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Browsing by Author "Langston, David B."

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2021 Field Crops PMG
Balota, Maria; Besancon, Thierry E.; Cahoon, Charles W.; Chandra, Rakesh; Currin, John F.; Day, Eric R.; Flessner, Michael; Frame, William Hunter, 1985-; Frank, Daniel; Hines, Tommy; Herbert, D. Ames Jr.; Johnson, Charles S.; Johnson, Quintin; Jordan, David; Koehler, Alyssa; Langston, David B.; Lamb, Curt; Lingenfelter, Dwight; McCoy, Tim; Singh, Vijay; Taylor, Sally V.; VanGessel, Mark; Vollmer, Kurt; Wallace, John M.; Wilson, James (Virginia Cooperative Extension, 2021-02-12)
The Virginia Pest Management Guide (PMG) series lists options for management of major pests: diseases, insects, nematodes, and weeds. These guides are produced by Virginia Cooperative Extension and each guide is revised annually. PMG recommendations are based on research conducted by the Research and Extension Division of Virginia Tech, in cooperation with other land-grant universities, the USDA, and the pest management industry. Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products that also may be suitable.
2021 Field Crops PMG - Disease and Nematode Management
Langston, David B.; Koehler, Alyssa; Johnson, Charles S. (Virginia Cooperative Extension, 2021-02-12)
This is a chapter of the 2021 Field Crops PMG. The Virginia Pest Management Guide (PMG) series lists options for management of major pests: diseases, insects, nematodes, and weeds. These guides are produced by Virginia Cooperative Extension and each guide is revised annually. PMG recommendations are based on research conducted by the Research and Extension Division of Virginia Tech, in cooperation with other land-grant universities, the USDA, and the pest management industry. Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products that also may be suitable.
2021 Home Grounds and Animals PMG - Index
Balota, Maria; Besancon, Thierry E.; Cahoon, Charles W.; Chandran, Rakesh; Currin, John F.; Day, Eric R.; Flessner, Michael; Frame, William Hunter; Frank, Daniel; Hines, Tommy; Herbert, Ames Jr.; Johnson, Charles S.; Johnson, Quintin; Jordan, David; Koehler, Alyssa; Langston, David B.; Laub, Curt; Lingenfelter, Dwight; McCoy, Tim; Singh, Vijay; Taylor, Sally V.; VanGessel, Mark; Vollmer, Kurt; Wallace, John M.; Wilson, James (Virginia Cooperative Extension, 2021-02-12)
This is a chapter of the 2021 Field Crops PMG. The Virginia Pest Management Guide (PMG) series lists options for management of major pests: diseases, insects, nematodes, and weeds. These guides are produced by Virginia Cooperative Extension and each guide is revised annually. PMG recommendations are based on research conducted by the Research and Extension Division of Virginia Tech, in cooperation with other land-grant universities, the USDA, and the pest management industry. Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products that also may be suitable.
2021 Virginia Peanut Production Guide
Balota, Maria; Jordan, David; Langston, David B.; Shortridge, Julie; Taylor, Sally V. (Virginia Cooperative Extension, 2021-02-09)
This publication included a guide for peanut growers including agronomic, insect, disease management along with weed control, and irrigation and safety information. Archived Peanut Production Guides can be accessed from: http://www.sites.ext.vt.edu/newsletter-archive/peanut-production/index.html
2021 Virtual Eastern Shore Agricultural Conference and Trade Show
Pittman, Theresa; Deitch, Ursula T.; Reiter, Mark S.; Singh, Vijay; Mason, John; Duerksen, Keren; Haymaker, Joseph; Doughty, Helene; Holshouser, David Lee, 1963-; Langston, David B.; Flessner, Michael; Rideout, Steven L.; Thomason, Wade E.; McCullough, Chris T.; Sutton, Kemper L.; Bekelja, Kyle; Kuhar, Thomas P.; Richardson, Bruce; Harper, Robert; Richardson, Brett; Shockley, Bill (Virginia Cooperative Extension, 2021-03-12)
Join us for the 2021 virtual Eastern Shore Agricultural Conference and Trade Show! Hear updates and continuing education presentations that are pertinent to Eastern Shore of Virginia growers.
2022-2023 Mid-Atlantic Commercial Vegetable Production Recommendations
Reiter, Mark S.; Samtani, Jayesh; Torres Quezada, Emmanuel; Singh, Vijay; Doughty, H.; Kuhar, Thomas P.; Sutton, Kemper; Wilson, James; Langston, David B.; Rideout, Steven; Parkhurst, James; Strawn, Laura K. (Virginia Cooperative Extension, 2022-11-30)
This copy of the 2022/2023 Mid-Atlantic Commercial Vegetable Production Recommendations replaces all previous editions of the Commercial Vegetable Production Recommendations published individually for Delaware, Maryland, New Jersey, Pennsylvania, Virginia, and West Virginia. Information presented in this publication is based on research results from the University of Delaware, the University of Maryland, Rutgers - The State University of New Jersey, The Pennsylvania State University, Virginia Polytechnic Institute and State University, West Virginia University, and the U.S. Department of Agriculture, combined with industry and grower knowledge and experience. This publication will be revised biennially. In January 2023, a Critical Update with important updates for this publication will be communicated through local Extension Agents and Vegetable Specialists. The editors welcome constructive criticism and suggestions from growers and industry personnel who may wish to help improve future editions of this publication. These recommendations are intended for the commercial vegetable grower who has to make numerous managerial decisions. Although the proper choices of variety, pesticides, equipment, irrigation, fertilizer, and cultural practices are the individual vegetable grower’s responsibility, it is intended that these recommendations will facilitate decision-making. Recommended planting dates will vary across the six-state region. Local weather conditions, grower experience, and variety may facilitate successful harvest on crops planted outside the planting dates listed in this guide. This can be evaluated in consultation with the local agents and state specialists. Government agencies and other organizations administrating crop insurance programs or other support programs should contact local Extension agents and/or vegetable specialists for guidance. Not to be used by home gardeners.
Alternatives to chlorpyrifos in Virginia type peanut production for control of southern corn rootworm
Hoar, Elijah Kael (Virginia Tech, 2024-06-05)
Historically, the organophosphate insecticide chlorpyrifos was used to protect peanuts (Arachis hypogaea L.) from soil-dwelling insect pests. In 2022, its registration was canceled by the Environmental Protection Agency (EPA) for all food crops. The southern corn rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae) (SCR), was the major pest of developing peanut previously managed by chlorpyrifos and there are no known alternative insecticides for its control. The SCR larvae can cause economic damage by feeding on developing pods and pegs. Field condition is an important factor in SCR survival as the larvae rely on soil moisture to survive, and larvae cannot feed on fully developed pods. The dependency of SCR on soil moisture and host availability allows for cultural modifications (e.g., planting date, judicious irrigation practices, selecting fields based on soil characteristics) to reduce losses to this pest. Alternatively, or in addition to these strategies, identifying varieties with resistance to SCR can provide growers with non-chemical methods to mitigate losses. Therefore, this project was developed to identify sources of resistance in commercial cultivars and advanced breeding lines of Virginia type peanuts to SCR and examine whether early digging can reduce SCR injury. Implementing an effective integrated pest management (IPM) plan relies on a clear understanding of the pest life cycle in relation to the susceptible stage of the crop. We also evaluated SCR phenology in relation to peanut development. Replicated field trials were used to screen cultivars and investigate the effect, if any, of early digging in reducing pod injury. We monitored SCR adult populations over time using sticky traps. Our research will help manage a problematic pest in this region with limited, or no, reliance on insecticides.
Applied Research on Field Crop Disease & Nematode Management 2020
Langston, David B. (Virginia Cooperative Extension, 1899-12-30)
This publication provides a summary of applied research conducted in 2020 on disease and nematode management in wheat, corn, cotton, peanut, and soybean.
Characterization, development of a field inoculation method, and fungicide sensitivity screening of the Pythium blight pathogen of snap bean (Phaseolus vulgaris L.)
Harrison, Leigh Ann (Virginia Tech, 2011-03-08)
New Jersey, Georgia, and the Eastern Shore of Virginia (ESV) are important snap bean (Phaseolus vulgaris L.) growing regions, but profitability is threatened by Pythium blight. Causal agents of Pythium blight on snap bean were identified using morphological characterization and sequence analysis of the rDNA-internal transcribed spacer (ITS) regions of 100 isolates. Most isolates were Pythium aphanidermatum (Edson) Fitzp. (53%), and also included Pythium deliense Meurs (31%; all from Georgia), Pythium ultimum Trow (12%), Pythium myriotylum Drechsler (2%), Pythium catenulatum Matthews (1%), and unknown Pythium sp. (1%). To our knowledge, this is the first report of P. deliense in Georgia and on common bean and squash (Cucurbita pepo L.); as well as the first report of P. catenulatum on lima bean (Phaseolus lunatus L.) and in New Jersey. Fungicide labeling and cultivar selection for Pythium blight management is hindered by difficulties associated with conducting successful trials, because the disease occurs sporadically and clustered in the field. Three P. aphanidermatum-infested inoculum substrates were evaluated at three concentrations. The vermiculite/V8 juice (5:3 weight to volume) inoculum (10,000 ppg/0.3 m) consistently caused at least 50% disease in 3 field trials. Sensitivity of the Pythium blight pathogens was determined in vitro against five fungicides. Twenty-two Pythium isolates representing P. aphanidermatum, P. deliense, P. ultimum, and P. myriotylum were inoculated to media amended with each active ingredient at 0, 100μg/ml, the concentration equivalent to the field labeled rate if applied on succulent beans at 187 L/ha, and the equivalent if applied at 374 L/ha. All isolates were completely sensitive (100% growth reduction, or GR) to all active ingredients at the labeled rates, except azoxystrobin. At 100μg/ml azoxystrobin, one P. deliense isolate had 8.9% GR. All isolates had 100% GR to copper hydroxide at 100μg/ml, and the lowest GR on mefenoxam-amended medium was 91.9%. At 100μg/ml cyazofamid, all P. deliense isolates were completely sensitive and variation was observed in P. aphanidermatum isolates. At 100μg/ml potassium phosphite, significant GR similarities were recorded within isolates of the same species, and less than 50% GR was observed in all P. deliense isolates.
Comparison of 2,4-D, dicamba and halauxifen-methyl alone or in combination with glyphosate for preplant weed control
Askew, M. Carter; Cahoon, Charles W. Jr.; York, Alan C.; Flessner, Michael L.; Langston, David B.; Ferebee, J. Harrison (2021-02)
A field study was conducted in 2017 and 2018 to determine foliar efficacy of halauxifen-methyl, 2,4-D, or dicamba applied alone and in combination with glyphosate at preplant burndown timing. Experiments were conducted near Painter, VA; Rocky Mount, NC; Jackson, NC; and Gates, NC. Control of horseweed, henbit, purple deadnettle, cutleaf evening primrose, curly dock, purple cudweed, and common chickweed were evaluated. Halauxifen-methyl applied at 5 g ae ha(-1) controlled small and large horseweed 89% and 79%, respectively, and was similar to control by dicamba applied at 280 g ae ha(-1). Both rates of 2,4-D-533 g ae ha(-1)(low rate [LR]) or 1,066 g ae ha(-1) (high rate [HR])-were less effective than halauxifen-methyl and dicamba for controlling horseweed. Halauxifen-methyl was the only auxin herbicide to control henbit (90%) and purple deadnettle (99%). Cutleaf evening primrose was controlled 74% to 85%, 51%, and 4% by 2,4-D, dicamba, and halauxifen-methyl, respectively. Dicamba and 2,4-D controlled curly dock 59% to 70% and were more effective than halauxifen-methyl (5%). Auxin herbicides applied alone controlled purple cudweed and common chickweed 21% or less. With the exception of cutleaf evening primrose (35%) and curly dock (37%), glyphosate alone provided 95% or greater control of all weeds evaluated. These experiments demonstrate halauxifen-methyl effectively (>= 79%) controls horseweed, henbit, and purple deadnettle, whereas common chickweed, curly dock, cutleaf evening primrose, and purple cudweed control by the herbicide is inadequate (<= 7%).
Comparison of Current Peanut Fungicides Against Athelia rolfsii Through a Laboratory Bioassay of Detached Plant Tissues
Wei, Xing; Langston, David B.; Mehl, Hillary L. (American Phytopathological Society, 2022-08)
Southern stem rot of peanut, caused by Athelia rolfsii, is an important fungal disease that impacts peanut production worldwide. Foliar-applied fungicides are used to manage the disease, and several fungicides have been recently registered for southern stem rot control in peanuts. This study compared fungicidal, residual, and potential systemic activity of current fungicides against A. rolfsii using a laboratory bioassay. Peanut plants grown in the field were treated with eight fungicides approximately 90 days after planting, and plants were collected for the laboratory bioassay weekly for 5 weeks following application. Peanut plants were separated into the newest fully mature leaf present at sample collection, the second newest fully mature leaf present at the time of fungicide application, the upper stem, and the crown tissues. Each plant tissue was inoculated with A. rolfsii then incubated at 30 degrees C for 2 days. Lesion length was measured, and percent inhibition of fungal growth by each fungicide relative to the control was calculated. All fungicides provided the greatest inhibition of A. rolfsii on leaf tissues that were present at the time of fungicide application, followed by the newly grown leaf and upper stem. Little inhibition occurred on the crown. Fungal inhibition decreased at similar rates over time for all fungicides tested. Succinate dehydrogenase inhibitors provided less basipetal protection of upper stems than quinone outside inhibitor or demethylation inhibitor fungicides. Properties of the fungicides characterized in this study, including several newly registered products, are useful for developing fungicide application recommendations to maximize their efficacy in controlling both foliar and soilborne peanut diseases.
Efficacy of Organic Fungicides for Control of Powdery Mildew, Downy Mildew, and Plectosporium in Pumpkins
Simmons, Trevor; Baudoin, Antonius B.; Langston, David B.; Welbaum, Gregory E. (Virginia Tech, 2017-05-02)
Increased agritourism in the state of Virginia has led to an increase in the pumpkin planting acreage for pick-your-own operations across the commonwealth. Virginia pumpkin producers face yield losses from numerous sources, including several fungal diseases. The objective of this research was to compare the efficacy of certified organic fungicides against a conventional fungicide program for the control of powdery mildew, downy mildew, and plectosporium. Cultivar Warty Goblin pumpkins were grown in Rockville, Virginia during the 2016 crop season. Five different treatments (water, Kaligreen, Nordox, Regalia, and Bravo +Quintec/Proline) were assessed for their control of powdery mildew, downy mildew, and plectosporium. Disease observations and treatments were made weekly from August 12 – September 15. Disease ratings for powdery mildew showed that conventional fungicides provided the greatest control, with organic products Kaligreen and Nordox providing next-best control, statistically equivalent in some analyses. Regalia did not provide significantly better disease control than untreated water controls. Plectosporium disease severity was reduced the most in plots receiving conventional fungicides, with Nordox being almost as effective. Kaligreen provided no control of plectosporium. Regalia provided modest control, which in some analyses was significantly better than the untreated control. Downy mildew pressure was extremely limited, and no significant differences in disease incidence were seen among the treatments. In conclusion, several of the tested organic materials proved to be statistically as effective as the conventional fungicides in controlling both powdery mildew and plectosporium, although conventional fungicides provided numerically superior control for all diseases.
An Evaluation of Eight Basil Cultivars for Downy Mildew Resistance in Virginia
Cooper, Jason (Virginia Tech, 2019-12-23)
Production of fresh herbs is a trendy market that continues to grow in popularity in the United States. Basil (Ocimum baasilicum) is such an herb that is experiencing growth in popularity, especially sweet basil. In Virginia, sweet basil production is increasing and can occur both within the field and greenhouses. However, basil production faces certain challenges, with the most serious one being disease losses caused by downy mildew. With few effective control measures available it is important to find management practices that can assist in controlling this disease, particularly in organic systems. Thus, studies were performed examining eight different sweet basil cultivars during the summer growing season of 2019. The study took place at Adam’s Apples and Herbs, located in Shenandoah County in the Shenandoah Valley of Virginia and at Virginia Tech’s Eastern Shore Agricultural Research and Extension (ESAREC) in Painter. At harvest, basil was weighed, by leaf and by stem, and then an average of the weight was calculated as was the height of each cultivar. Disease incidence and severity for each basil cultivar was recorded throughout the course of the study. Little disease occurred during the course of the study in the Shenandoah Valley. However, significant differences in basil cultivar growth and appearance were noted. At the ESAREC, downy mildew did develop and resistant cultivars proved to be effective at suppressing disease.
An Evaluation of Eight Pumpkin Varieties in Central Virginia
Sharpe, Sarah E.W.; Scoggins, Holly L.; Langston, David B.; Rideout, Steven L. (Virginia Tech, 2019-05-24)
Pumpkin production is on the rise in Virginia. Pumpkins make up 8.4% of the total market value of all vegetables sold in the state and acres in production of pumpkins increased by 5.2% from 2007 to 2012. Types of pumpkin production methods, insect, disease, and weed management, pollination, and harvest and post-harvest management all must be considered by pumpkin producers. Unfortunately, pumpkin cultivar performance in the Mid-Atlantic is not well documented. Thus, a variety study was performed using eight different pumpkin varieties over the 2017 and 2018 growing seasons. The study took place at JETT Farms, Inc., located in Madison County in the Central Virginia area. At harvest, pumpkins were counted and weighed, and then an average and total fruit weight was calculated for each cultivar.
Evaluation of organic fungicides for management of pumpkin diseases, 2016.
Simmons, T. P.; Baudoin, Antonius B.; Langston, David B.; Welbaum, Gregory E.; West, J. L. (2016)
The trial took place at a commercial farm in Rockville, VA. The soil was a Cecil fine sandy loam. Herbicide and fertilizer were applied according to Virginia Cooperative Extension recommendations. Additional hand-weeding was performed weekly as needed. Five rows of cultivar Warty Goblin were planted on 1 Jul, with intra-row spacing of 4 ft and inter-row spacing of 9 ft. To ensure 100% stand, plots were planted at a higher-than-normal population density. Every 4 ft within each row there were two pumpkin plants, instead of one; although different from commercial recommendations, this method of over-seeding to ensure 100% stand is common practice for the farm on which research was performed. A randomized complete block design was used with four replicates of each treatment. Chemical applications were made using a backpack sprayer with a handheld 4-nozzle spray boom configuration with Teejet 8002VS tips spaced at 18 in. All chemicals were applied using a carrier rate of 20 gal of water per acre at 35 psi. Treatments were applied 5 Aug, 12 Aug, 19 Aug, 16 Aug, 2 Sep, and 9 Sep. Presidio at 4 oz/A was applied to all treatments (including the control) on 19 Aug to control downy mildew. Nordox 75WG was mistakenly applied at a higher than labeled rate (1.5 lb/A rather than 1.25 lb/A) due to a misunderstanding about the formulation involved. Disease severity on leaves, stems and fruit of the four centrally located pumpkin plants in each plot was rated weekly starting on 12 Aug. Individual disease ratings showed distinct relationships between means and standard deviations, and no single transformation performed best with respect to homogenizing variances. Areas under the disease progress curve (AUDPC) were calculated for the last 3 weeks by summing disease ratings for each plot, and equality of variance was tested. JMP 13’s Fit Y by X platform was used to fit a generalized linear model using a Poisson distribution. Since the data were somewhat over-dispersed, the overdispersion factor was used to adjust the test statistics, and the Holm-Bonferroni correction was applied to adjust the overall error rate. Precipitation was slightly above normal for July (5.46 in. average of four Weather Underground stations located 4-17 miles from the trial site in different directions) but below normal for August (2.72 in.) and the first half of September (0.41 in.).
Field Crops: 2022 Pest Management Guide
Besancon, Thierry E.; Cahoon, Charlie; Chandran, Rakesh; Currin, John F.; Day, Eric R.; Flessner, Michael; Frame, William Hunter; Frank, Daniel; Hines, Tommy; Johnson, Quintin; Jordan, David; Koehler, Alyssa; Langston, David B.; Lingenfelter, Dwight; Reed, T. David; Singh, Vijay; Taylor, Sally V.; VanGessel, Mark; Vollmer, Kurt; Wallace, John M.; Wilson, James M. (2022-02-03)
Identifying Optimal Wavelengths as Disease Signatures Using Hyperspectral Sensor and Machine Learning
Wei, Xing; Johnson, Marcela A.; Langston, David B.; Mehl, Hillary L.; Li, Song (MDPI, 2021-07-19)
Hyperspectral sensors combined with machine learning are increasingly utilized in agricultural crop systems for diverse applications, including plant disease detection. This study was designed to identify the most important wavelengths to discriminate between healthy and diseased peanut (Arachis hypogaea L.) plants infected with Athelia rolfsii, the causal agent of peanut stem rot, using in-situ spectroscopy and machine learning. In greenhouse experiments, daily measurements were conducted to inspect disease symptoms visually and to collect spectral reflectance of peanut leaves on lateral stems of plants mock-inoculated and inoculated with A. rolfsii. Spectrum files were categorized into five classes based on foliar wilting symptoms. Five feature selection methods were compared to select the top 10 ranked wavelengths with and without a custom minimum distance of 20 nm. Recursive feature elimination methods outperformed the chi-square and SelectFromModel methods. Adding the minimum distance of 20 nm into the top selected wavelengths improved classification performance. Wavelengths of 501–505, 690–694, 763 and 884 nm were repeatedly selected by two or more feature selection methods. These selected wavelengths can be applied in designing optical sensors for automated stem rot detection in peanut fields. The machine-learning-based methodology can be adapted to identify spectral signatures of disease in other plant-pathogen systems.
Impact Assessment of Nematode Infestation on Soybean Crop Production Using Aerial Multispectral Imagery and Machine Learning
Jjagwe, Pius; Chandel, Abhilash K.; Langston, David B. (MDPI, 2024-06-24)
Accurate and prompt estimation of geospatial soybean yield (SY) is critical for the producers to determine key factors influencing crop growth for improved precision management decisions. This study aims to quantify the impacts of soybean cyst nematode (SCN) infestation on soybean production and the yield of susceptible and resistant seed varieties. Susceptible varieties showed lower yield and crop vigor recovery, and high SCN population (20 to 1080) compared to resistant varieties (SCN populations: 0 to 340). High-resolution (1.3 cm/pixel) aerial multispectral imagery showed the blue band reflectance (r = 0.58) and Green Normalized Difference Vegetation Index (GNDVI, r = −0.6) have the best correlation with the SCN populations. While GDNVI, Green Chlorophyll Index (GCI), and Normalized Difference Red Edge Index (NDRE) were the best differentiators of plant vigor and had the highest correlation with SY (r = 0.59–0.75). Reflectance (REF) and VIs were then used for SY estimation using two statistical and four machine learning (ML) models at 10 different train–test data split ratios (50:50–95:5). The ML models and train–test data split ratio had significant impacts on SY estimation accuracy. Random forest (RF) was the best and consistently performing model (r: 0.84–0.97, rRMSE: 8.72–20%), while a higher train–test split ratio lowered the performances of the ML models. The 95:5 train–test ratio showed the best performance across all the models, which may be a suitable ratio for modeling over smaller or medium-sized datasets. Such insights derived using high spatial resolution data can be utilized to implement precision crop protective operations for enhanced soybean yield and productivity.
Investigating Management Alternatives for Southern Blight on Vegetables in the mid-Atlantic United States
Garcia Gonzalez, Jose Francisco (Virginia Tech, 2021-05-25)
Incidence and severity of southern blight caused by Sclerotium rolfsii Sacc. is increasing in the mid-Atlantic region of the U.S. affecting both conventional and organic vegetable production systems. Traditional southern blight management relied on fumigants and fungicides with often inconsistent and uneconomical results. Moreover, with the phase-out of methyl bromide, and the high cost and toxicity of other available fumigants, it is necessary to identify effective and economical southern blight management alternatives. Therefore, the objectives of this research were to 1) evaluate the effect of planting date and potato (Solanum tuberosum L.) cultivar selection on southern blight incidence and tuber yield and quality; 2) compare potato cultivar tuber susceptibility to S. rolfsii in post-harvest settings; and 3) assess the suitability of six cool-season cover crop biomasses and three locally organic materials as carbon sources for anaerobic soil disinfestation (ASD) treatments and their impact on S. rolfsii viability and soil. In a three-year field study, ten commercial potato cultivars and four planting dates per year were evaluated on the Eastern Shore of Virginia. Later potato plantings generally produced greater disease incidence (85-94%) and lower tuber yield (1.8-9.4 Mg ha-1) and quality (47-78%), likely driven by humid, warm weather later in the season that was conducive to disease and detrimental to the potato crop. While no potato cultivar was completely immune to S. rolfsii incidence, cultivar 'Accumulator' consistently had one of the lowest disease incidences (12-71%) and greatest tuber yield among cultivars (6.2-37.3 Mg ha-1), and 'Adirondack Blue' and 'Red Norland' had the overall greatest disease incidence (33-100%). Following harvest of the field experiment, the susceptibility of tubers from the ten cultivars to post-harvest rot caused by S. rolfsii was compared in a laboratory experiment under controlled conditions. 'Atlantic' followed by 'Accumulator' were the least susceptible (3.7-12.6 g of diseased tissue) whereas 'Adirondack Blue', followed by red-skinned potato cultivars had the greatest severity of post-harvest tuber rot (12-17.5 g of diseased tissue). Following three weeks of ASD treatments in growth chamber pot experiments utilizing nine carbon sources incubated at 15/25°C 12/12-h cycle, most carbon sources induced soil anaerobicity (33-90 % iron oxide paint removal), but they did not reduce sclerotial viability compared to nonamended aerobic controls. However, most amended soils undergoing ASD induced greater soil microbial activity (0.7-2.0 % CO2 in vol.) compared to nonamended controls (0.1-0.7 CO2 in vol.), increased soil pH, and some amendments increased soil nitrate accumulation. Overall, results of these studies indicate that southern blight can be effectively managed in potato by coupling early planting dates with cultivar selection, but though promising, additional studies are needed to determine the parameters to effectively decrease S. rolfsii viability with ASD treatments.
Management of stem rot of peanut using optical sensors, machine learning, and fungicides
Wei, Xing (Virginia Tech, 2021-05-28)
Stem rot of peanut (Arachis hypogaea L.), caused by a soilborne fungus Athelia rolfsii (Curzi) C. C. Tu and Kimbr. (anamorph: Sclerotium rolfsii Sacc.), is one of the most important diseases in peanut production worldwide. Though new varieties with increased partial resistance to this disease have been developed, there is still a need to utilize fungicides for disease control during the growing season. Fungicides with activity against A. rolfsii are available, and several new products have been recently registered for control of stem rot in peanut. However, fungicides are most effective when applied before or during the early stages of infection. Current scouting methods can detect disease once signs or symptoms are present, but to optimize the timing of fungicide applications and protect crop yield, a method for early detection of soilborne diseases is needed. Previous studies have utilized optical sensors combined with machine learning analysis for the early detection of plant diseases, but these studies mainly focused on foliar diseases. Few studies have applied these technologies for the early detection of soilborne diseases in field crops, including peanut. Thus, the overall goal of this research was to integrate sensor technologies, modern data analytic tools, and properties of standard and newly registered fungicides to develop improved management strategies for stem rot control in peanuts. The specific objectives of this work were to 1) characterize the spectral and thermal responses of peanut to infection with A. rolfsii under controlled conditions, 2) identify optimal wavelengths to detect stem rot of peanut using hyperspectral sensor and machine learning, and 3) evaluate the standard and newly registered peanut fungicides with different modes of action for stem rot control in peanuts using a laboratory bioassay. For Objective 1, spectral reflectance and leaf temperature of peanut plants were measured by spectral and thermal sensors in controlled greenhouse experiments. Differences in sensor-based responses between A. rolfsii-infected and non-infected plants were detected 0 to 1 day after observation of foliar disease symptoms. In addition, spectral responses of peanut to the infection of A. rolfsii were more pronounced and consistent than thermal changes as the disease progressed. Objective 2 aimed to identify specific signatures of stem rot from reflectance data collected in Objective 1 utilizing a machine learning approach. Wavelengths around 505, 690, and 884 nm were repeatedly selected by different methods. The top 10 wavelengths identified by the recursive feature selection methods performed as well as all bands for the classification of healthy peanut plants and plants at different stages of disease development. Whereas the first two objectives focused on disease detection, Objective 3 focused on disease control and compared the properties of different fungicides that are labeled for stem rot control in peanut using a laboratory bioassay of detached peanut tissues. All of the foliar-applied fungicides evaluated provided inhibition of A. rolfsii for up to two weeks on plant tissues that received a direct application. Succinate dehydrogenase inhibitors provided less basipetal protection of stem tissues than quinone outside inhibitor or demethylation inhibitor fungicides. Overall, results of this research provide a foundation for developing sensor/drone-based methods that use disease-specific spectral indices for scouting in the field and for making fungicide application recommendations to manage stem rot of peanut and other soilborne diseases.

Browsing by Author "Langston, David B."

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