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    Mechanistic links between physiology and spectral reflectance enable pre-visual detection of oak wilt and drought stress
    (Proceedings of the National Academy of Sciences, 2024-02) Sapes, Gerard; Schroeder, Lucy; Scott, Allison; Clark, Isaiah; Juzwik, Jennifer; Montgomery, Rebecca; Guzmán Q., J. Antonio; Cavender-Bares, Jeannine
    Tree mortality due to global change—including range expansion of invasive pests and pathogens—is a paramount threat to forest ecosystems. Oak forests are among the most prevalent and valuable ecosystems both ecologically and economically in the United States. There is increasing interest in monitoring oak decline and death due to both drought and the oak wilt pathogen (Bretziella fagacearum). We combined anatomical and ecophysiological measurements with spectroscopy at leaf, canopy, and airborne levels to enable differentiation of oak wilt and drought, and detection prior to visible symptom appearance. We performed an outdoor potted experiment with Quercus rubra saplings subjected to drought stress and/or artificially inoculated with the pathogen. Models developed from spectral reflectance accurately predicted ecophysiological indicators of oak wilt and drought decline in both potted and field experiments with naturally grown saplings. Both oak wilt and drought resulted in blocked water transport through xylem conduits. However, oak wilt impaired conduits in localized regions of the xylem due to formation of tyloses instead of emboli. The localized tylose formation resulted in more variable canopy photosynthesis and water content in diseased trees than drought-stressed ones. Reflectance signatures of plant photosynthesis, water content and cellular damage detected oak wilt and drought 13 days before visual symptoms appeared. Our results show that leaf spectral reflectance models predict ecophysiological processes relevant to detection and differentiation of disease and drought. Coupling spectral models that detect physiological change with spatial information enhances capacity to differentiate plant stress types such as oak wilt and drought.
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    Economic-threshold-based classification of soybean aphid, Aphis glycines, infestations in commercial soybean fields using Sentinel-2 satellite data
    (Crop Protection, 2023-12) Ribeiro, Arthur V.; Lacerda, Lorena N.; Windmuller-Campione, Marcella A.; Cira, Theresa M.; Marston, Zachary P.D.; Alves, Tavvs M.; Hodgson, Erin W.; MacRae, Ian V.; Mulla, David J.; Koch, Robert L.
    The soybean aphid (SBA), Aphis glycines Matsumura (Hemiptera: Aphididae), is a significant insect pest of soybean, Glycine max (L.) Merrill (Fabales: Fabaceae), and field treatment decisions for this pest are based on average field populations. Previous studies indicated that ground- and drone-based red-edge and near-infrared remote sensing can be used to detect plant stress caused by SBA infestations in soybean. However, it remains to be determined if remote sensing for SBA can be expanded to field or landscape scale using satellite-based platforms. Thus, this research was conducted in three steps to determine the potential of using Sentinel-2 satellite data for the classification of SBA infestations in soybean fields using simulated and actual Sentinel-2 satellite spectral reflectance. In the first step, as a proof of concept, hyperspectral data from cage studies were used to simulate Sentinel-2 bands and vegetation indices (VIs), conducted in nine trials at multiple locations between 2013 and 2021. The effects of SBA from caged plants on simulated data were evaluated with random intercept linear mixed models. The satellite simulation indicated a significant effect of SBA on the spectral reflectance of caged soybean plants (p < 0.05) for four satellite bands (5, 6, 7, and 8A) and five VIs (NDVI, GNDVI, SAVI, OSAVI, and NDRE). In the second step, actual Sentinel-2 spectral reflectance and corresponding aphid counts of commercial soybean fields, collected from 2017 to 2019, were obtained. The relationship between SBA counts and Sentinel-2 spectral reflectance from commercial soybean fields were evaluated with general linear models. A significant effect of SBA was observed for three satellite bands (6, 7, and 8A) and three VIs (NDVI, SAVI, and OSAVI). In the third step, linear support vector machine (LSVM) models for the classification of SBA infestations as above or below a previously determined economic threshold of 250 aphids per plant were developed using simulated Sentinel-2 bands and VIs from the caged plots, and were tested on actual Sentinel-2 data from commercial soybean fields. The best LSVM model for the classification of aphids in soybean reached 91% accuracy, 85.7% sensitivity, and 93.3% specificity. Thus, simulations with caged plots can be used as an indication of the potential of using satellite data for the detection of plant stresses on a larger scale. Furthermore, this study advances decision-making for SBA, and the developed LSVM model can be used to update regional and local monitoring for the management of SBA.
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    Opportunities and challenges in advanced communication technologies in the environment: A case of forest management communications
    (Applied Environmental Education & Communication, 2023-12-11) Tsakakis, Elena; Gupta, Angela; Schneider, Ingrid E.
    Advanced information communication technologies (ICT) offer significant benefits to applied communications, including potential cost reductions, service improvements, and expanded natural resource education in an era of ever-decreasing budgets. Limited guidance exists about how to design and implement virtual reality and augmented reality experiences in environmental spaces but clearly it takes time, expertise, equipment, and iterative feedback with experts and users. Our 18-month collaborative development process used best practices, stakeholder involvement, and multimedia teams to create and test augmented reality and virtual reality visitor education about forest management. Based on this effort, we share challenges, opportunities, and ideas to implement ICT in applied environmental education.
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    Can Co-Grazing Waterfowl Reduce Brainworm Risk for Goats Browsing in Natural Areas?
    (EcoHealth, 2022) Marchetto, Katherine M.; Linn, Morgan M.; Larkin, Daniel J.; Wolf, Tiffany M.
    Goats browsing in woodlands, whether for livestock production goals or vegetation management (e.g., targeted grazing to control invasive plants), are at risk of meningeal worm ( Parelaphostrongylus tenuis ) infection. Indeed, up to 25% incidence has been observed in goats employed in vegetation management. Infection, which occurs via the consumption of an infected gastropod intermediate host, is potentially deadly in goats. We experimentally tested whether co-grazing with waterfowl could reduce goats’ exposure via waterfowl consumption of gastropods. Gastropods were sampled in a deciduous woodland before and after the addition of goats alone, goats and waterfowl, or a control with no animal addition. We found that goats browsing on their own increased the abundance of P. tenuis intermediate hosts; however, when goats co-grazed with waterfowl, these increases were not observed. Importantly, waterfowl did not significantly affect overall gastropod abundance, richness, or diversity. Thus, waterfowl co-grazing may effectively reduce goat contact with infectious gastropods without detrimentally affecting the gastropod community. While co-grazing goats with waterfowl may decrease their P. tenuis exposure risk, additional research is needed to confirm whether waterfowl can actually lower P. tenuis incidence.
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    The effectiveness of using targeted grazing for vegetation management: a meta-analysis
    (Restoration Ecology, 2021) Marchetto, Katherine M.; Wolf, Tiffany M.; Larkin, Daniel J.
    The use of targeted grazing to control undesired plants as a component of ecological restoration is gaining in popularity, but there is considerable uncertainty among land managers about the effectiveness of this approach. We synthesized existing literature on the use of livestock (ruminants, swine, and equids) to control undesired plants using a meta‐analysis to address questions about the effectiveness of the approach. Seventy studies matched our inclusion criteria; these comprised 86% peer‐reviewed journal articles and 14% gray literature. Studies were conducted in 17 countries but highly concentrated in the United States and Europe. Cattle, goats, horses, and sheep were used for vegetation management in the studies. Most target plant species were nonnative perennial forbs. Median study duration was 3 years, with a maximum of 10 years. We found that, overall, the use of targeted grazing significantly reduced undesired plants and significantly increased plant species richness. However, several important questions remain. In particular, further research is needed to differentiate temporary defoliation from actual plant mortality, to separate the contributions of native versus nonnative species to gains in plant species richness, and to address longer term outcomes following grazing cessation.
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    Goat Digestion Leads to Low Survival and Viability of Common Buckthorn (Rhamnus cathartica) Seeds
    (Natural Areas Journal, 2020) Marchetto, Katherine M.; Heuschele, D. Jo; Larkin, Daniel J.; Wolf, Tiffany M.
    The use of goat browsing for invasive plant management is growing in the United States, but many questions remain about the efficacy of goat browsing for invasive plant control. One common concern of land managers and other stakeholders is whether goats can spread invasive plants through endozoochory (seed dispersal via ingestion and excretion in feces). We evaluated this possibility using common buckthorn (Rhamnus cathartica), an invasive shrub for which goats are often employed as a control method. Goats were fed buckthorn berries, and their feces were collected and examined at 24 hr, 48 hr, and 72 hr post-ingestion for intact seeds that survived gut passage. A low proportion of buckthorn seeds (2%) made it through the goat digestive system intact. Of these, only 11% remained viable, compared to 63% viability of control seeds. We conclude that consumption of buckthorn fruits by goats effectively destroys seeds, indicating low risk of dispersal via gut passage. To put these results in context, and provide more guidance for land managers, we additionally reviewed literature investigating seed recovery following ingestion by goats. Based on a synthetic analysis across 28 plant species, we found that seeds >4 mm long were unlikely to be recovered from feces intact, while smaller seeds posed higher dispersal risk.
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    Foliage Type and Deprivation Alters the Movement Behavior of Late Instar European Gypsy Moth Lymantria dispar (Lepidoptera: Erebidae)
    (Journal of Insect Behavior, 2019-04) Wittman, Jacob T.; Aukema, Brian H.
    The movement behavior of insects characterizes their ability to disperse, establish, compete, forage, seek mates, and ultimately reproduce. Understanding the movement of invasive insects is particularly important for developing management policies. We conducted laboratory experiments in Minnesota, USA to determine how host type and food deprivation affected the movement of late instars of the European gypsy moth Lymantria dispar (Lepidoptera: Erebidae), an invasive forest insect in North America. Gypsy moth larvae can feed on over 300 species of trees and shrubs. During outbreaks food availability to conspecifics can become severely restricted as developing instars consume increasing amounts of foliage. Larvae were raised on one of five foods: Quercus macrocarpa , Larix laricina , Acer platanoides , Acer saccharinum , or artificial diet. Subsets of fifth and sixth instar larvae were also deprived of food for zero, 24, or 48 h. After the food deprivation period, late instar larvae were placed on a servosphere and their movement paths were recorded. Larvae raised on Q. macrocarpa , a preferred host, were unlikely to move unless starved. They moved farther the longer they were starved. In contrast, when larvae were raised on less preferred hosts, they were more likely to move without prior starvation. These results suggest that feeding on optimal hosts provides gypsy moth larvae with the energy and nutritional requirements to move more quickly to more food when there is none immediately available.
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    Effects of systemic insecticides against emerald ash borer on ash seed resources
    (Forest Ecology and Management, 2022-05) Mwangola, Dorah M.; Kees, Aubree M.; Grosman, Donald M.; Aukema, Brian H.
    Emerald ash borer (EAB), Agrilus planipennsis, is an invasive insect that was accidentally introduced to North America from Asia. It continues to spread rapidly across North America and is responsible for the death of tens of millions of ash trees (Fraxinus spp.). All North American species of ash are susceptible to EAB infestation threatening the ash resource and diversity. Measures such as systemic insecticide treatments in urban forests and collection of ash seeds provide a means of conserving genetic resources. Understanding the effect these insecticides could have on ash seed viability is therefore important to informing conservation efforts. Another potential concern for effective conservation of ash seeds is the ash seed weevil (Lignyodes spp.) whose larvae develop in and feed on ash seeds. However, the effect of EAB insecticides on weevil infestation levels in ash seeds has not been investigated to date. Our study investigated the effect of two systemic insecticide treatments, azadirachtin and emamectin benzoate, on levels of ash seed weevil infestation, seed germination ability, and seed germination time of seeds collected from boulevard trees of green ash (F. pennsylvanica Marsh.) in cities in Minnesota from 2017 to 2019. Weevil infestation levels were similar between untreated and treated trees in 2017 and 2018. In 2019, the weevil prevalence in untreated trees was on average 17% and 30% higher than in azadirachtin and emamectin benzoate-treated trees respectively. Weevil infestation data suggests that repeated insecticide treatments at labelled rates can reduce seed weevils that target germplasm. Additionally, insecticide treatments did not affect ash seed germination rates between treatments. These results suggest that systemic insecticides may be effective at conserving the seed resource in addition to known benefits such as canopy preservation.
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    The Impact of Systematic Insecticides Against Emerald Ash Borer on Phenology of Urban Ash Trees
    (Journal of Economic Entomology, 2023-02) Mwangola, Dorah M.; Kees, Aubree M.; Grosman, Donald M.; Aukema, Brian H.
    The continued threat of emerald ash borer (Agrilus planipennis; EAB) to North American ash trees (Fraxinus spp.) has necessitated the use of systemic insecticide treatments as a primary control strategy against EAB in urban centers. Altered tree phenology due to systemic insecticides could mediate nontarget effects on other insect species, such as seed weevils or leaf-feeders, but whether such injections alter phenological events has not been studied.This study assessed the effects of systemic injections of emamectin benzoate or azadirachtin relative to untreated controls on the spring and fall phenology of mature green ash trees in Saint Paul, MN, USA from fall 2017 to spring 2019. EAB was first detected in this area in 2009.Trees showed minor, visible signs of EAB infestation at study initiation, but not mortality. We examined six phenological events: bud swelling, budburst, flowering, leaf out, leaf color change, and leaf abscission using a visual survey protocol.The timing of phenological events was similar across the different treatments for all but two of events; budburst and flowering. Budburst and flowering occurred 7 d and 5 d earlier, respectively, in treated trees than untreated trees. Given symptoms observed, we posit that delays in these events in untreated trees were due to infestations of EAB and the treatments of emamectin benzoate or azadiractin simply preserved the original phenology.The results from this study suggest that systemic insecticides may mitigate changes in ash tree phenology such as delayed leaf out that may be early symptoms of emerald ash borer.
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    Defensive response of evolutionarily naïve Pinus sylvestris to the mountain pine beetle fungal associate Grosmannia clavigera in comparison to Pinus ponderosa
    (Forest Ecology and Management, 2023-10) Chase, Kevin D.; Rynders, Kathryn J.; Maddox, Mitchell P.; Aukema, Brian H.
    Mountain pine beetle (MPB, Dendroctonus ponderosae) is a destructive pest of pine forests in western North America. This insect is currently expanding its range across the Canadian boreal forest towards eastern North America, where a suite of novel pine species will be encountered. One species of pine without prior association with MPB is Pinus sylvestris (Scots pine), which is native to Europe and naturalized in parts of central and eastern North America. Here, we take advantage of a unique opportunity in the Black Hills of South Dakota where an isolated, planted, and mature stand of P. sylvestris and native Pinus ponderosa (ponderosa pine) co-exist within the range of MPB. We conducted a punch-inoculation experiment to determine the chemical response of P. sylvestris from a blue-stain fungus associated with MPB, Grosmannia clavigera, and compared the response to that of P. ponderosa. We found that P. sylvestris had a higher localized monoterpene response than P. ponderosa in response to inoculation, but a lower sesquiterpene response. Among the significant monoterpenes associated with MPB behavior, limonene, 3-carene, and myrcene had a larger localized response in P. sylvestris than P. ponderosa; lower levels of 4-allylanisole were found in P. sylvestris. Fungal inoculation did not induce a stronger terpenoid response than mechanical wounding without inoculation, indicating that P. sylvestris responds to mechanical damage similarly as to fungal inoculation. Pinus sylvestris may provide one alternative plantation species for timber production in the Great Lakes Region following mountain pine beetle incursion, however, more evaluation is needed to determine the role of this species in future plantings.
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    Colonization and reproduction of potential competitors with mountain pine beetle in baited logs of a new host for mountain pine beetle, jack pine
    (Forest Ecology and Management, 2021-10) Smith, Zach M.; Chase, Kevin D.; Takagi, Esturo; Kees, Aubree M.; Aukema, Brian H.
    The mountain pine beetle (Dendroctonus ponderosae Hopkins) is a bark beetle that is native to pine forests of western North America and the Black Hills of South Dakota. Recent eastward range expansion into stands of jack pine (Pinus banksiana) and associated hybrids with lodgepole pine (Pinus contorta) in western Canada has created concern that the insect will continue moving eastward. In the Great Lakes region, mountain pine beetle would encounter novel species of pines and associated insect fauna; interactions with which are largely unexplored. We baited logs of jack pine with lures for mountain pine beetle and Ips grandicollis (Eichhoff) alone and in combination in a 2 × 2 factorial design in the Black Hills of South Dakota. Both insects occur in this region, but not jack pine, a common species in the Great Lakes region of North America at risk of invasion by mountain pine beetle. We measured attraction and reproduction of insects that colonized the logs. Ips grandicollis were significantly more attracted to logs of jack pine baited with their aggregation pheromone, ipsenol, than unbaited logs or those baited with pheromones of mountain pine beetle and myrcene, a host volatile. Colonization by I. grandicollis was inhibited by the presence of lures for mountain pine beetle. We also found larvae of longhorn borers, likely ­ Monochamus spp., infesting logs. These borers, which act as competitors and facultative predators of bark beetles, were significantly attracted to logs baited with ipsenol over those baited with lures for mountain pine beetle. Our results suggest that if mountain pine beetle were to invade the Great Lakes Region, common bark and wood-boring species such as I. grandicollis and longhorn borers would not compete with mountain pine beetles at tree-colonizing stages, and thus could pose little resistance to invasion.
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    Landscape-level likelihood estimation of eastern spruce dwarf mistletoe (Arceuthobium pusillum) infestations in lowland black spruce (Picea mariana) forests of Minnesota, USA
    (Canadian Journal of Forest Research, 2023-10) Gray, Ella R.; Russell, Matthew B.; Windmuller-Campione, Marcella Anna
    Biotic disturbance agents are important factors influencing forest dynamics; incorporating them into management planning requires detailed understanding of their distribution, prevalence, and effects on stand dynamics. However, this information can be difficult to collect in remote forest systems, such as lowland black spruce (Picea mariana (Mill.) B. S. P.) forests affected by eastern spruce dwarf mistletoe (Arceuthobium pusillum Peck, hereafter ESDM). In such cases, predictive modeling is often needed to inform management decisions and address forest health questions. Here, we used two publicly available datasets to predict areas where black spruce is more likely to be infested with ESDM in northeastern Minnesota, USA. Using random forest modeling and logistic regression, we found location, stand age, basal area, site index, average diameter, and metrics of species composition to be among the most important predictors of ESDM occurrence. Predictions showed two regions of greater likelihood of infestation with distinct ecological characteristics and ownership patterns. By understanding how stand structural characteristics relate to ESDM infestations, managers can improve monitoring and management of ESDM at the stand and landscape scales. Additionally, our approach of using multiple datasets and modeling methods can serve as a framework for decision making for other forest health concerns.
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    Cold tolerance and overwintering survival of Aphelinus certus (Hymenoptera: Aphelinidae), a parasitoid of the soybean aphid (Hemiptera: Aphididae) in North America
    (Bulletin of Entomological Research, 2023-06) Stenoien, Carl M.; Christianson, Lindsey; Welch, Kelton; Dregni, Jonathan; Hopper, Keith R.; Heimpel, George E.
    Broad-spectrum insecticides are the main control measure of the invasive and economically damaging soybean aphid (Aphis glycines) in North America, although biological control by resident natural enemies can also greatly diminish population levels. One such natural enemy is the accidentally introduced Eurasian parasitoid Aphelinus certus (Hymenoptera: Aphelinidae), though its impact appears to be limited by low rates of parasitism early in the growing season. We tested the hypothesis that A. certus might experience high overwintering mortality. In the laboratory, we used thermocouple thermometry to measure the supercooling points of diapausing parasitoids and assessed parasitoid survival after exposure to ecologically relevant durations of low temperature. We found A. certus to be freeze-intolerant with a median supercooling point of -28 & DEG;C. When exposed to temperatures of 0 & DEG;C for up to 7 months, adults emerged only after exposures of at least 60 days and survival decreased with durations beyond 150 days. We also conducted in-field studies at sites from northern Minnesota to southern Iowa to determine if diapausing A. certus could overwinter above and below the snowpack. Survival was negatively correlated with increasing latitude and was greater for parasitoids placed on the ground than 1 meter off the ground, likely due to the warmer and stabler temperatures of the subnivean microclimate. Our results suggest that A. certus is capable of overwintering in the region inhabited by soybean aphid but may experience substantial mortality even under ideal conditions. Climate change is predicted to bring warmer, drier winters to the North American Midwest, with decreased depth and duration of snow cover, which may further reduce overwintering survival.
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    A field-based assessment of the parasitoid Aphelinus certus as a biological control agent of soybean aphid in North America
    (Biological Control, 2020) Miksanek, James Rudolph; Heimpel, George E.
    Damaging outbreaks of soybean aphid continue to occur in North America despite the valuable biological control services provided by resident natural enemies. The adventive parasitoid Aphelinus certus Yasnosh (Hymenoptera: Aphelinidae) has recently established in North America and has been hypothesized to be a key component of the resident natural enemy community, but there have been few studies evaluating the efficacy of this parasitoid in suppressing soybean aphid populations. We used an exclusion cage study to quantify the effect of A. certus on soybean aphid population growth at four sites spanning western and east-central Minnesota from 2017 to 2019. There were minimal differences in soybean aphid population growth between experimental treatments that excluded natural enemies and control treatments, suggesting that parasitism of soybean aphid by A. certus did not have a strong impact on soybean aphid population growth during this study. Because, for example, A. certus larvae can reduce host reproduction prior to mortality (resulting in underestimates of effects in short-term studies), our results reflect the challenges of using exclusion cages to assess the effects of individual natural enemy species, especially those with complex life cycles.
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    Density-dependent lifespan and estimation of life expectancy for a parasitoid with implications for population dynamics
    (Oecologia, 2020) Miksanek, James Rudolph; Heimpel, George E.
    Parasitoid lifespan is influenced by nutrient availability, thus the lifespan of parasitoids that rely on their hosts for nutritional resources (either via host feeding or by consuming honeydew) should vary with host density. We assessed the survival and reproduction of one such species, Aphelinus certus— a parasitoid of the soybean aphid, Aphis glycines —over a range of host densities using a laboratory assay. We found a positive, asymptotic relationship between host density and the lifespan and fecundity of A. certus that was supported by a traditional survivorship analysis as well as a logistic model. Parasitoids from this assay were also used to develop a wing wear index relating setae damage to parasitoid age. This index was used to estimate the life expectancy of field-collected parasitoids, which was shorter than the life expectancy of laboratory-reared female parasitoids. Finally, host-density-dependent parasitoid lifespan was incorporated into a coupled-equations matrix population model that revealed that decreasing the degree of host density dependence leads to higher equilibrium host densities and changes in the quality of equilibrium (e.g. stable limit cycles). These results detail the relatively unstudied phenomenon of host-density-dependent parasitoid lifespan and suggest that differences between laboratory- and field-determined parasitoid life expectancy have important implications for population dynamics and the biological control of insects.
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    A new and effective method to induce infection of Phyllachora maydis into corn for tar spot studies in controlled environments
    (Plant Methods, 2023) Solórzano, José E.; Issendorf, Shea E.; Drott, Milton T.; Check, Jill C.; Roggenkamp, Emily M.; Cruz, C. D.; Kleczewski, Nathan M.; Gongóra-Canul, Carlos C.; Malvick, Dean K.
    Background Tar spot of corn is a significant and spreading disease in the continental U.S. and Canada caused by the obligate biotrophic fungus Phyllachora maydis. As of 2023, tar spot had been reported in 18 U.S. states and one Canadian Province. The symptoms of tar spot include chlorotic flecking followed by the formation of black stromata where conidia and ascospores are produced. Advancements in research and management for tar spot have been limited by a need for a reliable method to inoculate plants to enable the study of the disease. The goal of this study was to develop a reliable method to induce tar spot in controlled conditions. Results We induced infection of corn by P. maydis in 100% of inoculated plants with a new inoculation method. This method includes the use of vacuum-collection tools to extract ascospores from field-infected corn leaves, application of spores to leaves, and induction of the disease in the dark at high humidity and moderate temperatures. Infection and disease development were consistently achieved in four independent experiments on different corn hybrids and under different environmental conditions in a greenhouse and growth chamber. Disease induction was impacted by the source and storage conditions of spores, as tar spot was not induced with ascospores from leaves stored dry at 25 degrees C for 5 months but was induced using ascospores from infected leaves stored at -20 degrees C for 5 months. The time from inoculation to stromata formation was 10 to 12 days and ascospores were present 19 days after inoculation throughout our experiments. In addition to providing techniques that enable in-vitro experimentation, our research also provides fundamental insights into the conditions that favor tar spot epidemics. Conclusions We developed a method to reliably inoculate corn with P. maydis. The method was validated by multiple independent experiments in which infection was induced in 100% of the plants, demonstrating its consistency in controlled conditions. This new method facilitates research on tar spot and provides opportunities to study the biology of P. maydis, the epidemiology of tar spot, and for identifying host resistance.
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    Tar Spot of Corn: A Diagnostic and Methods Guide
    (Plant Health Progress, 2023) Solórzano, José E.; Cruz, C. D.; Arenz, Brett E.; Malvick, Dean K.; Kleczewski, Nathan M.
    Tar spot of corn is an emerging plant disease in the continental United States and Canada caused by the fungal pathogen Phyllachora maydis Maubl. Tar spot has been known to occur in Mexico, the Caribbean, and Central and South America since the early to mid-1900s. In 2015, it was reported for the first time in the continental United States. Since that time, tar spot has spread across corn-producing areas in the United States with epidemics as recent as 2021 resulting in significant yield losses. Although tar spot has been known to affect corn for over a century in the Americas, the biology of the pathogen, etiology, and epidemiology of the disease are not well understood. Additionally, symptoms and signs of tar spot resemble other foliar diseases and abiotic disorders of corn, which may lead to misdiagnosis. In this paper, we provide a brief description of current knowledge about tar spot of corn, including pathogen taxonomy, host range, symptoms and signs, specimen storage, pathogenicity testing, diagnostic protocols, and geographic distribution. This information will be useful to diagnosticians, researchers, and other professionals working with this disease.
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    Genetic Diversity and Aggressiveness of Fusarium virguliforme Isolates Across the Midwestern United States
    (Phytopathology, 2022) Olarte, Rodrigo A.; Hall, Rebecca; Tabima, Javier F.; Malvick, Dean; Bushley, Kathryn
    Sudden death syndrome (SDS) of soybean is a damaging disease caused by the fungus Fusarium virguliforme. Since this pathogen was first reported in the southern U.S. state of Arkansas in 1971, it has spread throughout the midwestern United States. The SDS pathogen primarily colonizes roots but also produces toxins that translocate to and damage leaves. Previous studies have detected little to no genetic differentiation among isolates, suggesting F. virguliforme in North America has limited genetic diversity and a clonal population structure. Yet, isolates vary in virulence to roots and leaves. We characterized a set of F. virguliforme isolates from the midwestern United States, representing a south to north latitudinal gradient from Arkansas to Minnesota. Ten previously tested microsatellite loci were used to genotype isolates, and plant assays were conducted to assess virulence. Three distinct population clusters were differentiated across isolates. Although isolates ranged in virulence classes from low to very high, little correlation was found between virulence phenotype and cluster membership. Similarly, population structure and geographic location were not highly correlated. However, the earliest diverging cluster had the lowest genetic diversity and was detected only in southern states, whereas the two other clusters were distributed across the Midwest and were predominant in Minnesota. One of the midwestern clusters had the greatest genetic diversity and was found along the northern edge of the known distribution. The results support three genetically distinct population clusters of F. virguliforme in the United States, with two clusters contributing most to spread of this fungus across the Midwest.
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    A needle in a seedstack: an improved method for detection of rare alleles in bulk seed testing through KASP
    (Pest Management Science, 2021-02) Brusa, Anthony; Patterson, Eric L; Gaines, Todd A; Westra, Philip; Sparks, Crystal D; Wyse, Don; Dorn, Kevin
    BACKGROUND Amaranthus palmeri is an aggressive and prolific weed species with major impact on agricultural yield and is a prohibited noxious weed across the Midwest. Morphological identification of A. palmeri from other Amaranthus species is extremely difficult in seeds, which has led to genetic testing for seed identification in commercial seed lots. RESULTS We created an inexpensive and reliable genetic test based on novel, species‐specific, single nucleotide polymorphisms (SNPs) from GBS (Genotyping by Sequencing) data. We report three SNP‐based genetic tests for identifying A. palmeri alone or in a mixed pool of Amaranthus spp. Sensitivity ranged from 99.8 to 100%, specificity from 99.59 to 100%. Accuracy for all three tests is > 99.7%. All three are capable of reliably detecting one A. palmeri seed in a pool of 200 Amaranthus spp. seeds. The test was validated across 20 populations of A. palmeri, along with eight other Amaranthus species, the largest and most genetically diverse panel of Amaranthus samples to date. CONCLUSION Our work represents a marked improvement over existing commercial assays resulting in an identification assay that is (i) accurate, (ii) robust, (iii) easy to interpret and (iv) applicable to both leaf tissue and pools of up to 200 seeds. Included is a data transformation method for calling of closely grouped competitive fluorescence assays. We also present a comprehensive GBS dataset from the largest geographic panel of Amaranthus populations sequenced. Our approach serves as a model for developing markers for other difficult to identify species.
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    Two-Stage Batch Algorithm for Nonlinear Static Parameter Estimation
    (Journal of Guidance, Control, and Dynamics, 2020) Kerry, Sun; Gebre-Egziabher, Demoz
    A two-stage batch estimation algorithm for solving a class of nonlinear, static parameter estimation problems that appear in aerospace engineering applications is proposed. It is shown how these problems can be recast into a form suitable for the proposed two-stage estimation process. In the first stage, linear least squares is used to obtain a subset of the unknown parameters (set 1) and a residual sampling procedure is used for selecting initial values for the rest of the parameters (set 2). In the second stage, depending on the uniqueness of the local minimum, either only the parameters in the second set need to be re-estimated, or all the parameters will have to be re-estimated simultaneously, by a nonlinear constrained optimization. The estimates from the first stage are used as initial conditions for the second-stage optimizer. It is shown that this approach alleviates the sensitivity to initial conditions and minimizes the likelihood of converging to an incorrect local minimum of the nonlinear cost function. An error bound analysis is presented to show that the first stage can be solved in such a way that the total cost function will be driven to the optimal cost, and the difference has an upper bound. Two tutorial examples are used to show how to implement this estimator and compare its performance to other similar nonlinear estimators. Finally, the estimator is used on a 5-hole Pitot tube calibration problem using flight test data collected from a small unmanned aerial vehicle that cannot be easily solved with single-stage methods.