Performing Department
(N/A)
Non Technical Summary
Phomopsis stem canker is a disease that decreases sunflower (Helianthus annuus) yields in Minnesota (MN), Nebraska (NE), North Dakota (ND), and South Dakota (SD), which together account for over 80% of sunflower production in the U.S. Currently, we recommend applying a single dose of Quinone outside Inhibitor (QoI) fungicide during the miniature floral head growth stage of sunflowers to manage this disease. This treatment can significantly reduce the severity of Phomopsis stem canker (up to 30% reduction) and increase yield (by 5%). However, in 2022, we discovered that Diaporthe helianthi, one of the main fungi responsible for Phomopsis stem canker, has developed complete resistance to QoIs due to a G143A mutation (a substitution of glycine (G) with alanine (A) at amino acid position 143). Our long-term research objective is to enhance in-season management of Phomopsis stem canker by adopting an integrated approach and improving farmers' return on investment (ROI). Our project aims to: (1) Determine the prevalence of QoI-resistant strains of D. helianthi and D. gulyae, the fungi causing Phomopsis stem canker, in MN, ND, NE, and SD; (2) Evaluate the effectiveness of foliar fungicides containing Succinate Dehydrogenase Inhibitor (SDHI) as an alternative to QoIs on hybrids resistant to Diaporthe; and (3) Enhance farmers' and agricultural professionals' confidence in managing Phomopsis stem canker by developing and providing Extension tools. The expected outcomes of this project are increased yields and ROI for farmers through the integration of foliar fungicides and Diaporthe-resistant hybrids, while also raising awareness of the possible presence of QoI-resistant strains capable of causing Phomopsis stem canker in their fields.?
Animal Health Component
0%
Research Effort Categories
Basic
40%
Applied
60%
Developmental
0%
Goals / Objectives
Phomopsis stem canker is a significant disease of sunflower (Helianthus annuus L.) in Minnesota (MN), North Dakota (ND), and South Dakota (SD), which are the major sunflower-producing states in the United States, accounting for over 80% of production (Mathew et al. 2022, 2015). Currently, the recommended management strategy for Phomopsis stem canker is to apply a foliar fungicide that contains pyraclostrobin, a Quinone outside Inhibitor (QoI) class of fungicides, during the miniature floral head growth stage of sunflower (Kashyap et al. 2023). However, Mohan et al. (2023a) reported the first case of QoI resistance in Diaporthe helianthi, one of the fungi responsible for causing Phomopsis stem canker in sunflower in the United States. Therefore, it is crucial to monitor the occurrence of Phomopsis stem canker and potential fungicide resistance in the causal pathogens. This will help inform sunflower farmers about the most effective disease management strategies and reduce yield loss in the future. Additionally, it is important to conduct further research into integrated pest management (IPM) approaches, such as planting Diaporthe-resistant hybrids and alternating the use of fungicides with different chemistry groups. These approaches are crucial for sustaining sunflower production in the United States. The long-term goal of this project is to manage fungicide resistance in Diaporthe, educate farmers on using integrated approaches that combine host resistance and foliar fungicides with multiple modes of action, and develop Extension tools to increase confidence in the management of Phomopsis stem canker. The specific objectives of this project are as follows: (1) Determine the prevalence of QoI-resistant strains of D. helianthi and D. gulyae causing Phomopsis stem canker in MN, ND, NE, and SD; (2) Evaluate the effectiveness of foliar fungicides containing Succinate Dehydrogenase Inhibitor (SDHI), which is an alternative to QoIs, on Diaporthe-resistant sunflower hybrids; and (3) Enhance the knowledge and skills of farmers and agricultural professionals in managing Phomopsis stem canker through the development and dissemination of Extension tools.
Project Methods
Objective 1. Determine the prevalence of QoI-resistant strains of D. helianthi and D. gulyae causing Phomopsis stem canker in MN, ND, NE, and SD.To obtain isolates of D. helianthi and D. gulyae, a survey of commercial sunflower fields will be conducted in MN, ND, NE, and SD. Farmers, crop consultants, and NSA surveyors will assist with the survey. The number of fields surveyed will vary by state depending on sunflower production. For example, the Dakotas have more sunflower fields than MN or NE. The goal is to survey at least 50 fields each in 2024, 2025, and 2026. These fields must be at least three miles away from any previously selected field.Sampling will occur during the sunflower production months from August to October when disease symptoms are present. 10 to 20 symptomatic plants will be collected along 0.03-mile (50m) transects within each field. The transects will be randomly chosen to cover approximately 1 acre in each field. Each sample collected will be considered unique. The plants will be placed in paper bags and kept dry until pathogen isolation, which will occur within one week.To confirm the fungal identity, the diseased stems will be chopped into small pieces (2 inches or 5 cm per piece, 10 to 12 pieces). These small pieces will be disinfected with 0.5% sodium hypochlorite and 70% ethanol for one minute each. Then, they will be rinsed with autoclaved distilled water for 30 seconds and dried on autoclaved paper towels. The small stem pieces will be plated on potato dextrose agar (PDA) and incubated at 22±2°C for 10 days under 12 hours of light and dark conditions.The cultures will be examined for the presence of Diaporthe species using morphological characteristics (Mathew et al. 2015). DNA extraction will be performed on the suspected isolates, and qPCR assays specific for D. helianthi and D. gulyae (developed by Elverson et al. 2020) will be used for fungal identification.Weather data will be collected at the survey locations, including air temperature, relative humidity, and rainfall, from NDAWN (NDSU) and Mesonet (SDSU and UNL). Correlation coefficients will be calculated to determine the relationship between disease incidence and/or severity (Y) and weather variables (X), monitoring how weather variables may be linked to the increasing incidence of Phomopsis stem canker in the surveyed production areas.Objective 2: Evaluate the use of fungicides containing Succinate Dehydrogenase Inhibitor, SDHI (as an alternative to QoIs) on Diaporthe-resistant sunflower hybrids.A total of 8 to 10 locations will be established across four states over a three-year period (2024, 2025, 2026). The study design will be a randomized complete block (RCBD) with multiple fungicide treatments in at least four replicate blocks. The experimental plots will be planted with 4 rows, spaced 30 inches apart and 20 to 30 feet long, using a four-row planter at a rate of 20,000 to 22,000 seeds per acre. These trials will use sunflower varieties (partially resistant and susceptible) as the whole plot and fungicide treatments as the subplot. All trials will include the following treatments for each hybrid type: non-treated control (NTC), pyraclostrobin (R1) sprayed at 6 fluid ounces per acre, pyraclostrobin (R1) at 6 fluid ounces per acre + tebuconazole + fluopyram (R6) at 9 fluid ounces per acre, pyraclostrobin (R6) at 6 fluid ounces per acre + tebuconazole + fluopyram (R1) at 9 fluid ounces per acre. The decision to limit the fungicide treatments to four on each of the four hybrids (1 susceptible, 3 resistant) was based on the greater yield compared to the non-treated control in the Mathew et al. (2023) study (Figure 6). Weather variables will be monitored at all locations using NDAWN and Mesonet. Yield data will be collected at the end of the season at all locations.After flowering (R5 growth stage) at each location, a total of 10 plants will be used to assess disease incidence (the number of plants with stem lesions produced by the Diaporthe species, Figure 8) and disease severity in each plot. Disease severity will be assessed using a 0 to 5 disease rating scale, where 0 represents no lesions and 5 represents dead plants (Mathew et al. 2015).In addition to disease data, we will calculate the risk analyses associated with foliar fungicide application using the methodology described by Dangal et al. (2023). While keeping all production costs constant (excluding fungicide cost and sunflower seeds), we will estimate the break-even yield (the yield increase needed to cover the cost of fungicide use) for various fungicide costs and sunflower grain prices. The probability of the yield response to foliar fungicides will be estimated as p = × 100; where φ (•) is calculated as the cumulative standard-normal function, C is a constant calculated when the estimated yield and the fungicide costs are the same, is determined by calculating the yield differences between fungicide-treated and non-treated control plots, and is the standard deviation.Objective 3: Improve the confidence of farmers and agricultural professionals in managing Phomopsis stem canker by developing and educating them with Extension tools.We will develop Extension educational materials for farmers and other professionals as we complete each year's research objectives and film diagnostic materials (such as videos). Our focus will be on four main areas. First, we will look at the prevalence of QoI-resistant fungal strains in MN, ND, NE, and SD. Second, we will examine when and why foliar fungicides should be applied, specifically at field sites with a history of Phomopsis stem canker and conditions that promote disease development, to minimize unnecessary and repeated fungicide applications. Third, we will provide information on what to expect when applying a fungicide, including efficacy and economic expectations, as well as tips on preventing, mitigating, and slowing fungicide resistance by alternating the use of QoIs with fungicide products containing SDHI. Finally, we will focus on increasing farmers' and other sunflower professionals' confidence in identifying sunflower stem diseases.To achieve these goals, we plan to create at least two 3-minute videos that showcase areas where Phomopsis stem canker is occurring and being managed. We will work closely with the NSA to host these videos in their growers' section and leverage their marketing power (e-newsletter, magazine, website) to drive traffic to the new diagnostic videos. We will also collaborate with other partners/entities such as SDOC, MOC, and university Extension mechanisms to disseminate the information to growers through email alerts, links, winter meetings, state-specific Crop Pest Alerts, and more.Additionally, we will develop and distribute print materials that are either multi-state or state-specific. These materials will be developed in collaboration with our universities and stakeholders such as the NSA, agrochemical companies, and seed companies. We also plan to seek feedback and advice from stakeholders at least once a year, although our target is twice a year, to ensure that the materials we develop best meet their needs. We will specifically seek feedback from stakeholders at the NSA Research Forum held every January, and whenever possible, we will make visits to the NSA stakeholders at their annual Summer Seminar in June (location varies).