Target spot is a foliar disease of soybean that can produce yield losses. The disease has recently become a concern due to increasing intensity of its epidemics in the main soybean growing countries (USA, Brazil and Argentina). The goals of this study were to i) estimate the target spot control efficiency and yield response of labeled fungicides for the main soybean growing region of Brazil and identify factors affecting their performance; ii) characterize the relationship between target spot severity and soybean yield using meta-analytic techniques, and to identify patterns which allow understanding the heterogeneity in the relationship; iii) to explore the variability of genetic resistance of cultivars and verify the less time-consuming methodology for doing it; iv) explore the pathogen-host interaction effects on the epidemic development; v) compare the sensitiveness of the canopy strata position injured by C. cassiicola to reduce grain yield. Fungicides containing fluxapyroxad + pyraclostrobin were the most efficient ones to control target spot, with control levels of 75% and their yield response depended on the disease pressure (DP, DPLow < 35% target spot severity at untreated checks <= DPHigh). At DPLow was unprofitable the use of fungicides and at DPHigh the latter fungicides had the best performances increasing yield relative to the untreated check in > 469 kg ha-1 (+19.1%). Potential yield of soybean in absence of target spot was estimated in 3507 kg ha-1 for 41 trials in Brazil and the percentual reduction for each target spot severity point was calculated in 0.48%, what would represent a reduction of 24% in a hypothetical target spot severity of 50% (ranging from 8% to 42%). The soybean cultivar had a significant effect to explain this wide range of responses: potential losses of 11%, 18.5% and 42% was calculated for cultivar BMX Potência RR, TMG803 and M9144RR respectively at target spot severity = 50%. We observed high variability on the genetic resistance in the tested germplasm: cultivars with very low target spot intensity (BRS360) to highly susceptible cultivars. A single-point disease severity assessment was not as reliably as an integrative three-point assessment, which had no difference with a less time-consuming two-point disease assessment. In trials where 3 C.cassicola isolates from different regions of Brazil were inoculated individually on 3 soybean cultivars contrasting in their resistance level we observed that the incubation period, disease severity, lesion density and lesion size at 14 days after inoculation, were influenced by the cultivar and not by isolate geographical origin. Using disease severity coupled with defoliation assessments throughout the reproductive growth stages, we performed correlations between grain yield and the leaf area injury at different plant positions - growth stages. The best correlation was observed with the assessments at R5.5 for injuries at middle canopy section. / A mancha alvo é uma doença foliar que pode ocasionar perdas de rendimento na cultura da soja. A doença tornou-se recentemente uma preocupação nos principais países produtores de soja (EUA, Brasil e Argentina), devido à crescente intensidade de suas epidemias. Os objetivos deste estudo foram: i) estimar a eficiência de controle da mancha alvo por fungicidas comerciais registrados no Brasil e a resposta em rendimento da soja, identificando fatores que afetam o desempenho dos fungicidas; ii) caracterizar a relação entre a severidade da mancha alvo e o rendimento da soja, utilizando técnicas meta-analíticas e identificar padrões que permitam compreender a heterogeneidade existente nessa relação; iii) explorar a variabilidade da resistência genética de cultivares de soja e verificar a metodologia mais eficiente para discriminar cultivares suscetíveis de resistentes; iv) explorar os efeitos da interação entre a origem do isolado de C. cassiicola e a cultivar de soja no desenvolvimento da epidemia; v) comparar a sensibilidade da posição do estrato do dossel afetado por C. cassiicola na redução do rendimento de grãos. Fungicidas compostos pelos ingredientes ativos fluxapyroxad + piraclostrobina foram os mais eficientes para controlar a mancha alvo, com níveis de controle de até 75%, e sua resposta ao rendimento dependeu da pressão da doença (PD, PDbaixa < 35% de severidade da mancha alvo na testemunha não tratada <= PDalta). Na PDbaixa, a aplicação de fungicidas não foi lucrativa, e em PDalta os fungicidas compostos por fluxapyroxad + piraclostrobina apresentaram os melhores desempenhos, superando o rendimento em relação à testemunha em 469 kg ha-1 (+ 19,1%). O rendimento potencial geral da soja, na ausência da mancha alvo, foi estimado em 3507 kg ha-1 para 41 ensaios distribuídos no Brasil. A redução no rendimento para cada ponto percentual de incremento na severidade da mancha alvo foi calculada em 0,48%. Com isso, níveis (hipotéticos) de severidade de mancha alvo de 50% ocasionariam uma redução de rendimento de 24% (variando entre 8% a 42%). A cultivar de soja teve um efeito significativo para explicar esta grande amplitude de respostas: reduções potenciais (com 50% de severidade) de 11%, 18,5% e 42% foram calculadas, respectivamente, para as cultivares BMX Potência RR, TMG803 e M9144RR. Foi constatada alta variabilidade na resistência genética no germoplasma testado, desde cultivares com intensidade de mancha alvo muito baixa (BRS360) até cultivares altamente suscetíveis. Avaliações da severidade da doença em uma única data não foi tão confiável quanto a avaliação integrada de duas ou três datas. Em experimentos onde 3 isolados de diferentes regiões do Brasil foram inoculados isoladamente em 3 cultivares contrastantes nos níveis de resistência, observou-se que o período de incubação, a severidade da doença, a densidade de lesões e o tamanho das lesões aos 14 dias após a inoculação foram influenciados pela cultivar. Porém, não foi observado efeito da origem geográfica do isolado de C. cassiicola nos componentes monocíclicos avaliados. A severidade da doença em diferentes posições da planta, juntamente com as avaliações de desfolha ao longo dos estádios de crescimento reprodutivo da soja, foi correlacionada ao rendimento de grãos. A melhor correlação entre o rendimento de grãos e a intensidade da doença (severidade + desfolha) foi observada nas avaliações em R5.5 na seção média do dossel.

Target spot is a foliar disease of soybean that can produce yield losses. The disease has recently become a concern due to increasing intensity of its epidemics in the main soybean growing countries (USA, Brazil and Argentina). The goals of this study were to i) estimate the target spot control efficiency and yield response of labeled fungicides for the main soybean growing region of Brazil and identify factors affecting their performance; ii) characterize the relationship between target spot severity and soybean yield using meta-analytic techniques, and to identify patterns which allow understanding the heterogeneity in the relationship; iii) to explore the variability of genetic resistance of cultivars and verify the less time-consuming methodology for doing it; iv) explore the pathogen-host interaction effects on the epidemic development; v) compare the sensitiveness of the canopy strata position injured by C. cassiicola to reduce grain yield. Fungicides containing fluxapyroxad + pyraclostrobin were the most efficient ones to control target spot, with control levels of 75% and their yield response depended on the disease pressure (DP, DPLow < 35% target spot severity at untreated checks <= DPHigh). At DPLow was unprofitable the use of fungicides and at DPHigh the latter fungicides had the best performances increasing yield relative to the untreated check in > 469 kg ha-1 (+19.1%). Potential yield of soybean in absence of target spot was estimated in 3507 kg ha-1 for 41 trials in Brazil and the percentual reduction for each target spot severity point was calculated in 0.48%, what would represent a reduction of 24% in a hypothetical target spot severity of 50% (ranging from 8% to 42%). The soybean cultivar had a significant effect to explain this wide range of responses: potential losses of 11%, 18.5% and 42% was calculated for cultivar BMX Potência RR, TMG803 and M9144RR respectively at target spot severity = 50%. We observed high variability on the genetic resistance in the tested germplasm: cultivars with very low target spot intensity (BRS360) to highly susceptible cultivars. A single-point disease severity assessment was not as reliably as an integrative three-point assessment, which had no difference with a less time-consuming two-point disease assessment. In trials where 3 C.cassicola isolates from different regions of Brazil were inoculated individually on 3 soybean cultivars contrasting in their resistance level we observed that the incubation period, disease severity, lesion density and lesion size at 14 days after inoculation, were influenced by the cultivar and not by isolate geographical origin. Using disease severity coupled with defoliation assessments throughout the reproductive growth stages, we performed correlations between grain yield and the leaf area injury at different plant positions - growth stages. The best correlation was observed with the assessments at R5.5 for injuries at middle canopy section. / A mancha alvo é uma doença foliar que pode ocasionar perdas de rendimento na cultura da soja. A doença tornou-se recentemente uma preocupação nos principais países produtores de soja (EUA, Brasil e Argentina), devido à crescente intensidade de suas epidemias. Os objetivos deste estudo foram: i) estimar a eficiência de controle da mancha alvo por fungicidas comerciais registrados no Brasil e a resposta em rendimento da soja, identificando fatores que afetam o desempenho dos fungicidas; ii) caracterizar a relação entre a severidade da mancha alvo e o rendimento da soja, utilizando técnicas meta-analíticas e identificar padrões que permitam compreender a heterogeneidade existente nessa relação; iii) explorar a variabilidade da resistência genética de cultivares de soja e verificar a metodologia mais eficiente para discriminar cultivares suscetíveis de resistentes; iv) explorar os efeitos da interação entre a origem do isolado de C. cassiicola e a cultivar de soja no desenvolvimento da epidemia; v) comparar a sensibilidade da posição do estrato do dossel afetado por C. cassiicola na redução do rendimento de grãos. Fungicidas compostos pelos ingredientes ativos fluxapyroxad + piraclostrobina foram os mais eficientes para controlar a mancha alvo, com níveis de controle de até 75%, e sua resposta ao rendimento dependeu da pressão da doença (PD, PDbaixa < 35% de severidade da mancha alvo na testemunha não tratada <= PDalta). Na PDbaixa, a aplicação de fungicidas não foi lucrativa, e em PDalta os fungicidas compostos por fluxapyroxad + piraclostrobina apresentaram os melhores desempenhos, superando o rendimento em relação à testemunha em 469 kg ha-1 (+ 19,1%). O rendimento potencial geral da soja, na ausência da mancha alvo, foi estimado em 3507 kg ha-1 para 41 ensaios distribuídos no Brasil. A redução no rendimento para cada ponto percentual de incremento na severidade da mancha alvo foi calculada em 0,48%. Com isso, níveis (hipotéticos) de severidade de mancha alvo de 50% ocasionariam uma redução de rendimento de 24% (variando entre 8% a 42%). A cultivar de soja teve um efeito significativo para explicar esta grande amplitude de respostas: reduções potenciais (com 50% de severidade) de 11%, 18,5% e 42% foram calculadas, respectivamente, para as cultivares BMX Potência RR, TMG803 e M9144RR. Foi constatada alta variabilidade na resistência genética no germoplasma testado, desde cultivares com intensidade de mancha alvo muito baixa (BRS360) até cultivares altamente suscetíveis. Avaliações da severidade da doença em uma única data não foi tão confiável quanto a avaliação integrada de duas ou três datas. Em experimentos onde 3 isolados de diferentes regiões do Brasil foram inoculados isoladamente em 3 cultivares contrastantes nos níveis de resistência, observou-se que o período de incubação, a severidade da doença, a densidade de lesões e o tamanho das lesões aos 14 dias após a inoculação foram influenciados pela cultivar. Porém, não foi observado efeito da origem geográfica do isolado de C. cassiicola nos componentes monocíclicos avaliados. A severidade da doença em diferentes posições da planta, juntamente com as avaliações de desfolha ao longo dos estádios de crescimento reprodutivo da soja, foi correlacionada ao rendimento de grãos. A melhor correlação entre o rendimento de grãos e a intensidade da doença (severidade + desfolha) foi observada nas avaliações em R5.5 na seção média do dossel.

<p>  </p> <p>Sudden death syndrome (SDS) caused by <em>Fusarium virguliforme</em> is one of the top yield-reducing diseases of soybean. This disease results in a two-stage symptom development, root rot followed by foliar interveinal chlorosis and necrosis. Foliar symptoms typically appear late in the growing season [full pod to full seed (R4 to R6) reproductive growth stages]. Prior to foliar symptoms, a destructive technique is usually carried out to identify the root rot phase of SDS. This technique requires intensive crop scouting and an expert for accurate diagnosis. Therefore, a nondestructive technique is needed to diagnose SDS disease in the absence of visible foliar symptoms. Additionally, no soybean cultivar is completely resistant to SDS and no single method can completely manage this disease. So, an improved integrated approach is needed for SDS disease management. </p> <p>Foliar fungal diseases such as frogeye leaf spot (<em>Cercospora sojina</em> Hara), Septoria brown spot (<em>Septoria glycines</em> Hemmi), and Cercospora leaf blight (<em>Cercospora</em> spp.) are also economically important diseases of soybean. To limit the losses caused by these diseases, several management methods can be used including the application of foliar fungicide. However, due to the low foliar disease pressure that is observed most years, fungicide applications may not be warranted to be applied annually in Indiana. </p> <p>The objectives of this research were: 1) to assess the effectiveness and economic impact of integrated management strategies that include cultivar selection, seed treatment, and seeding rate on SDS in Indiana; 2) to pre-symptomatically and non-destructively detect SDS disease using hyperspectral measurements; and 3) to evaluate foliar fungicides on soybean foliar diseases and yield in Indiana. </p> <p>Results from this research support the use of a seed treatment to protect soybean roots from SDS infection and the use of a moderately resistant cultivar planted at a seeding rate of 346,535 seeds/ha to protect yield and maximize on net returns. This research also demonstrated the ability of hyperspectral reflectance to discriminate healthy from <em>F. virguliforme</em> infected soybean roots in the absence of foliar symptoms. In addition, results show that fungicide applications can reduce foliar disease over the nontreated control, but under low foliar disease risk, these fungicides did not significantly increase yield over the nontreated control. Altogether, these results will contribute to improved soybean disease management approaches in Indiana.</p>

Botrytis bunch rot, caused by Botrytis cinerea, is a fungal disease that primarily affects the fruit of wine grapes. Infection of fruit consequently results in reduced yields and wine quality. These factors lead to significant economic losses for growers which prompts the implementation of management practices to control the disease. One objective of this study was to evaluate the level of resistance that populations of B. cinerea in the Central Coast region showed to various chemicals. A fungicide assay was conducted to determine resistant phenotypes to six fungicide active ingredients (pyrimethanil, iprodione, fenhexamid, fludioxonil, trifloxystrobin, boscalid). Thirty-five (2020) and 88 (2021) B. cinerea isolates were collected from Santa Maria, Cambria, Paso Robles, and Edna Valley in California and screened for resistance. The frequencies of populations (2020, 2021) showing resistance to each active ingredient were: pyrimethanil (94.3%, 81.8%), trifloxystrobin (97.1%, 100%), boscalid (77.1%, 77.3%), fenhexamid (8.6%, 25%). The majority of isolates were sensitive to iprodione (100%, 100%), fludioxonil (100%, 100%), fenhexamid (88.6%, 75%), and boscalid (22.9%, 22.7%). These results documented the accumulation of resistance in B. cinerea to various fungicides commonly used for Botrytis bunch rot management in California’s Central Coast. Another objective of this study was to determine the effective concentration of the six fungicides that reduces mycelial growth of the fungus by 50% (EC50). Seven B. cinerea isolates in 2020 and ten isolates in 2021 were selected and subjected to a sensitivity screening with serial dilutions of the different fungicide active ingredients. The fungicides found to have the highest EC50 values indicating reduced efficacy for inhibiting B. cinerea growth were Scala® (FRAC 9), Flint® (FRAC 11), and Endura® (FRAC 7). The fungicides found to have the lowest EC50 values indicating higher efficacy for inhibiting B. cinerea growth were Scholar® (FRAC 12) and Rovral® (FRAC 2). The results from this study provided information regarding the accumulated resistance of B. cinerea populations to certain chemical groups and therefore the efficacy of different fungicide active ingredients. This information can be utilized by growers as a tool to enhance and develop fungicide spray programs that effectively manage Botrytis bunch rot in Central Coast vineyards.

<p>  </p> <p>Tar spot is a new foliar disease of corn in the United States. Tar spot was first detected in 2015 and is now among the most important corn diseases in the Midwest. Tar spot is caused by the obligate biotrophic fungus, <em>Phyllachora maydis</em> Maubl, from the genus, <em>Phyllachora </em>which consist of over 1,200 species of host-specific fungi. Due to the recent emergence, studies relating to <em>P. maydis</em> population dynamics in the U.S. are limited. How much genetic diversity, variation, and level of gene flow are occurring within and among these populations? Knowledge of the population dynamics is imperative for understanding the pathogen’s biology, ecology, epidemiology, and management. Currently, no corn hybrid is fully resistant to tar spot. Foliar fungicides are currently the most effective option for disease management, but best practices for fungicide management remain unknown. Better information is needed on fungicide efficacy and fungicide application timing to reduce tar spot severity, protect yield, and increase profitability for Indiana corn growers. </p> <p>This research dissertation presents four chapters to answers those questions and bridge the gaps between the knowns and unknows of this novel corn-<em>Phyllachora maydis</em> pathosystem. <strong>Chapter 1</strong> presents a literature review on tar spot of corn, its economic impact, the causal pathogen, its host, lifecycle, distribution, and known management strategies as a resource for understanding the pathosystem in the U.S. <strong>Chapter 2</strong> examines the genetic population structure, diversity, geneflow and mode of reproduction in Midwest U.S. by employing microsatellite (SSR) markers. <strong>Chapter 3</strong> presents results from multi-year, multi-location, small-plot field trials on the net return of foliar fungicides and fungicide timing on tar spot management in Indiana. Lastly, <strong>Chapter 4</strong> concludes by evaluating of an integrated management strategy for tar spot by examining the integration of tillage, corn hybrids and fungicide application in reducing tar spot severity while protecting yields.</p> <p>Results provided in this research dissertation will be used to guide future studies and provide stakeholders such as researchers, corn growers, extension personnel in academia and industry with valuable information needed to guide effective disease management decisions. </p>

<p>The management of gray mold, caused by the fungus <em>Botrytis cinerea</em>, on ornamental plants relies heavily on fungicide applications. To improve fungicide efficacy, the manipulation of nozzle type, spray volume, and pressure influence droplet size (µm) and density (droplets/cm2) on the leaf’s surface. However, leaf wettability dictates how well the application droplets adhere and spread across the surface. When leaf surfaces are waxy (hydrophobic) or hairy (tomentose), droplets fail to adhere, impacting fungicide sorption.</p> <p>The goal of this research was to evaluate how the interaction of droplet density and leaf wettability impact the efficacy of chemical and biological fungicides against <em>Botrytis cinerea</em>. Leaf surfaces vary between species, within species, leaf age, and leaf sides (abaxial or adaxial). Hydrophobic leaf surfaces influence fungicide efficacy by reducing fungicide droplet spread compared to the wettable and hydrophilic leaf surfaces. The presence of trichomes on the leaf surface can inhibit droplets from reaching the surface.</p> <p>To quantify droplet density, a fine and coarse spray of fungicide treatments was applied with a yellow fluorescent dye. After application, <em>Begonia</em> x <em>hybrida</em> ‘Dragon wing’ leaves were placed on black, blackout curtains below a blacklight. Images were analyzed by ImageJ, using an image processing method. The number of lesions, disease incidence, were counted to observe fungicide efficacy. Results show there was no interaction between the actual droplet density within treatments applied with fine and coarse sprays. However, the interaction between spray type (fine and coarse) and treatments can have a significant effect on disease incidence. Disease incidence was significantly different between the systemic and contact fungicides for fine and coarse sprays. However, the systemic fungicide treatment had the highest disease incidence compared to the contact fungicide.</p> <p>To assess leaf wettability impact on fungicide efficacy, five <em>Begonia </em>species (<em>B. scharffii, B. erythrophylla, B. </em>x<em> hybrida ‘</em>Dragon Wing’<em>, B. epipsila, and B. goldingiana</em>) were used based on their observed leaf surface type. A contact angle goniometer was used to take pictures of a droplet on <em>Begonia</em> leaf surfaces. The quantification of the leaf surface took place by using the ImageJ program ‘Drop-Snake’ within the plugin ‘Drop Analysis’. The number of lesions, an indicator of disease incidence, were counted to observe fungicide efficacy. Results showed the contact angles were different between the <em>Begonia</em> species. There was a significant interaction between the <em>Begonia</em> species and treatments, where <em>Begonia</em> ‘hairy’ and ‘waxy’ leaf surfaces can influence fungicide efficacy. However, there was no significance for the interaction between <em>Begonia</em> species’ contact angles and treatments.</p> <p>These studies advance our understanding of how droplet density and leaf surfaces influence fungicide efficacy, thus improving our ability to manage <em>Botrytis</em> for diverse ornamental plants. </p>