Proposal Objective and Goal Statements:
1) A New Approach to Managing White Mold in MN Soybean. (PI: A. Peltier, Cooperator: D. Malvick)
a) Conduct irrigated, inoculated field trials to compare coverage and efficacy of fungicides applied both between the rows and within the canopy (experimental) to typical over-the-top (standard) of the canopy.
b) Assess disease incidence and severity and soybean yield and moisture for plots treated with fungicide applied over the top of the canopy (standard) or within the canopy (experimental).
2) Expanding Digital Crop Doc, a digital diagnostics service (PI: A. Peltier in cooperation with UMN Extension communications and crops personnel). a) Work to advertise and promote the UMN digital disease diagnostics program, Digital Crop Doc, to make sure that more MN soybean farmers are aware of and use this service. b) Coordinate a team of ten Univ. of Minnesota Extension ‘diagnosticians’ to provide preliminary diagnoses and management recommendations to Digital Crop Doc submitters.
Objective 1: A New Approach to Managing White Mold in MN Soybean.
The problem. White mold is an economically important disease caused by a soil-borne fungus called Sclerotinia sclerotiorum. The pathogen has a very wide host range including soybean, dry edible bean, sunflower, canola, sugar beet, peas and snapbeans (Boland and Hall 1994), crops of economic importance to Minnesota. In soybean, spores land on and colonize senescing soybean flowers that remain attached to the plant at leaf axils. The fungus uses this food source to infect the stem.
Disease is favored by cool to moderate maximum daily temperatures and moisture from rain, fog, dew or high relative humidity and a dense canopy during the beginning flowering through beginning pod growth stages. Many of the production practices that have been adopted to maximize yield potential such as early planting, narrow row widths, high plant populations and high soil fertility tend to favor a dense canopy and therefore also favor white mold (Peltier et al. 2013). From 1996 through 2019, annual yield losses in Minnesota soybean due to white mold were estimated to be as high as 3.2 percent, with up to 13.3 million bushels lost; disease losses were as high as $14.8 per acre and $120.2 million total (Crop Protection Network, 2019).
Current management challenges. There are no methods to completely control white mold. This is true even should one adopt the currently recommended integrated approach to management (Peltier et al. 2013). Consequently, even with active, integrated management, yield losses can be significant in growing seasons that favor white mold.
The periodic nature of disease suggests that a fungicide applied only in those years in which disease is favored might be both economical and highly effective. Fungicides labeled for white mold act in a protectant rather than curative fashion. Consequently, timing a foliar fungicide application to occur at the beginning flowering (R1/R2) growth stage is important so that it is in place prior to pathogen colonization. However, significant yield losses can occur even when fungicide applications are perfectly timed. This is likely due to inadequate canopy penetration and coverage by the fungicide at the site of infection.
Proposed novel solution. An Illinois company developed sprayer nozzle body units that attach to the Y-DropTM riser tubes typically used for side-dress nitrogen applications. From a white mold management perspective, systems like this in which multiple nozzles ride within the canopy and between rows are likely to improve canopy penetration and fungicide coverage to provide better protection from the pathogen and maintain yield potential.
To compare standard fungicide applications to those applied using the between-the-row, within-the-canopy spray system custom built tool bars were fabricated to be bolted to a small tractor-mounted sprayer housed at the Northwestern Research and Education Center in Crookston
(Figure 1). These tool bars are capable of either applying fungicides as typically applied in soybean, over-the-top of the canopy with flat fan nozzles, or applying fungicides with multiple nozzles riding between 22 or 30 inch soybean rows and within-the- canopy, approximately 12 inches from the soil line. For the within-the-canopy units, chemical-resistant hose, plumbing and sprayer fixtures and junctions were used to fashion the body onto which to affix the nozzle filters and nozzles. Zip ties were used to connect the nozzle body onto the bottom of a square, hollow, steel pipe that would ride within the canopy and between rows. Plastic skid plates were bent and riveted to the steel pipe so that the nozzle body could easily glide through the canopy, minimizing potential plant injury. Two of the nozzles faced either rows applying fungicide with flat fan nozzles oriented vertically to stem tissue and one rode at a 45° angle with a flat fan oriented horizontally, facing up and under the canopy.
Figure 1. Configuration of the tractor-mounted hydraulic-powered plot sprayer used to apply fungicides in this experiment. Note that two different within-the-canopy booms were built to allow application down the center of both 22 (Crookston study site) and 30 inch (Staples study site)-spaced soybean rows. The within-the-canopy nozzle body (black circle/square) rode approximately 12“ from the soil surface and the over-the-top nozzles (white circle/square) rode approximately 8“ above the soybean canopy.
In order to provide a ‘good disease environment in which to compare efficacy of fungicide applied using within-the-canopy and typical flat fan systems, two field trials will be conducted in 2021 in disease nurseries. Briefly, high seeding rates of locally adapted, white mold susceptible soybean varieties will be planted into irrigated fields. At beginning flower (R1) when rows are filling, fungicides will be applied to some plots in the traditional method: over the top of the canopy, using flat-fan nozzles that produce course to very course droplets (as recommended on some fungicide labels to ensure canopy penetration). Fungicides will be applied to other plots using the within-the-canopy sprayer system and nozzles will apply medium sized droplets (Table 1). To introduce inoculum once the fungicide has dried on the plants, 1 liter of dried sorghum seed that had been previously infested with S. sclerotiorum will be spread onto plots. Fungicide treatments will be randomly assigned to plots in a randomized complete block design with six replicates. Treatments include: 1. uninfested unsprayed (- control); 2. Infested, untreated control (+ control), 3. Infested, fungicide applied over-the-top of the canopy with flat
fan nozzles, 4. Infested, fungicide applied within the canopy, between the rows with three flat fan nozzles.
Table 1. Details regarding the nozzle type and details, spray volume, speed, pressure and droplet size of fungicides applied over the top of the canopy and within the canopy. See Figure 1 for a picture of what both look like.
Similar to the protocols detailed in Ferguson et al (2016), prior to fungicide treatment, 2 x 3” water sensitive paper (WSP) will be affixed to metal stakes in the mid- and lower-canopy in each plot fungicide plot. WSP will be collected after treatments are applied and then analyzed to estimate spray coverage at each canopy position in each plot. Figure 2 is scans of WSP from the 2020 white mold experiments funded by MSRPC.
Figure 2. Water sensitive paper that had been placed 6 inches above the soil line in the soybean row before fungicide was applied in 2020 using either the traditional over-the-top method (left) or the experimental within-the-canopy method (right). A document scanner and the Deposit Scan software was used to impartially assess spray coverage and fungicide deposition. Note that darker areas indicate where fungicide droplets fell on the water sensitive paper.
At the full pod growth stage (R6), thirty plants from a representative section of each plot will be assessed for disease incidence and severity according to Grau et al. (1982). Briefly, plants will be rated on a 0 to 3 scale. Plants with a score of 0 have no symptoms, plants with a score of 1 have lesions on only lateral branches, plants with a score of 2 have lesions on the main stem, but there is both no wilt and normal pod development and plants with a score of 3 have lesions on main stem resulting in plant death and poor pod fill. A disease severity index (DSI) will then be calculated for each field plot using the following formula: DSI = 100 x S x/yz, in which x is the ratings, y is the maximum rating, and z is the number of
plants rated. Plots will be harvested for soybean yield and moisture. Funds are requested from MSR&PC to cover supplies, personnel and plot and travel costs associated with these white mold experiments.
Objective 2: Expanding Digital Crop Doc, a digital diagnostics service.
Extension continues to work to develop new ways to continue to identify critical IPM-related management challenges and to respond in a timely fashion to such challenges by providing research-based management recommendations to crop producers. With funding provided by the Minnesota Soybean Research & Promotion Council, in 2020 UMN Extension developed a website called “Digital Crop Doc”. On this website, agricultural professionals can submit up to 10 digital photos and context clues to aid in diagnosing crop plants. As soon as there is a submission, UMN Extension diagnostics personnel are notified and have three business days in which to provide a diagnosis and management recommendations to the submitter. UMN Extension communications personnel maintain the website and a submission database, follow up with diagnosticians to ensure timely follow up with the submitter and data entry into an internal database. The maintenance of this internal database is essential for UMN Extension personnel to be alerted to the need to communicate regarding an important emerging disease threat, particularly for those diseases for which in-season management options are available.
To improve the reach of this in-person-contactless service, communications personnel will work to more widely advertise this program to MN soybean producers. A more widely used program would better help determine pressing needs for both disease and pest management research and education among the larger community of agricultural professionals. Educational needs could be met through in-person or Zoom-mediated programs, or through regional or statewide Extension newsletters like NW Cropping Issues (regional) and MN Crop News (state-wide).
In 2021, we propose to staff the behind-the-scenes diagnostics work associated with the Digital Crop Doc website for five full months, from May 1 through September 30. We are requesting funds to cover advertising (May/June issue of “Soybean Business” and two weeks of digital advertisement in “Minneline”), two weeks of salary and fringe costs for Phyllis Bongard, the UMN Extension communications specialist who makes digital crop doc run, and half the cost of a software license with which to manage the database. We are also seeking funding from the Minnesota Corn Research & Promotion Council to fund Digital Crop Doc.