Recipient Organization
CLEMSON UNIVERSITY
(N/A)
CLEMSON,SC 29634
Performing Department
Coastal Res & Education Center
Non Technical Summary
This proposal will focus mainly on three representative vegetable crops grown in South Carolina: slicing cucumber (Cucumis sativus, Cucurbitaceae family), kale (Brassica oleracea var. acephala, Brassicaceae), and eggplant (Solanum melongena, Solanaceae). These three botanical families represent the majority of vegetable crops worldwide. Key diseases on these crops, e.g. downy mildew on cucumber and other cucurbits caused by the oomycete Pseudoperonospora cubensis, Alternaria leaf spot on kale and other vegetable brassicas caused by the fungi Alternaria brassicicola and A. brassicae, and Phomopsis blight on eggplant caused by the fungus Phomopsis vexans, will be targeted, because they are persistent disease problems reported by growers or lack suitable control measures. Improvements in disease management and production economics are obtainable with additional research over a five-year period.The foliar disease downy mildew is recognized as the most important disease on pickling and slicing cucumber in the United States. Cucumber losses are estimated to be 50 to 100% of the possible yield without effective control (Holmes et al. 2015). In South Carolina the value of these losses is $2,300 to $4,600 per acre for slicing cucumbers. Without adequate control measures, net returns are negative for fall crops, when overall yields are low and downy mildew pressure is severe (Keinath 2019). P. cubensis has a high risk of developing resistance to fungicides. The economic impact of fungicide resistance to cucurbit downy mildew affects producers, wholesalers, and consumers. Producers face losses with unsuccessful fungicide applications and yield reductions due to uncontrolled downy mildew while shortened supplies may lead to higher consumer prices.Kale, a nutritious leafy green, has been popular for over a decade. Kale is high in vitamins A, C, and K, and calcium, magnesium, iron, manganese, copper, and selenium (Thavarajah et al. 2019). Alternaria leaf spot, also known as black spot, is a fungal disease of kale and other leafy brassica greens that decreases sales and consumption (Wells 2018). For example, in Kenya, Alternaria brassicicola and A. japonica affected 48.6% of the kale growers surveyed, with mean disease incidence of 17.9% (range 9.3% to 30.3%) among those affected (Rop et al., 2009). In South Carolina, the largest producer of organic kale reported this disease as the most important disease problem, particularly in the fall (anon. pers. comm., Jan. 24, 2020; Smith and Keinath, 2004). This directly translates to economic losses to marketing outlets (distributors) and growers. The impacts of this disease on kale producers and the resulting economic losses have not been studied in the United States.Currently, many growers can identify the previously mentioned diseases in their fields, but they fail to understand the true potential for disease to spread, leading to an underestimation of effects on total production and profit. Therefore, an accurate economic analysis of production should take into consideration: the likelihood of being affected by the disease, the rate of disease spread, and the potential losses due to the disease. One of the objectives of this project is to develop scouting tools to better track and identify the precise spread of diseases in the field, which will help define the dynamic relationship between disease and farm profitability.Research fields can be divided into quadrats, which can be used to identify the spatial location of monitoring points (Ristaino et al., 1993). However, this monitoring method is not well suited for grower use, so there is an opportunity to develop scouting tools to help growers and researchers. Though many field scouting applications are available that could assist in tracking the incidence and spread of the disease, most rely on mobile GPS and have spatial accuracy limited to around 10 feet (Pongnumkul et al., 2015; Seyyedhasani et al., 2016). This makes it difficult to localize the disease incidence in small fields and where plants are spaced on 3-foot row centers with 9 inches between plants, e.g. kale. Although unmanned aerial vehicle (UAV) mapping is an attractive option to monitor the disease spread, there is a lag between when early symptoms would be visible from the ground and the air (Martinelli et al., 2015).Results obtained from this project will allow us to develop economic models that account for production uncertainty associated with disease and provide information to growers. The scouting tools developed will be used to map the temporal and spatial spread of foliar diseases and could potentially be used by growers to make better management decisions. Long term, the proposed handheld units could allow growers to pinpoint disease "hot spots" in fields and allow them to target these areas for more frequent scouting or extra pesticide applications or to avoid them at harvest.Farmer profitability depends on the management practices used (e.g. plant and row spacing), input use (e.g. biopesticides) discussed above, disease incidence, marketing decisions (e.g. local or distributers), and prices (Vassalos et al., 2013). In addition to estimating farmer profitability under combinations of management practices, we are proposing deeper analyses of production and marketing for cucumber, kale, and eggplant. In this project, we also propose to examine farmers marketing decisions to identify the most profitable strategy under different situations, based on farm location, prices and edaphoclimatic variables.Growers' profits depend on the net price obtained under different marketing strategies associated with different points of sale. The distance from a farm to the point of sale (distributor or direct marketing outlet), which is critical to the decision to sell or not, also will be explored in this project (Figure 1). A few studies have focused on the analyses of marketing decisions (Blandon et al., 2009; Low et al., 2015; DeLong et al., 2019). Low et al. (2015) compared farmers' marketing strategies, including selling their production direct-to-consumers (DTC). The number of farmers using this strategy increased 23.5% between 2002 and 2012, when it represented 7.8% of US farms. This study and data from the 2017 Census of Agriculture indicate that more and more farms are using this marketing strategy. In this proposal, we will compare all possible marketing strategies, prices, and margins obtained, and estimate profits for growers of these three vegetables.This proposal will facilitate a new cross-disciplinary collaboration across plant pathology, agricultural economics, and agricultural engineering to address persistent disease problems in the southern region with a new approach and focus. We will examine disease management from plant pathology, economic, and engineering perspectives, seeking to provide growers with new pest management practices that will potentially improve yields and increase profitability.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
Major Goals and Objectives1.a. Identify the species of Alternaria causing leaf spot on leafy brassica greens and leaf blight on cucurbits in South Carolina.1.b. Design effective and economical disease management practices to improve yields in conventional cucurbit and eggplant production and organic and conventional brassica production.2. Develop methodology for spatial evaluation of within-field spread of foliar pathogens on vegetables.3. Determine the economic impact of diseases such as downy mildew on cucumbers, kale, eggplant and other vegetables. Estimate farmer's profitability under a variety of management practices when diseases are present and marketing strategies.
Project Methods
Objective 1aAlternaria spp. will be isolated from leafy brassicas in spring and fall seasons at the Coastal REC and fields in Lexington County, SC, the county with the largest acreage of leafy brassicas. Isolates from watermelon and cantaloupe will be collected as part of on-going surveys. Isolates will be identified with multilocus genotyping based on ITS, GAPDH, RPB2, and TEF1 (Woudenberg et al. 2013). Objective 1bAlternaria leaf spot on organic kale. Biofungicides and cultivars will be tested in separate experiments. Biofungicides will be applied weekly. Copper and water will be controls. Cultivars recommended for the southeastern United States will be compared to Darkibor, commonly grown in South Carolina (Kemble et al. 2020). Experiments will be randomized complete blocks with three replications. Percentage symptomatic leaf area per plot will be rated visually five times. Lower leaves 3-12 inches long will be removed from five plants in the middle of the row, sorted into three classes (unblemished, 1 spot, and >1 spot), counted, and weighed. An economic analysis of yields will be done (Objective 3). Downy mildew on kale. Fungicides and biofungicides will be tested in spring experiments with procedures described for Alternaria leaf spot. Kale transplanted in Nov. will be a natural source of inoculum for experimental plants transplanted in Feb. Fungicides will be applied every other week with or without potassium phosphite on alternate weeks. Potassium phosphite applied weekly and water will be controls. Leaves will be harvested and sorted in April. If conventional fungicides rotated with phosphite are more effective than phosphite alone, then 3-week intervals for conventional fungicides will be tested in subsequent years.Phomopsis blight on eggplant. Experiments will be done in fall when P. vexans occurs naturally (Keinath, 2020). Whole plots will be fungicides registered on eggplant, primarily FRAC Groups 3, 7, and 11, applied weekly or biweekly depending on the maximum amount allowed (Kemble et al. 2020). Susceptible cultivars Black Beauty (globe) and Millionaire (Japanese) will be transplanted into split plots. Leaf blight severity and defoliation will be rated. Fruit will be graded as healthy or diseased, counted, and weighed. An economic analysis will be done (Objective 3).Downy mildew on slicing cucumber. Spring and fall experiments will ensure that both P. cubensis clades will be represented (Keinath, 2019; Keinath et al., 2019). Isolates in each experiment will be identified with clade-specific primers (D'Arcangelo and Quesada-Ocampo, 2019). Susceptible cultivar Speedway will be sprayed with fungicides to which resistance has been detected (Keinath et al., 2019). Oxathiapiprolin and water will be the controls. Fruit will be harvested 3 times per week for ≥3 weeks, graded, and weighed (USDA, 2018). An economic analysis will be done (Objective 3).Objective 2 Develop methodology for spatial evaluation of within-field spread of foliar pathogens on vegetables.Data collection system and methodology development. We will develop a data collection method with high spatial accuracy for monitoring downy mildew and Alternaria spread at the individual plant level that will allow us to better understand the dynamics of disease spread. This task will require integrating existing technologies into a handheld field scouting tool and utilizing it to record data regarding disease incidence (location, severity, etc.). The required components are an external GPS receiver, data collection interface (cellphone/tablet), and method to process and store the data. Initially, GPS data will be collected and integrated with Collector for ArcGIS (ESRI, Redlands, CA), which is a commercially available data collection application that integrates directly with GIS software for further processing and storage.To obtain GPS data with the required accuracy, two methods will be explored: 1) Collector integrated with an external GPS receiver capable of receiving real-time kinematic corrections; and 2) Post-processed kinematic correction where the GPS corrections from various sources will be applied during post processing. Initial testing and development of the scouting tool will utilize a simulated field with variable plant spacing to assess the accuracy and repeatability of the GPS's. A GIS workflow will then be created to aggregate data (e.g. location, severity, disease, type, photos) from multiple observations. Development will place emphasis on the cost of the scouting tool, accuracy, and the ability to reliably localize multiple points collected from the same plant. Field testing. After initial testing, the developed tools and workflow will be applied to monitor fields of slicing cucumber, kale, or other vegetable crops at Coastal REC. Once disease is detected, fields will be scouted twice a week to record spatial and temporal spread of disease. Spread of the target diseases and its effect on the overall field will be mapped, and spatial statistics will be used to characterize the disease's spatial pattern, similar to Ristaino and Gumpertz (2000). Data will be compared to random sampling, and the impact of sampling frequency and accuracy also will be investigated. Additionally, attempts will be made to map simultaneously two diseases on the same crop, e.g. Alternaria leaf spot and downy mildew on kale or downy mildew and gummy stem blight on cucumber.Objective 3To evaluate the effect of fungicides and other management techniques (treatments) on vegetable yields, we will use two approaches: test of means and regression analysis. This analysis relies on results of Objective 1b. We will test all differences between 2 means- e.g. mean yield of control versus mean yield of treatment with fungicide application, leading to N/2 different tests per vegetable where N is the number of fungicides tested. We will also estimate a regression on yields per vegetable in terms of each treatment (for example, assuming that there are 6 treatments, represents a dummy variable capturing each treatment where t=0,1,2,3,4,5, using Ordinary Least Squares. The regression will allow us to identify the effect of each treatment on yields, in comparison to the control group (no fungicide). A positive marginal effect indicates that, on average, the treatments are associated with greater yields compared to the control group. We will also investigate if there is any interaction between season (edaphoclimatic characteristic) and fungicide. In addition to a pooled regression (all treatments) we will estimate independent regressions, comparing each treatment to the control.An economic analysis will use the outputs from the field experiments, test of means, regression, and separate regressions to identify fungicide effectiveness at maintaining yields and the diffusion of the disease within the farm based on the analysis of Objective 2. It will also incorporate farmers' behavior with respect to fungicide applications, marketing strategies, and the likelihood of the farm being affected by the disease, based on data from grower surveys and the literature.First, we will simulate profit for all treatments given vegetable prices and input prices under two base scenarios - affected (by the disease) and not affected. Second, we will use data obtained via surveys and the field experiments to build farmer yield distributions given each fungicide and marketing strategies. Third, under the affected scenario, we will build sub-scenarios based on disease diffusion in the field experiments from Objective 1 and 2. Profits will vary among treatments and marketing strategies due to yield distribution and disease diffusion within and across farms. Comparison of these scenarios will indicate the optimal fungicide use.