.098] in diameter), gener- 1995, Pereyda-Hernandez et al. 2009, Mahuku et al. 2013). Yield ally circular, brown to black stromata (signs) scattered across the loss resulting from tar spot has been attributed to reduced ear upper and lower leaf surfaces, occasionally coalescing into stripes weight, poor kernel filling, loose kernels, and vivipary, which is a (Liu 1973). Older leaves are most frequently affected (Liu 1973, phenomenon where seeds germinate prematurely before reaching

© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ 1 by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. 2 Journal of Integrated Pest Management, 2020, Vol. 11, No. 1 maturity (Dittrich et al. 1991, Hock et al. 1995). An increase in Distribution of Tar Spot in the United States in the incidence of stalk rots, and a reduction in fodder quality and 2018 and 2019 quantity has also been reported (Bajet et al. 1994, Mahuku et al. Survey data were collected and shared with stakeholders in 2018 2013). and 2019 using different mechanisms. This was due to the need to Tar spot is favored by moderate temperatures (16–21°C [60.8– rapidly acquire data during the sudden tar spot epidemic of 2018, 69.8°F]), a daily average relative humidity of >75%, and at least 7 h whereas the 2019 survey was generally a planned group effort. of free moisture on foliage. Ascospores are produced in perithecia In 2018, state extension specialists manually entered county level within stromata, exuded in a gelatinous matrix, and are believed to incidence data into a shared spreadsheet, and national- and state- be dispersed via wind and rain. After infection and an incubation level maps were manually produced for each state by the state exten- period of 12 to 20 d, new stromata are produced. New ascospores sion specialist using online maps as needed. These maps were shared are produced within these stromata soon thereafter. The fungus with stakeholders through state level extension resources and online Downloaded from https://academic.oup.com/jipm/article/11/1/14/5871671 by Iowa State University user on 18 August 2021 can survive as stromata on residue for at least one winter under on Twitter (https://www.twitter.com). In 2019, state extension spe- Midwestern conditions (Kleczewski et al. 2019a, Groves et al. 2020). cialists reported county-level occurrence of tar spot through an on- In 2015, tar spot was confirmed for the first time in Illinois and line database on the EDDMAPS-maps site (https://corn.ipmpipe.org/ Indiana (Ruhl et al. 2016), and by 2019, it was detected in Florida, tarspot/). Disease incidence and progress maps were shared in real Iowa, Michigan, Ohio, Minnesota, Missouri (K. Bissonette, per- time via map links to state extension websites, Twitter, and direct sonnel communication), and Wisconsin (McCoy et al. 2018, Dalla clientele access to the website. Lana et al. 2019, Malvick et al. 2020). In 2018, persistent, mild and The primary goal of this work was to determine the establish- wet conditions throughout corn reproductive stages presumably fa- ment and spread of tar spot across affected states in the United States. vored the development of tar spot on corn grown in the Midwest. Surveys were conducted by extension specialists, certified crop ad- Field level losses exceeding 3,766 kg/ha (60 bu/A) were reported in visors, industry reps, and other researchers as part of routine field some local areas, with Midwestern losses estimated at ~4,500,000 t checks. Within-field severity and incidence were not assessed in this (177,157,319 bu) in 2018 (Mueller et al. 2019). work. Samples were collected between R5 and R6 in both seasons. Documenting the spread and establishment of plant pathogens Individuals were asked to scout fields as is typical for their operation is important, particularly when the pathogen is new to a particular and provide images and samples of tar spot if it was suspected in a region and management practices by farmers may need to be de- field. Disease confirmation included direct visual observations in the veloped or altered in order to effectively manage the disease and field and by plant samples sent to state extension specialists from associated yield losses. Coordinating large-scale surveys are time extension and industry colleagues, and samples submitted directly consuming, costly, and often impractical. As a result, the spread of to diagnostic clinics. Images of tar spot also were submitted to state these new pathogens may go undocumented, and the diseases that specialists via Twitter with the samples sent to Extension specialists they cause may be misdiagnosed and mismanaged. Prior to 2018, or disease clinics for confirmation. When tar spot was confirmed, no coordinated efforts to document the establishment and spread the county in which it was observed was recorded as positive by of tar spot of corn were conducted. This was, in part, due to late state extension specialists and diagnosticians in the aforementioned season observations of the disease. However, in 2018, researchers platforms. Repeat confirmations within counties were not recorded. in the affected regions pooled knowledge and resources to detect Using these methods, tar spot was confirmed in 173 counties by the and manage this disease in United States corn production regions. end of 2018, and 308 counties in 2019 (Table 1). First detection As part of this effort, surveys were conducted in the affected states of the disease ranged from 26 June in Illinois (IL) to 1 October in in 2018 and 2019 to determine the distribution and spread of tar Ohio (OH) in 2018 and 12 July in Indiana (IN) to 23 October for spot as well as relative disease severity. Here, we present these data, Missouri (MO) in 2019 (Table 1). The counties confirmed by state as well as discuss developments in disease monitoring platforms that ranged from 46 in IL to 4 in Florida (FL) in 2018 and 87 in Iowa (IA) can help farmers determine the proximity of this disease to their to 3 in MO in 2019 (Table 1; Fig. 1). In 2019, tar spot was detected fields during and between seasons.

Table 1. The first observation of disease within a state, number of counties wherePhyllachora maydis was established at the end of 2018, and 2019, and the number of new counties where P. maydis was detected in 2018 and 2019

2018 2019

State First Number of positive Counties with new First Number of positive Counties with new observation counties through 2018 detected infestations observation counties through 2019 detected infestations in 2018 in 2019

Florida 19 June 4 0 20 May 4 0 Illinois 26 June 46 32 20 July 59 13 Indiana 17 Aug. 41 25 12 July 66 25 Iowa 7 Sep. 15 14 19 July 86 71 Michigan 15 July 27 26 26 July 40 13 Minnesota — — — 24 Sep. 4 4 Missouri — — — 23 Oct. 3 3 Ohio 1 Oct. 6 6 3 Oct. 11 5 Wisconsin 10 Jul 34 32 7 Aug. 37 5 Total 173 135 310 139 Journal of Integrated Pest Management, 2020, Vol. 11, No. 1 3 Downloaded from https://academic.oup.com/jipm/article/11/1/14/5871671 by Iowa State University user on 18 August 2021

Fig. 1. Map depicting incidence and spread of tar spot of corn, caused by Phyllachora maydis, in the United States from 2015 to 2019. in 139 new counties, ranging from 71 in IA to 3 in MO (Table 1), in FL to 13.5 in MI, with an overall mean of 3.4% and median of and in two new states, Minnesota (MN) and MO. 1.0% (Table 2). The incidence of fisheye lesions ranged from 0 for all states except FL, to 80.0% in Iowa, with a mean of 1.3% and Tar Spot Symptoms and Severity median of 0%. Less than 6% incidence of fisheye lesions was present To generate baseline data for disease severity in the United States, on the majority of samples assessed (Fig. 2). leaf samples were selected from the middle of the canopy of symp- tomatic plants within affected fields at the R5–R6 growth stages. Samples were placed in plastic or paper bags and shipped to the Discussion University of Illinois plant disease diagnostic laboratory. Upon ar- Tar spot has been present in the United States since 2015, and there rival, samples were pressed and air-dried at room temperature until is a dearth of information about this disease and its management processing. Three leaves per sample were rated for the percentage (Kleczewski et al. 2019b). Economical management of most crop of leaf area with black stromata. The incidence of fisheye lesions diseases is usually achieved through a combination of host resist- was determined for each sample by scoring up to 100 randomly ance, cultural practices, biological control, and informed use of selected stromata for the presence of a fisheye lesion surrounding the chemicals. At present, there are no tar spot resistant hybrids avail- stroma. A similar method was used in 2019, except no specification able in the United States, although relative levels of susceptibility of canopy location was made. All stroma were assessed for fisheye differ among commercial hybrids (Telenko et al. 2019). Recent re- lesions on leaf samples with less than 100 stroma and incidence was search indicates that P. maydis survives the winter in the Midwest on estimated as a proportion of the total stroma inspected. corn residue (Kleczewski et al. 2019a, Groves et al. 2020). This, in In total, 128 samples were received in 2018 from seven states: combination with widespread corn production, often in no-till sys- 52 from Wisconsin (WI), 39 from IL, 20 from IN, 9 from IA, 6 from tems, and increasing evidence that aerial dispersal may be important, OH, and one each from FL and Michigan (MI) (Table 2). All data indicate that tar spot will continue to spread and pose a significant are rounded down for simplicity. The severity of P. maydis stro- threat to corn production in the United States. Increased awareness mata ranged from 0.5% in IL, IN, IA, and OH, to 66.7% in WI. and educational efforts to enable farmers to make informed deci- Mean severity levels ranged from 2.2% in OH to 12.5% in IL, with sions for tar spot management will enhance our ability to identify an overall mean of 10.8% and median of 5.0%. The incidence of the establishment and spread of this disease. It is essential that this fisheye lesions ranged from 0 in IA and OH to 11.5% in IL, with an disease continues to be tracked to reduce potential on-farm losses overall mean of 0.5% and median of 0 (Table 2). Mean incidence of and simultaneously avoid unneeded fungicide inputs if the disease fisheye lesions ranged from 0 in IA and OH to 0.8% in IL, with an is absent. overall mean of 0.5% and median of 0. In this work, we demonstrated that the use of a collabora- In 2019, 191 samples were collected from seven states: 2 from tive network of stakeholders, researchers, and other members of FL, 36 from IA, 25 from IL, 101 from IN, 5 from MI, 5 from MN, the agricultural community can be successfully coordinated to and 17 from WI (Table 2). The severity of P. maydis stromata ranged produce accurate and timely disease tracking maps, improving from <0.1% in WI to 35% in IN. Mean severities ranged from 1.0% overall turnaround time and reporting, while reducing resource 4 Journal of Integrated Pest Management, 2020, Vol. 11, No. 1

Table 2. Overall and state-by-state summary statistics for stromata severity and fisheye lesion incidence associated with leaf samples submitted for tar spot assessment in 2018 and 2019

Location Number of Stromata severity (%) Fisheye lesion incidence samples (% stromata with lesion)

Mean SE Median Range Mean SE Median Range

2018 Overall 128 10.8 1.3 5.0 0.5–66.7 0.5 0.1 0.0 0–11.5 Illinois 39 12.5 2.5 5.0 0.5–56.6 0.8 0.4 0.0 0–11.5 Indiana 20 10.2 3.0 3.7 0.5–56.7 0.1 0.1 0.0 1.3

Iowa 9 6.2 2.2 6.7 0.5–16.7 0.0 0.0 0.0 0–0.1 Downloaded from https://academic.oup.com/jipm/article/11/1/14/5871671 by Iowa State University user on 18 August 2021 Ohio 6 2.2 0.8 1.0 0.5–5.3 0.0 0.0 0.0 0.0 Wisconsin 52 11.4 2.1 6.7 0.6–66.7 0.5 0.2 0.0 0–5.5 2019 Overall 191 3.4 6.5 1.0 <0.1–35 1.3 6.9 0.0 0–80.0 Florida 2 1.0 0.0 1.0 1.0–1.0 10.4 2.2 10.4 8.8–12.0 Illinois 25 5.0 5.9 2.3 0.7–25.0 1.8 4.9 0.0 0–23.1 Indiana 101 2.1 6.4 0.1 0.1–35.0 0.9 4.3 0.0 0–33.3 Iowa 36 3.0 5.4 1.0 0.1–30.0 2.3 13.3 0.0 0–80.0 Michigan 5 13.5 6.5 10.3 7.0–21.7 1.7 1.9 1.1 0–4.2 Minnesota 5 8.7 7.1 13.3 1.0–15.0 0.2 0.5 0.0 0–1.2 Wisconsin 17 5.5 6.6 <0.1 <0.1–25.0 0.2 0.6 0.0 0–2.5

Only states submitting more than one sample in a year are included. Data are rounded down to the nearest decimal place.

to track the movement of pests and pathogens including tar spot (https://www.eddmaps.org/). Traditional methods to survey plant pathogens are costly, time consuming, and labor intensive. These methods include 1) in-field assessments, 2) spore trapping, and 3) the use of sentinel plots (Sikora et al. 2014). Field-level surveys may be limited to individuals wishing to participate in the survey, or fields located in areas near travel routes, thereby being somewhat limited. Furthermore, the amount of resources required to conduct a coordinated survey are usually substantial, and many states lack the infrastructure to complete them. Plant pathogens cannot be lured or trapped like in- sect pests (e.g., Lagos-Kutz and Voegtlin 2016). Although P. maydis spores could be potentially identified and quantified using spore traps, this technology would not only be time consuming but would also require considerable resources, including the development of a species-specific qPCR technology, dedicated laboratories to conduct the analyses, and funds to set up and collect data from Fig. 2. Histogram showing the incidence of fisheye lesions from 191 samples spore traps. Furthermore, the number and location of spore traps collected across seven states in 2019. also is resource limited, and delivery of data to the public delayed by sample processing. Another traditional survey method used and funding input. This method improved the ability of extension in monitoring pathogen spread involves the use of sentinel plots specialists to not only communicate tar spot distribution with (e.g., Sikora et al. 2014). These are often small plots of a suscep- their clientele but also improve the timeliness of that communica- tible host that are maintained without fungicide applications and tion. In 2018, the generation of tar spot incidence maps was labor monitored periodically throughout the season for the presence of intensive, and extension specialists and those in the agricultural disease. As with spore-trapping methods, the number and location community were only able to obtain information as it was slowly of sentinel plots is constrained by personnel and time, and positive posted online. Data needed to be checked by extension specialists disease confirmation requires assessment by diagnostic clinics or for accuracy, and observations added after disease confirmation. specialized laboratories. In this study, we maximized observations In 2019, the EDDMAPS platform enabled each state specialist to and minimized time-consuming traditional survey methodology by rapidly and easily enter observation data, which was then publicly working collaboratively with extension, government, industry, and available in real time on the incidence map. The use of this system producers, to efficiently determine pathogen presence and spread. greatly increased the efficiency and effectiveness of mapping This was accomplished by coordination of efforts across state disease spread in the 2019 season. The EDDMAPS platform has lines and amongst agricultural professionals, allowing efficient, been adapted for use in several systems, including southern corn real-time dissemination of observations to the agricultural com- rust, spotted wing drosophila, and purple loosestrife. The plat- munity. Supplementing extension observations with social media form has provided an effective and efficient means for specialists has been successful for other corn diseases (Mueller et al. 2018), Journal of Integrated Pest Management, 2020, Vol. 11, No. 1 5 and in our experience, it also helped with documenting the spread Hock, J., U. Dittrich, B. Renfro, and J. Kranz. 1992. Sequential development of P. maydis. of pathogens in the maize tarspot disease complex. Mycopathologia 117: Our data indicate that the incidence of fisheye lesions was gen- 157–161. erally low or absent in most survey samples, and data indicate that Hock, J., J. Kranz, and B. Renfro. 1995. Studies on the epidemiology of the tar spot disease complex of maize in Mexico. Plant Pathol. 44: 490–502. severe tar spot outbreaks and subsequent yield losses can occur Kleczewski, N. M., J. Donnelly, and R. Higgins. 2019a. Phyllachora maydis, without the presence of fisheye lesions (Liu 1973, Telenko et al. causal agent of tar spot on corn, can overwinter in Northern Illinois. Plant 2019). Phyllachora spp. are known to significantly reduce photo- Health Prog. 20: 178. synthesis and productivity of their hosts, alter the position and size Kleczewski, N. M., M. Chilvers, D. S. Mueller, D. Plewa, A. E. Robertson, of vascular bundles in foliage depending on the location of infec- D. L. Smith, and D. Telenko. 2019b. Corn disease management: tion and species of plant host, and colonize the vascular bundles, tar spot. Crop Protection Network CPN 2012-W. doi:10.31274/ xylem, and phloem of warm-season grasses (Parbery 1963, Gabel cpn-20190620-00808 Downloaded from https://academic.oup.com/jipm/article/11/1/14/5871671 by Iowa State University user on 18 August 2021 1989). It appears likely that similar effects occur in corn infected Lagos-Kutz, D., and D. Voegtlin. 2016. Aphid suction trap network. Farm with P. maydis, and severe infections compromise leaf function and Progress Rep 2015: 66. water/nutrient movement in the leaf. More detailed studies assessing Liu, L.-J. 1973. Incidence of tar spot disease of corn in Puerto Rico. J. Agric. Univ. Puerto Rico 42: 211–216. the infection process are needed to better understand how P. maydis Mahuku, G., R. Shrestha, and F. San Vicente. 2013. Tar spot complex of maize: affects the physiology, anatomy, and productivity of corn. Facts and actions. www.researchgate.net/publication/266732736_Tar_ This work indicates that tar spot is spreading and poses a sig- Spot_Complex_of_Maize_Facts_and_Actions. Accessed 8 March 2020. nificant threat to corn production in the United States. Coordinated Malvick, D. K., D. E. Plewa, D. Lara, N. M. Kleczewski, C. M. Floyd, and efforts to monitor continued spread will be essential in ensuring B. E. Arenz. 2020. First report of tar spot of corn caused by Phyllachora that farmers and the agronomic community are educated in areas of maydis in Minnesota. Plant Dis. 104: 1865–1865. greatest risk and in disease identification and disease management McCoy, A. G., M. K. Romberg, E. R. Zaworski, A. F. Robertson, A. Phibbs, and mitigation techniques. This work highlights the importance of B. D. Hudelson, D. L. Smith, R. L. Beiriger, R. N. Raid, J. M. Byrne, et al. 2018. coordinated, cooperative efforts of extension personnel, farmers, First report of tar spot on corn (Zea mays) caused by Phyllachora maydis in government, and industry in the management of tar spot on corn. Florida, Iowa, Michigan, and Wisconsin. Plant Dis. 102: 1851–1852. McCoy, A., M. Roth, R. Shay, Z. Noel, M. Jayawardana, R. Longley, G. Bonito, and M. Chilvers. 2019. Identification of fungal communities within the tar spot complex of corn in Michigan via next-generation sequencing. Phytobiobes Acknowledgments J. 3: 235–243. We thank Chase Kangas, Keith Ames, Terence Lo, Zach Duray, Brian Hudelson, Mottaleb, K. A., A. Loladze, K. Sonder, G. Kruseman, and F. San Vicente. 2018. Carol Groves, Brian Mueller, Gail Ruhl, Tom Creswell, Ed Zaworski, and Threats of tar spot complex disease of maize in the United States of America Felipe Dalla Lana da Silva for assisting with sample processing and the nu- and its global consequences. Mitig Adapt. Strat. Global Change 24: 1–20. merous cooperators who assisted in providing samples and images used in Mueller, D. S., A. J. Sisson, R. Kempker, S. Isard, C. Raymond, A. J. Gennett, developing these data. Thank you to Nick Seiter, Adam Sisson, Yuba Kandel, W. Sheffer, and C. A. Bradley. 2018. Scout, snap, and share: first impres- and Zach Duray for editorial suggestions on previous drafts of this manu- sions of plant disease monitoring using social media. Plant Dis. 102: script. Partial funding for this work was provided through a Foundation for 1681–1686. 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