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Open access publications by faculty, staff, postdocs, and graduate students from the Cooperative Extension.
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Item First Report of Chagas Disease Vector Species Triatoma sanguisuga (Hemiptera: Reduviidae) Infected with Trypanosoma cruzi in Delaware(The American Journal of Tropical Medicine and Hygiene, 2024-03-26) Peterson, Jennifer K.; Hoyos, Juliana; Bartlett, Charles R.; Gottdenker, Nicole L.; Kunkel, Brian; Murphy, Carrie; Alvarado, AntonioIn July and October 2023, two live triatomine bugs were found inside a home in New Castle County, Delaware. The bugs were identified as Triatoma sanguisuga, the most widespread triatomine bug species in the United States. Triatoma sanguisuga is a competent vector of Trypanosoma cruzi, the causative agent of Chagas disease. The two specimens were tested via real-time PCR (qPCR) for infection with T. cruzi, and one of the specimens was positive. Despite T. sanguisuga being endemic to the area, attainment of accurate species identification and T. cruzi testing of the bugs required multiple calls to federal, state, private, and academic institutions over several months. This constitutes the first report of T. sanguisuga infected with T. cruzi in Delaware. In addition, this is the first published report of T. sanguisuga in New Castle County, the northernmost and most densely populated county in Delaware. New Castle County still conforms to the described geographic range of T. sanguisuga, which spans from Texas to the East Coast of the United States. The T. cruzi infection prevalence of the species has not been studied in the northeastern United States, but collections in southern states have found prevalences as high as 60%. The Delaware homeowner’s lengthy pursuit of accurate information about the vector highlights the need for more research on this important disease vector in Delaware.Item Assessing relationships of cover crop biomass and nitrogen content to multispectral imagery(Agronomy Journal, 2024-02-29) Miller, Jarrod O.; Shober, Amy L.; Taraila, JamieCover crops provide valuable roles in sustainable agriculture, provided they produce enough biomass. To accurately measure their services to field management, spatial estimates would be useful to producers. This study used multispectral drone imagery to produce maps of normalized difference vegetation index (NDVI), normalized difference red edge index (NDRE), and a digital surface model (DSM) of cover crop plots on sandy, Mid-Atlantic soils. Cover crops included cereal rye (Secale cereale), mixtures of rye and crimson clover (Trifolium incarnatum), and mixtures of rye and hairy vetch (Vicia villosa). Their biomass was sampled in the spring of 2019, 2020, and 2021, dried, weighed, and analyzed for total nitrogen (N) content. Measurements of NDVI became saturated (i.e., reached a linear plateau) at 3.86 Mg biomass ha−1, NDRE at 5.72 Mg biomass ha−1, and the DSM at 5.11 Mg biomass ha−1. The measured N content became saturated at 80.9, 139.1, and 75 kg N ha−1 for NDVI, NDRE, and the DSM, respectively. Based on log transformations, NDVI was a stronger predictor of biomass and N, but not C:N. The NDRE was important for biomass, N, and C:N, while the DSM interactions with cover crop species helped predict both the N content and C:N of cover crop tissues. Accumulated growing degree days was important as an individual variable for biomass and N and as an interaction with cover crop species. Abbreviations DSM digital surface model GDD growing degree days NDRE normalized difference red edge index NDVI normalized difference vegetation indexItem Post-harvest drone flights to measure weed growth and yield associations(Agricultural & Environmental Letters, 2022-06-14) Miller, Jarrod O.; Shober, Amy L.; VanGessel, Mark J.Drone flights are often only performed during the growing season, with no data collected once harvest has been completed, although they could be used to measure winter annual weed growth. Using a drone mounted with a multispectral sensor, we flew small plot corn (Zea mays L.) fertility, cover crop, and population studies at black layer and 0–14 d after harvest (DAH). Yields had positive correlations to normalized difference vegetation index (NDVI) at black layer but often had negative correlations to corn yields 0–14 DAH. After harvest, NDVI could be associated with weed growth, and negative correlations to yield could point to reduced corn canopy allowing light to reach late-season weeds. In fertility studies, excess nitrogen appears to increase weed biomass after harvest, which can be easily identified through drone imagery. Flights should be performed after corn harvest as weed growth may provide additional insight into management decisions. Core Ideas: - Corn yields can be correlated to post-harvest weed biomass by using NDVI. - Drone flights efficiently mapped weeds and made correlations to yield and management. - Fall weed control can be prioritized using drone mapping. Abbreviations: DAH days after harvest LAI leaf area index NDVI normalized difference vegetation indexItem Improving targeting of farmers for enrollment in agri-environmental programs(Applied Economic Perspectives and Policy, 2023-05-18) Duke, Joshua M.; Johnston, Robert J.; Shober, Amy L.; Liu, ZhongyuanAgricultural cost-share research and planning tend to focus on one program at a time, and hence overlook additional efficiencies that might be obtained by considering the possibility that enrollment decisions are related across different programs. Models of multiple-program participation decisions enable these relationships to be considered as part of conditional enrollment predictions, providing more complete and accurate understanding of enrollment behavior. Analysis of data from farmer surveys in Maryland and Ohio show complementary drivers across program participation. Results are consistent with economies of scale and/or scope among different agri-environmental programs. The data also show the gains in prediction accuracy when the model accounts for participation in other programs, thereby enabling improved targeting and program design. For instance, enrollment in commodity-type programs causes a much larger marginal increase (12.6%) in the probability of Maryland cover crops participation than does the increase from Conservation Reserve Program enrollment (4.4%).Item Soil health tradeoffs may be minimal in phosphorus-enriched Coastal Plain soils(Agricultural & Environmental Letters, 2023-03-31) Mosesso, Lauren R.; Shober, Amy L.Soil health practices can improve soil conditions and provide ecosystem services, but increased risk of phosphorus (P) loss can be an unintended consequence. We investigated conservation tillage and cover crops effects on soil P stratification, P accumulation at depth, and soil aggregation for sandy Coastal Plain soils from the Mid-Atlantic United States soil cores from 10 agricultural fields with 0–15 years of conservation tillage or cover cropping were analyzed for Mehlich-3 P and dry aggregate stability. We found no evidence that conservation tillage or cover cropping caused P stratification or accumulation in study fields that were already enriched with P prior to soil health implementation. Annual particulate, dissolved runoff, and leachate P loads decreased when estimated using the North Carolina Phosphorus Loss Assessment Tool assuming no-till and cover crops (soil health) compared to conventional till and winter fallow (conventional). We suggest that soil health practices are unlikely to exacerbate P losses from high P Coastal Plain soils beyond their initial risk profile. Core Ideas: - Soil health practices may increase the risk of surface and subsurface phosphorus (P) loss in P-enriched soils. - Soil P stratification in 10 fields with and without soil health practices were compared. - There is no evidence that soil health practices increased the risk for dissolved soil P losses. - Soil health practices may reduce P loads in fields with significant sources of dissolved P. Abbreviations: DP dissolved phosphorus NC-PLAT North Carolina Phosphorus Loss Assessment Tool PP particulate phosphorusItem First report of Rhizoctonia solani AG 4 causing brown bean of lima bean in Delaware(Plant Disease, 2022-06-11) Ginn, Adam Nicholas; Evans, Tom; Ernest, Emmalea; Koehler, Alyssa M.Lima bean production has been an economically valuable staple in Delaware agriculture for almost a century, with annual revenue approaching 8 million dollars (USDA-NASS, 2019; Evans et al. 2007). From 2019-2021, lima beans displaying symptoms of brown discoloration, referred to as “brown bean” were observed in the green baby lima variety ‘Cypress’ across multiple commercial and research fields. Symptoms were present in approximately 1-5% of beans and not visible until pods were opened for harvest. Thirty-seven symptomatic beans were collected and surface disinfested in 0.85% sodium hypochlorite for 30 s, rinsed in sterile deionized water for 30 s, sectioned into four pieces and plated onto potato dextrose agar (PDA) amended with 50 µg/ml penicillin G and streptomycin sulfate. Petri dishes were incubated at 23ºC and observed for colony morphology. Pure cultures were obtained with tan colonies that had mycelia with right angle branching and septations near the branch, consistent with the description of Rhizoctonia solani Kuhn (Sneh et al. 1991). DNA extraction and pathogen identification was confirmed by sequencing of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA using primers ITS4/ITS5 (White et al. 1990) for thirty-seven isolates collected in 2019 and 2020. Isolates were identified as Rhizoctonia solani AG 4 (99.9% sequence identity with GenBank Accession [MN106359.1].) A representative isolate was selected to complete Koch’s postulates and the sequence was deposited in GenBank as accession number MW560551. To observe colonization ability, 10 detached pods were sterilized in 75% EtOH for 60 s, then rinsed in Milli-Q water. The detached pods were divided among two 150 mm Petri dishes containing a single 150 mm filter paper saturated with Milli-Q water. Five 1 mm2 agar plugs colonized with the representative R. solani isolate were placed 0.5 cm apart along the length of the pod. Plates were sealed with parafilm and left at room temperature. Control pods were kept in identical conditions but inoculated using clean agar plugs. The trial was repeated and a second trial was conducted on 12 attached asymptomatic pods from C-Elite Select lima bean plants at the succulent seed stage to complete Koch’s Postulates. Pods were surface disinfested with 70% ethanol. Three attached pods were wounded with the tip of a sterile scalpel blade where a colonized agar plug was placed and loosely wrapped with a thin parafilm layer to maintain contact. Three attached pods not wounded were also inoculated with a colonized agar plug and wrapped by parafilm. Three wounded and non-wounded pods received clean agar plug controls. Both attached and detached pods were kept at room temperature for one week until symptoms began to manifest on the pod surfaces, at which point the beans from infected pods were removed and placed on PDA, three to a plate. In the attached assay, all beans of both wounded and non-wounded pods developed symptoms. The plates were stored in identical conditions and monitored for 5 days until tan colonies were observed. Culture morphology was consistent with the original isolate in all beans. Sequencing of the ITS region confirmed identity as R. solani AG-4. No symptoms were observed on control pods or seeds. Rhizoctonia solani is most frequently associated with symptoms of root rot (Sharma-Poudyal et al. 2015), but no stem symptoms are associated with the late season “brown bean” that has been observed throughout production in recent years. To our knowledge, this is the first report of Rhizoctonia solani AG 4 causing symptoms of brown bean of lima bean in Delaware. In preliminary observations, symptoms seem to be worse in pods that could have had contact with the soil directly or via rain splash. This disease cannot be detected until pods are split open, which has potential to reduce lima bean quality at harvest. Further monitoring should be conducted to quantify yield impacts and develop appropriate preventative and curative techniques.