How the Global Burden of Animal Diseases links to the Global Burden of Crop Loss: a food systems perspective.

Food systems comprise interconnected webs of processes that together transform inputs (land, labour, water, nutrients and genetics, to mention just a few) into outputs such as nutrition and revenue for human societies. Perfect systems do not exist; rather, global food systems operate in the presence of hazards, biotic and abiotic alike, and under the constraint of limited resources to mitigate these hazards. There are, therefore, inefficiencies in these systems, which lead to losses in terms of monetary, nutritional, health and environmental values and create additional negative externalities in the health, social and environmental spaces. Health hazards in the food system do not respect arbitrary distinctions between the crop and livestock sectors, which are highly interconnected. These linkages exist where one sector provides inputs to another or through substitution effects where supply in one sector influences demand in another. The One Health approach advocates investigating the intersectoral hazards in a highly interdisciplinary manner. This article provides a conceptual framework for integrating the methodologies developed by the Global Burden of Crop Loss and Global Burden of Animal Diseases initiatives to generate burden estimates for hazards in food systems that better account for interconnectivity and foster an improved understanding of food systems that is aligned with the interdisciplinary nature of the One Health approach. A case study related to maize and poultry sector linkages in the wider context of public and environmental health is presented.

Les systèmes alimentaires sont des réseaux de processus interconnectés qui concourent à transformer des intrants (terre, main-d'oeuvre, eau, nutriments et génétique, pour n'en mentionner que quelques-uns) en extrants tels que des aliments et des revenus pour les sociétés humaines. Il n'existe pas de système parfait ; les systèmes alimentaires mondiaux sont exposés en permanence à des dangers de nature tant biotique qu'abiotique et contraints par les ressources limitées consacrées à l'atténuation de ces dangers. Les problèmes d'efficacité sont donc inéluctables ; ils entraînent des pertes de valeur tant monétaire que nutritionnelle, sanitaire et environnementale, et génèrent de nouvelles externalités négatives dans le domaine de la santé ainsi que dans l'espace social et dans l'environnement. Les dangers sanitaires présents dans le système alimentaire ignorent les distinctions arbitraires entre les secteurs agricole et d'élevage, lesquels sont fortement interconnectés. Ces liens se manifestent lorsqu'un secteur fournit des intrants à l'autre et, par l'effet de substitutions, lorsque l'offre dans un secteur influence la demande dans l'autre. L'approche " Une seule santé " préconise d'adopter une méthode fondée sur l'interdisciplinarité pour enquêter sur les dangers intersectoriels. Les auteurs décrivent le cadre conceptuel de l'intégration des méthodes des initiatives " Fardeau mondial des pertes agricoles " et " Impact mondial des maladies animales " dans le but de produire des estimations de la charge induite par les dangers des systèmes alimentaires qui prennent davantage en compte leur inter-connectivité et donnent lieu à une meilleure compréhension des systèmes alimentaires, en cohérence avec le caractère interdisciplinaire de l'approche " Une seule santé ". Est également présentée une étude de cas portant sur les liens entre la culture du maïs et l'élevage de volailles dans le contexte plus large de la santé publique et environnementale.

Los sistemas alimentarios comprenden redes interconectadas de procesos que, conjuntamente, transforman insumos (tierra, mano de obra, agua, nutrientes y genética, por mencionar solo algunos) en productos como alimentos e ingresos para las sociedades humanas. No existen sistemas perfectos; más bien, los sistemas alimentarios mundiales funcionan en un entorno de peligros, tanto bióticos como abióticos, y con las restricciones impuestas por los limitados recursos disponibles para mitigarlos. En estos sistemas se observan, por tanto, ineficiencias, que provocan pérdidas en términos monetarios, nutricionales, sanitarios y ambientales y que crean externalidades negativas adicionales en los ámbitos sanitario, social y ambiental. Los peligros para la salud en los sistemas alimentarios no atienden a distinciones arbitrarias entre los sectores agrícola y ganadero, que están muy interconectados. Estos vínculos surgen cuando un sector proporciona insumos a otro o a través de efectos de sustitución en los que la oferta de un sector influye en la demanda de otro. El enfoque de "Una sola salud" aboga por investigar los peligros intersectoriales de manera eminentemente interdisciplinaria. En este artículo se ofrece un marco teórico para la integración de las metodologías desarrolladas por las iniciativas dedicadas al impacto global de las pérdidas de cosechas y al impacto global de las enfermedades animales a fin de obtener estimaciones de los peligros en los sistemas alimentarios que tengan más en cuenta la interconexión y fomenten una mejor comprensión de los sistemas alimentarios acorde con el carácter interdisciplinario del enfoque de "Una sola salud". En este sentido, se presenta un estudio de caso relacionado con los vínculos entre los sectores del maíz y las aves de corral en el contexto más amplio de la salud pública y ambiental.

Fifty Years of Fungicide Development, Deployment, and Future Use.

Plant disease management has not significantly changed in the past 50 years, even as great strides have been made in the understanding of fungal biology and the etiology of plant disease. Issues of climate change, supply chain failures, war, political instability, and exotic invasives have created even more serious implications for world food and fiber security, and the stability of managed ecosystems, underscoring the urgency for reducing plant disease-related losses. Fungicides serve as the primary example of successful, widespread technology transfer, playing a central role in crop protection, reducing losses to both yield and postharvest spoilage. The crop protection industry has continued to improve upon previous fungicide chemistries, replacing active ingredients lost to resistance and newly understood environmental and human health risks, under an increasingly stricter regulatory environment. Despite decades of advances, plant disease management continues to be a constant challenge that will require an integrated approach, and fungicides will continue to be an essential part of this effort.

Relative Contribution of Windbreak, Copper Sprays, and Leafminer Control for Citrus Canker Management and Prevention of Crop Loss in Sweet Orange Trees.

The management of citrus canker, caused by Xanthomonas citri subsp. citri, has been widely studied in endemic areas because of the importance of the disease in several citrus-producing countries. A set of control measures is well established, but no study has investigated the efficiency of each measure individually and their combination for disease suppression. This study comprised a 3-year field study to assess the relative contribution of three measures for the control of citrus canker and reduction of crop losses. Windbreak (Wb), copper sprays (Cu), and leafminer control (Lc) were assessed in eight different combinations in a split-split plot design. The orchard was composed of 'Valencia' sweet orange trees grafted onto 'Rangpur' lime. Casuarina cunninghamiana trees were used as Wb. Cu and Lc sprays were performed every 21 days throughout the year. Individually, Cu showed the highest contribution for canker control, followed by Wb. Lc had no effect on reducing citrus canker. Wb+Cu showed the highest efficiency for control of the disease. This combination reduced the incidence of diseased trees by approximately 60%, and the incidence of diseased leaves and fruit by ≥90% and increased the yield in 2.0- to 2.6-fold in comparison with the unmanaged plots. Cu sprays were important for reducing disease incidence and crop losses, whereas Wb had an additional contribution in minimizing the incidence of cankered, non-marketable fruit. The results indicated that the adoption of these measures of control may depend on the characteristics of the orchard and destination of the production.

Using Panel Community Surveys to Track the Impact of Crop Pests Over Time and Space - The Case of Maize Lethal Necrosis (MLN) Disease in Kenya from 2013 to 2018.

Maize lethal necrosis (MLN) disease appeared in Kenya in 2011, causing major damage. In a first survey of 121 communities in 2013, participants estimated the proportion of households affected and the yield loss in affected areas; from this survey, the overall loss was estimated at 22%, concentrated in western Kenya (94%). Efforts to combat the disease included planting resistant varieties, creating awareness of MLN management, and producing pathogen-free seed. In 2018, the same communities were revisited and asked the same questions, establishing a panel community survey. The results showed that incidents of MLN had greatly decreased, and the number of communities that had observed it had reduced from 76% in 2013 to 26% by the long rains of 2018; while still common in western Kenya (60%), MLN had greatly reduced elsewhere (to 10%). In 2013, 40% of farmers were affected, yield loss among affected farmers was estimated at 44%, and total yield loss was estimated at 22% (a production loss of 0.5 million metric tons/year), valued at US$187 million. By the long rains of 2018, 23% of farmers were affected, with a loss among affected farmers of 36%; overall annual loss was estimated at 8.5% or 0.37 million metric tons, valued at US$109 million, concentrated in western Kenya (79%). Of the recommended control measures, only the removal of diseased plants was commonly used (by 62% of affected communities), but not the use of agronomic practices (11%) or resistant varieties (9.5%). The reasons for the reduction in MLN are not well understood; external factors such as spraying insecticide against fall armyworm and unfavorable weather likely played a role, as did using disease-free seed, but not the use of resistant varieties or appropriate management practices. Still, as the pathogen remains in the fields, it is important to keep disseminating these control methods, particularly resistant varieties.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Smartphone Application-Enabled Apple Fruit Surface Temperature Monitoring Tool for In-Field and Real-Time Sunburn Susceptibility Prediction.

Heat stress and resulting sunburn is a major abiotic stress in perineal specialty crops. For example, such stress to the maturing fruits on apple tree canopies can cause several physiological disorders that result in considerable crop losses and reduced marketability of the produce. Thus, there is a critical technological need to effectively monitor the abiotic stress under field conditions for timely actuation of remedial measures. Fruit surface temperature (FST) is one of the stress indicators that can reliably be used to predict apple fruit sunburn susceptibility. This study was therefore focused on development and in-field testing of a mobile FST monitoring tool that can be used for real-time crop stress monitoring. The tool integrates a smartphone connected thermal-Red-Green-Blue (RGB) imaging sensor and a custom developed application ('AppSense 1.0') for apple fruit sunburn prediction. This tool is configured to acquire and analyze imagery data onboard the smartphone to estimate FST. The tool also utilizes geolocation-specific weather data to estimate weather-based FST using an energy balance modeling approach. The 'AppSense 1.0' application, developed to work in the Android operating system, allows visual display, annotation and real-time sharing of the imagery, weather data and pertinent FST estimates. The developed tool was evaluated in orchard conditions during the 2019 crop production season on the Gala, Fuji, Red delicious and Honeycrisp apple cultivars. Overall, results showed no significant difference (t110 = 0.51, p = 0.6) between the mobile FST monitoring tool outputs, and ground truth FST data collected using a thermal probe which had accuracy of ±0.4 °C. Upon further refinements, such tool could aid growers in real-time apple fruit sunburn susceptibility prediction and assist in more effective actuation of apple fruit sunburn preventative measures. This tool also has the potential to be customized for in-field monitoring of the heat stressors in some of the sun-exposed perennial and annual specialty crops at produce maturation.

Comparative bioefficacy of Bacillus and Pseudomonas chitinase against Helopeltis theivora in tea (Camellia sinensis (L.) O.Kuntze.

Tea (Camellia sinensis (L.) O.Kuntze) is an industry-oriented economical crop in India. Among the sap sucking pests, tea mosquito bug (Helopeltis theivora) is one of the most serious pests causing heavy crop loss in tea plantation. Continuous use of chemical pesticides causes environmental pollution and health hazards besides developing pesticide residues in tea powder. The control of pests by bacterial metabolite is an alternative that may contribute to reduce or eliminate the chemical pesticide use. The use of chitinase as a biological control is an emerging field of research. In the present study, Chitinase (~ 25 kDa) was purified from Bacillus cereus C-13 strain using gel-filtration chromatography and further characterized for its optimum pH, temperature and substrate specificity. Bioefficacy of chitinase from B. cereus C-13 was compared with our previously reported Pseudomonas fluorescens MP-13 chitinase against H. theivora. Result concluded that, 100% and 78% mortality was observed by using P. fluorescens MP-13 chitinase and B. cereus C-13 chitinase, respectively. In future, bacterial chitinase can be utilized in eco-friendly pest management strategies.

Solar array placement, electricity generation, and cropland displacement across California's Central Valley.

Understanding agriculturally co-located solar photovoltaic (PV) installation capacity, practices, and preferences is imperative to foster a future where solar power and agriculture co-exist with limited impacts on food production. Crops and PV panels are often co-located as they have similar ideal conditions for maximum yield. The recent boom in solar photovoltaics is displacing a significant amount of cropland. The literature on agriculturally co-located PV array installations lacks important spatiotemporal details that could help inform future array installations and improve associated policies and incentive programs. This study used imagery from the National Agriculture Imagery Program for object-based analysis (within eCognition Developer), and from Landsat 5 TM, 7 ETM+ and 8 OLI for temporal analysis (using LandTrendr) to identify and characterize non-residential ground-mounted PV arrays in California's Central Valley installed between 2008 and 2018. This dataset includes over 210,000 individually identified panels grouped by mount and installation year into 1006 PV arrays (69% are agriculturally co-located). The most common type of mounting system is fixed-axis, and individual co-located systems tend to be small (0.34 MW). There were fewer single-axis tracking arrays, although the average capacity per system is nearly four times higher (1.20 MW). In total, the mapped arrays accounted for 3.6 GW of capacity and generated a cumulative of 32,700 GWh within the Central Valley during the study period. For the 694 identified agriculturally co-located arrays (2.1 GW), significantly sub-optimal installation practices were observed in the spacing and spatial field placement of the arrays. In terms of crop conversion preferences, commodity crops (pastureland) dominated the total cumulative area converted although specialty crops (orchards) also contributed to a large number of solar installations on cropland. These results provide important details of current PV placement practices; understanding these can help to inform future practices and guide future regulations that might promote solar installations while preserving agricultural production.

Climate-Fungal Pathogen Modeling Predicts Loss of Up to One-Third of Tea Growing Areas.

Climate change will affect numerous crops in the future; however, perennial crops, such as tea, are particularly vulnerable. Climate change will also strongly influence fungal pathogens. Here, we predict how future climatic conditions will impact tea and its associated pathogens. We collected data on the three most important fungal pathogens of tea (Colletotrichum acutatum, Co. camelliae, and Exobasidium vexans) and then modeled distributions of tea and these fungal pathogens using current and projected climates. The models show that baseline tea-growing areas will become unsuitable for Camellia sinensis var. sinensis (15 to 32% loss) and C. sinensis var. assamica (32 to 34% loss) by 2050. Although new areas will become more suitable for tea cultivation, existing and potentially new fungal pathogens will present challenges in these areas, and they are already under other land-use regimes. In addition, future climatic scenarios suitable range of fungal species and tea suitable cultivation (respectively in CSS and CSA) growing areas are Co. acutatum (44.30%; 31.05%), Co. camelliae (13.10%; 10.70%), and E. vexans (10.20%; 11.90%). Protecting global tea cultivation requires innovative approaches that consider fungal genomics as part and parcel of plant pathology.

The Economic Impacts and Management of Spotted Wing Drosophila (Drosophila Suzukii): The Case of Wild Blueberries in Maine.

Drosophila suzukii (Matsumura), or spotted wing drosophila, has become a major pest concern for berry growers in the United States. In this study, we evaluated the economic impacts of D. suzukii on the Maine wild blueberry industry from two perspectives. The first analysis estimated the state-level economic impacts of D. suzukii on the wild blueberry industry in Maine in the absence of control. We found that D. suzukii could result in drastic revenue losses to the industry, which could be over $6.8 million under the worst-case scenario (assuming a 30% yield reduction). In the second analysis, we used Monte Carlo simulation to compare the expected revenues under different management strategies for a typical wild blueberry farm in Maine. The analysis focused on a decision-making week during the harvesting season, which the grower can choose in between three control strategies: no-control, early harvest, or insecticide application. The results suggested that insecticide applications are not economically optimal in most low infestation risk scenarios. Furthermore, although the early harvest strategy is one of the strategies to avoid D. suzukii infestations for wild blueberry production in Maine, the tradeoff is the revenue loss from the unripe crop. Using the simulation results, we summarized optimal harvest timing regarding the fruit maturity level under different D. suzukii infestation risk scenarios, which can minimize the revenue loss from adopting the early harvest management strategy.

Modeling the Impact of Crop Diseases on Global Food Security.

Plant pathology must contribute to improving food security in a safe operating space, which is shrinking as a result of declining natural resources, climate change, and the growing world population. This review analyzes the position of plant pathology in a nexus of relationships, which is mapped and where the coupled dynamics of crop growth, disease, and yield losses are modeled. We derive a hierarchy of pathogens, whereby pathogens reducing radiation interception (RI), radiation use efficiency (RUE), and harvest index increasingly impact crop yields in the approximate proportions: 1:4.5:4,700. Since the dawn of agriculture, plant breeding has targeted the harvest index as a main objective for domesticated plants. Surprisingly, the literature suggests that pathogens that reduce yields by directly damaging harvestable plant tissues have received much less attention than those that reduce RI or RUE. Ecological disease management needs to target diverse production situations and therefore must consider variation in attainable yields; this can be achieved through the reengineering of agrosystems to incorporate built-in dynamic diversity of genes, plants, and crop stands.

Modeling the effects of precipitation and temperature patterns on agricultural drought in China from 1949 to 2015.

Agricultural drought is one of the most frequent and widespread natural disasters occurring in China. Drought is associated with hydrological and meteorological conditions that lead to water-deficient vegetation, which has a negative effect on agricultural activities. The monitoring of droughts, as well as early-warning and timely information, is significant for crop production and food security. However, the spatial and temporal patterns of precipitation and temperature have rarely been reported when monitoring the agricultural drought loss rate on a national scale. In this study, we analyzed the spatial and temporal patterns of drought based on model simulation. An artificial neural network (ANN) model for drought warning was developed using monthly temperature and precipitation data from 1949 to 2015. Our results demonstrated that the agricultural drought loss rate can be simulated in most agricultural areas of China. Our ANN model simulation revealed that the areal percentages of precipitation and temperature are strongly correlated with agricultural drought, with the agricultural drought loss rate exhibiting greater sensitivity to precipitation than temperature. We suggest that the spatial and temporal patterns of precipitation are useful for capturing drought warning signals. The precipitation thresholds play an important role in detecting agricultural drought in critical months or seasons of crop growth in different regions. This study presents a framework and reference for drought monitoring in the regions and countries facing frequent agricultural drought.

Loss of crop yields in India due to surface ozone: an estimation based on a network of observations.

Surface ozone is mainly produced by photochemical reactions involving various anthropogenic pollutants, whose emissions are increasing rapidly in India due to fast-growing anthropogenic activities. This study estimates the losses of wheat and rice crop yields using surface ozone observations from a group of 17 sites, for the first time, covering different parts of India. We used the mean ozone for 7 h during the day (M7) and accumulated ozone over a threshold of 40 ppbv (AOT40) metrics for the calculation of crop losses for the northern, eastern, western and southern regions of India. Our estimates show the highest annual loss of wheat (about 9 million ton) in the northern India, one of the most polluted regions in India, and that of rice (about 2.6 million ton) in the eastern region. The total all India annual loss of 4.0-14.2 million ton (4.2-15.0%) for wheat and 0.3-6.7 million ton (0.3-6.3%) for rice are estimated. The results show lower crop loss for rice than that of wheat mainly due to lower surface ozone levels during the cropping season after the Indian summer monsoon. These estimates based on a network of observation sites show lower losses than earlier estimates based on limited observations and much lower losses compared to global model estimates. However, these losses are slightly higher compared to a regional model estimate. Further, the results show large differences in the loss rates of both the two crops using the M7 and AOT40 metrics. This study also confirms that AOT40 cannot be fit with a linear relation over the Indian region and suggests for the need of new metrics that are based on factors suitable for this region.

Plant Diseases and Management Approaches in Organic Farming Systems.

Organic agriculture has expanded worldwide. Numerous papers were published in the past 20 years comparing plant diseases in organic and conventional crops. Root diseases are generally less severe owing to greater soil health, whereas some foliar diseases can be problematic in organic agriculture. The soil microbial community and nitrogen availability play an important role in disease development and yield. Recently, the focus has shifted to optimizing organic crop production by improving plant nutrition, weed control, and plant health. Crop-loss assessment relating productivity to all yield-forming and -reducing factors would benefit organic production and sustainability evaluation.

Pratylenchus thornei Associated with Reduced Wheat Yield in Oregon.

Pratylenchus thornei reaches high population densities in non-irrigated annual cropping systems in low-rainfall regions of the Pacific Northwest. Two spring wheat varieties with different levels of tolerance and susceptibility to P. thornei were treated or not treated with aldicarb in three experiments. Grain yield was inversely correlated (P < 0.05) with pre-plant populations of P. thornei in soil and with P. thornei density in mature roots. As population of P. thornei increased, yield of the moderately tolerant/moderately susceptible variety Krichauff was generally more stable than for the intolerant/susceptible variety Machete. The reproductive factor (Pf/Pi) was generally lower (P < 0.05) for Krichauff than Machete. Aldicarb improved wheat yield (P < 0.05) in highly infested fields by an average of 67% for Krichauff and 113% for Machete. Aldicarb increased (P < 0.05) numbers of headed tillers, plant height, and grain test weight and kernel weight, and reduced (P < 0.05) the density of P. thornei in mature wheat roots, variability in height of heads, and leaf canopy temperature. Aldicarb did not improve yield in a soil with a low population of P. thornei. This is the first report that P. thornei causes economic damage to wheat in the Pacific Northwest.

Salicylic acid-induced abiotic stress tolerance and underlying mechanisms in plants.

Abiotic stresses (such as metals/metalloids, salinity, ozone, UV-B radiation, extreme temperatures, and drought) are among the most challenging threats to agricultural system and economic yield of crop plants. These stresses (in isolation and/or combination) induce numerous adverse effects in plants, impair biochemical/physiological and molecular processes, and eventually cause severe reductions in plant growth, development and overall productivity. Phytohormones have been recognized as a strong tool for sustainably alleviating adverse effects of abiotic stresses in crop plants. In particular, the significance of salicylic acid (SA) has been increasingly recognized in improved plant abiotic stress-tolerance via SA-mediated control of major plant-metabolic processes. However, the basic biochemical/physiological and molecular mechanisms that potentially underpin SA-induced plant-tolerance to major abiotic stresses remain least discussed. Based on recent reports, this paper: (a) overviews historical background and biosynthesis of SA under both optimal and stressful environments in plants; (b) critically appraises the role of SA in plants exposed to major abiotic stresses;

Effect of Barley yellow dwarf virus Infection on Yield and Malting Quality of Barley.

Barley yellow dwarf virus (BYDV) infection occurs frequently in barley in the Upper Midwest region of the United States; however, the impact of this disease on the yield and quality of malting cultivars has not been adequately addressed. Studies were conducted at Fargo, North Dakota (from 1989 to 1990) to determine the effect of BYDV infection on yield and malt quality parameters in barley. Three malting cultivars varying in yield potential and malting characteristics were artificially inoculated at the seedling stage with a North Dakota BYDV isolate of the PAV serotype. Overall yields were reduced 32.5 to 38% in 1989 and 8.5 to 19.8% in 1990 by BYDV infection. Thousand-kernel weight (3.2 to 14.9%) and kernel plumpness (11.9 to 38.9%) also were reduced. Kernel color and three malt quality parameters (α-amylase, malt recovery, and wort viscosity) were not affected by BYDV infection. Increases in wort protein (2.5 to 14.5%) and diastatic power (3.8 to 12.6%), and decreases in malt extract (1.1 to 5.6%) were found. Most notably, total protein increased 4.6 to 17.5% with BYDV infection. Higher proportions of thin seed, as a result of BYDV infection, contributed to the effects on several quality parameters. In summary, the negative effect of BYDV infection on overall quality is significant and should be considered when assessing the impact of this disease. Although annual BYD disease-related losses are typically not extensive in the Midwestern malting barley region, the incorporation of host resistance into recommended cultivars would ameliorate the negative effects of BYD disease on crop quality as well as on yield.

Estimating Yield and Economic Loss from Constriction Canker of Peach.

Constriction cankers, caused by Phomopsis amygdali, girdle and kill fruiting twigs which results in a direct crop loss. To quantitatively determine this loss from 1996 to 1998, the number of fruit lost per infected shoot was estimated as a function of disease incidence in 21 severely infected orchards in New Jersey. For each cultivar in 1997 and 1998, the distribution of fruit sizes at harvest and prices at shipping were used to calculate total crop value for typical expected yields. Economic loss was then calculated from yield loss and crop value estimates. The overall percent yield loss mean across all sites and cultivars, unadjusted for fruit remaining on infected shoots, was 22.2, 30.7, and 23.7% for 1996, 1997, and 1998, respectively. The frequency of these losses were not normally distributed, and the nonparametric Friedman test indicated that yield loss was significantly different among years. Assuming the remaining fruit on infected shoots were harvested, yield losses for 1997 and 1998 were 28.5 and 21.0%, which translated into average economic losses of $4,009 and 2,803/ha, respectively, for an expected yield level of 14,010 kg/ha. These loss values justify control measures for management of constriction canker in severely infected orchards.

Quantifying Alfalfa Yield Losses Caused by Foliar Diseases in Iowa, Ohio, Wisconsin, and Vermont.

Although foliar diseases of alfalfa occur throughout the United States wherever alfalfa is grown, little work has been done to quantify yield losses caused by foliar pathogens since the late 1980s. To quantify the yield losses caused by foliar diseases of alfalfa, field experiments were performed in Iowa, Ohio, Vermont, and Wisconsin from 1995 to 1998. Different fungicides and fungicide application frequencies were used to obtain different levels of foliar disease in alfalfa. Visual disease and remote sensing assessments were performed weekly to determine the relationships between disease assessments and alfalfa yield. Visual disease assessments of percentage of defoliation, disease incidence, and disease severity were performed weekly, approximately five to six times during each alfalfa growth cycle. Remote sensing assessments also were obtained weekly by measuring the percentage of sunlight reflected from alfalfa canopies using handheld, multispectral radiometers. Yield loss estimates were calculated as the yield difference between the fungicide treatment with the highest yield and the nonfungicide control, divided by the yield obtained from the highest yielding fungicide treatment × 100. Over the 4-year period, significant alfalfa yield losses (P ≤ 0.05) occurred on 22 of the 48 harvest dates for the four states. The average significant yield loss for the 22 harvests was 19.3%. Both visual and percentage of reflectance assessments were used as independent variables in linear regression models to quantify the relationships between assessments and alfalfa yield. From 1995 to 1998, visual disease assessments were performed for a total of 209 dates and remote sensing assessments were performed on 198 dates from the four states. Yield models were developed for each of these assessment dates. There were 26/209, 26/209, and 17/209 significant yield models based on percentage of defoliation, disease incidence, and disease severity, respectively. Most of the significant models were for disease assessments performed on or within 1 or 2 weeks of the date of alfalfa harvest. When the significant models were averaged, percentage of defoliation, disease incidence, and disease severity explained 51, 55, and 52% of the variation in alfalfa yield, respectively. There were a total of 68/198 significant alfalfa yield models based on remote sensing assessments, and the significant models (averaged) explained 62% of the variation in alfalfa yield. Alfalfa foliar diseases continue to have a significant negative impact on alfalfa yields in the United States and remote sensing appears to offer a better means to quantify the impact of foliar diseases on alfalfa yield compared with visual assessment methods.

Effect of Within-field Variation in Soil Texture on Heterodera glycines and Soybean Yield.

The influence of soil texture on Soybean yield in the presence of Heterodera glycines was investigated by comparing yields of susceptible cultivars with a resistant cultivar for 2 years. Soybean yield was negatively correlated with increasing sand content (P = 0.05). Yields of susceptible cultivars were suppressed with increasing sand content. Final nematode population densities were lowest in plots with greatest sand content. Soybean infection by SCN, as determined by the number of cysts 30 days after planting, was not consistently related to soil texture over 2 years. Initial nematode population density was positively related to soybean yield the first year and negatively related to soybean yield the second, probably a result of greater yield suppression by H. glycines in plots with greater sand content.

Overestimation of Yield Loss of Tobacco Caused by the Aggregated Spatial Pattern of Meloidogyne incognita.

Overestimation of yield loss caused by Meloidogyne incognita on tobacco was calculated as a function of the statistical frequency distribution of sample counts. Sampling frequency distributions were described by a negative binomial model, with parameter k, and the resulting probability generating function was used to calculate discrete damage probabilities. Negative binomial damage predictions were compared to mean-density estimates of damage. Predictions based on mean density alone overestimate yield loss by values ranging from 300% at a k of 0.1 to less than 10% at a k of 1.0. Damage overestimation was described as an exponential function of k and mean density. Preplant sampling data for M. incognita were used to derive a linear model for the estimation of k from mean density, allowing the calculation of yield-loss overestimation based on one parameter, the field mean density. Overestimation of damage ranged from 288% at a density of 50 juveniles/500 cm(3) soil, to 5% at a density of 1,000 juvelfiles/500 cm(3) soil.