Biology and Management of Black Dot of Potato

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1 Biology and Management of Black Dot of Potato Neil C Gudmestad University Distinguished Professor & Endowed Chair of Potato Pathology Department of Plant Pathology North Dakota State University

2 Black Dot of Potato Caused y Colletotrichum coccodes, a seed and soil orne pathogen. The lack dot pathogen attacks all major parts of the potato plant; leaves, aove and elow ground stems, roots, and tuers. Gloally it is known primarily as a lemish disease. Name derived from the small sclerotia that form on infected plant parts, i.e., lack dots. The pathogen resists the action of metam sodium so soil fumigation with this chemistry is relatively ineffective.

3 D. Johnson, WSU

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8 C. coccodes / stem (%) Black Dot Source of Inoculum/Site of Infection Non inoculated/infested Browerville, MN 2003 Aove Ground Stem Below Ground Stem Root Stolon Pasche, et al Days after emergence

9 Black Dot Source of Inoculum/Site of Infection Non inoculated/infested Browerville, MN 100 Black dot stem incidence 119 DAP C. Coccodes / stem (%) Black dot stem incidence 117 DAP ~69 ppg <1 ppg Pasche, et al Days after emergence

10 Aove ground stem incidence (8 22) Black dot source of inoculum / site of infection Browerville, MN 2003 R 2 = 0.77; P = Pasche, et al Total yield (cwt/a)

11 6 Black dot source of inoculum / site of infection Browerville, MN 2004 Aove ground stem incidence (8 22) R 2 = 0.18; P = Pasche, et al Total yield (cwt/a)

12 Impacts of Black Dot on Quality

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15 Black Dot Management

16 Soil Quantification of Black Dot

17 Duplex qpcr for C. coccodes sclerotia and External control (M13) added to soil to determine efficiency of DNA

18 40 Standard Curve used for quantification of C. coccodes sclerotia in qpcr Threshhold Cycle (Cq) y = x R² = Log of Cc sclerotia level

19 Results from soils tested for C. coccodes (Cc) in Sample Id and Location.. Total numer of samples tested Level of Cc sclerotia Negative Very Low Low Mod. High Farm 1, NE Farm 2, NE Farm 3, CO 2 2 Farm 4, CA Farm 5, ME Farm 6, WI Farm 7, WA >10 5 sclerotia/g corresponds to high pathogen count; moderate; low; 1 10 very low.

20 Black Dot Chemical & Biological Control

21 Black Dot Efficacy Inkster, ND 2013 a High Black Dot Disease Pressure Year!!! RAUDPC Gudmestad, et al SASO 2 qt/emesto SASO 2 qt/emesto Non Trt Serenade ASO Serenade S 4 qt SS 2qt/Emesto Prime 0.4oz IF IF SS 2 Prime qt/vellum oz IF 4 qt/a IF Treatment

22 Black Dot Efficacy Inkster, ND 2014 a RAUDPC d c Gudmestad, et al Non Trt Serenade ASO 2 qt IF/ Quadris IF Serenade ASO 2 qt IF Non Trt SS IF/Reason Quadris IF Serenade S 2 qt Reason 1,3 Treatment

23 Black Dot Efficacy Inkster, ND 2016 a RAUDPC Gudmestad, et al Non Trt Reason 1,3 Vellum IF Headline 1,3 Vellum/Ser Headine 1,3 Treatment

24 a Black Dot Efficacy Inkster 2017 RAUDPC Non-treated Quadris- IF + 1 F Elatus IF + 1Q,F Reason + Luna T 1, 5 Vellum P IF + R 1, F Serenade IF + 1 R, F

25 Total Yield Black Dot Treatments Inkster a a Cwt/a Non-treated Quadris- IF + 1 F Elatus IF + 1Q,F Reason + Luna T 1, 5 Vellum P IF + R 1, F Serenade IF + 1 R, F

26 Summary The lack dot pathogen attacks all major parts of the potato plant; leaves, aove and elow ground stems, roots, and tuers. The three most economically important phases of lack dot are the tuer lemish phase, root rot phase, and its role in the early dying complex. Pathogen infection appears to occur early in plant development. QoI and SDHI fungicides can provide control of aove and elow ground phases of the lack dot disease complex. Using qpcr to quantify the level of lack dot in soil can assist in management decisions.

27 BD Treatment Recommendations QoI (stroilurin) recommendations: Quadris, Headline, Reason, Priaxor all have activity, highest disease control when applied efore row closure at mid rates. SDHI recommendations: Luna T, Elatus, Priaxor and Vertisan all have activity. Endura does not. All of these SDHI fungicides can e used prior to row closure as you would use stroilurins. Luna (Vellum Prime) can e used also in furrow at planting, provide longer residual control than stroilurins. Serenade Soil at 2 4 qt/a applied IF appears to e a viale iological option.

28 Thank you! Questions?