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Identification and Management of Soybean Diseases Anthony Muhle Prepared by Nicholas Arneson and Loren Giesler University of Nebraska-Lincoln Institute of Agriculture and Natural Resources

Soybean Seedling Diseases Pythium damping-off and root rot Fusarium root rot Rhizoctonia cortical and root rot Phytophthora root and stem rot

Diseases/Disorders Cause Cotyledon Injury Pythium seedling blight Pre-emergence herbicide injury

Conditions for disease development Soil moisture Soil temperature Pythium Flooded Cool (50-60 F) Phytophthora Flooded Warm (70s F) Fusarium Wet to dry Cool to warm Rhizoctonia Damp to wet Warm (70-80s F)

Management of Seedling Diseases Plant high quality seed Improve soil drainage by tiling fields that often have excessive water Use seed applied fungicides Know the field history Match chemistry to the disease Combination products

Phytophthora Management Resistant varieties: specific race resistance and tolerance (most rated to Race 25) 1C or 1K Over 65 races of pathogen exist Fungicides (metalaxyl and mefenoxam) require increased rates ; ethaboxam Improve field drainage

Soybean Cyst Nematode (SCN)

Distribution of SCN in Nebraska (Jan-2018) As of January 1, 2018 SCN identified in 59 Nebraska counties producing over 92% of Nebraska s soybeans!

SCN Nodule

Year 1 PI 88788 SCN-resistant soybean Year 6 Nonhost crop Year 2 Nonhost Crop Recommended rotation for fields with SCN infestations Year 5 SCN-resistant soybean Year 5: rotate to other source of SCN resistance. Year 3 Peking SCN-resistant soybean Year 4 Nonhost crop

UNL SCN RESEARCH 2006-2014 Ave. yield: 32 infested sites Resistant varieties: 55.9 bu/a Susceptible varieties: 51.3 bu/a Ave. yield: 12 non-infested sites Resistant varieties: 59.5 bu/a Susceptible varieties: 62.9 bu/a

SOIL SAMPLING (Use your check off: Free SCN Assays are available) Soil sampling is the first step to determine if you have SCN or not. This program will be active again in 2018.

Sudden Death Syndrome (SDS) Symptoms at top of the plant first Pockets in fields

Conditions that can affect SDS 1. Soil moisture 2. Temperatures 3. Soil compaction 4. Soybean cyst nematode

Sudden Death Syndrome Varieties vary in their susceptibility to SDS

Brown Stem Rot SDS Pith turns brown and forms into disks Pith remains white Vascular system stays white Vascular system turns a bluish-gray to brown color. Typically more distinct at the crown

Soil borne fungal pathogen Survives as sclerotia White Mold Practices that increase yield encourage disease development Favored by cool, cloudy, wet weather at flowering Wilting in canopy followed by watersoaked spots

White Mold Management Partial genetic resistance available Crop rotation only partially effective Fungicides at R1-R2 Efficacy decreases once symptoms appear Reduce irrigation at flowering Sanitation Clean equipment Harvest fields last to reduce spread

Fungicide Comparison Field Trial for White Mold Scribner, NE 2017 Causal agent: Sclerotinia sclerotiorum Infects senescing flowers ~ R1 stage Produces sclerotia for survival inoculum Field Trial Scribner, NE Evaluated 4 registered fungicides Plot incidence of white mold (%) Grain yield (bu/acre) RCBD, 4 plot replications Plots were 10 ft wide (4 rows), 25 ft long Fungicides applied at R1 and R3 15 gal/acre

Results from Fungicide Comparison Field Trial for White Mold Scribner, NE 2017 Table 1: White mold incidences (%), area under the disease progress curve (AUDPC) scores, and yield (bu/acre) Product Rating 1: Rating 2: (active ingredient) -Rate zy 28 DAA x 42 DAA Rating 3: 49 DAA AUDPC Yield (bu/acre) Control 7.9 w a v 18.6 a 22.6 ab 329.8 a 41.7 a Endura (boscalid) - 5.5 Proline 480 SC (prothioconazole) - 3.0 Domark 230 ME (tetraconazole) - 4.0 Topsin 4.5 FL (thiophanate-methyl) - 30.0 4.0 b 7.7 de 10.9 d 147.2 d 42.7 a 3.8 b 10.3 cde 13.5 cd 182.2 cd 43.1 a 6.1 ab 17.0 ab 22.8 a 300.5 ab 42.6 a 4.0 b 12.9 bcd 17.9 abc 226.7 bcd 45.4 a LSD (α=.10) 3.1 5.6 5.9 94.6 4.8 z rate units: FL OZ/A, except Endura: OZ WT/A y application dates: R1:7/13/17, R3:7/27/17 x DAA: days after R3 application w Disease incidence rated on 0-100% linear scale v Different letters indicate significant difference at α=.10

Performance in WI Trials (Dr. Damon Smith UW) Most consistent performing programs are as follows: 1. Single application of Endura @ 8 oz. at R1/R2 2. Aproach @ 9 fl oz. Two applications (R1 & R3) 3. Proline @ 3 fl oz at R1 followed by Stratego YLD @ 4 fl oz at R3 Cobra herbicide at R1 does well, but if white mold pressure is low, you will notice some yield loss from the Cobra injury. However, if white mold pressure is high, then Cobra ends up being a top performer.

iphone and Android App Coming Uses same models as the ipipe version Available for the U.S. and Canada Can be run in the field or at the desk Uses a combination of user inputs and GPSreferenced weather information to provide a risk of white mold so you can make a spray decision Look for it in the Apple and Android Stores in the 2018 growing season! in 2018!

Bacterial Blight Bacterial Pustule Brown Spot Downy Mildew

Frogeye Leaf Spot

Frogeye Leaf Spot Fungal disease which is residue born. More severe in no-till and continuous soybean.

Frogeye Leaf Spot Management Soybean varieties vary in their susceptibility Resistant varieties are available. Fungus overwinters in residue and will be more severe in continuous soybean and no-till. Fungicides can increase yields if applied at growth stage R3- R5. Products containing QOI fungicides.

Frogeye Leaf Spot Fungicides applied at R3-R5 growth stage. No Treatment Strobilurin Fungicide

Results of Cercospora sojina fungicide sensitivity testing (conidial germination) Baseline isolates (n = 58) 2010 TN isolates (n = 15) Fungicide EC 50 range EC 50 mean EC 50 range EC 50 mean ~1000x Azoxystrobin 0.0029 0.0323 0.0127 2.7826 4.5409 3.1644 Pyraclostrobin 0.00014 0.00076 0.00027 0.2818 0.6404 0.3297 Trifloxystrobin 0.00018 0.00311 0.0012 0.3665 2.5119 0.8573 Notes: EC 50 = effective concentration that inhibits 50% conidial germination when compared to non-amended (no fungicide) media. Unit is μg/ml. Bradley (2010): Research funded by the Illinois Soybean Promotion Board

Get Help If Uncertain About Your Diagnosis!!! Kyle Broderick, Diagnostician Plant & Pest Diagnostic Clinic Rm. 448 Plant Sciences Hall University of Nebraska Lincoln, NE 68583-0722 (402) 472-2559

Sample Submissions Do s Send several whole plants, roots and all stages of the symptoms Include normal plants Enclose the root ball in a plastic bag separate from the leaf material Place entire sample into a plastic bag Provide as much information as possible Crop growth stage Symptom distribution Description of the symptom How many plants in area affected? Mail sample Monday through Wednesday

Sample Submission DON T DON T Add water If there is excess water with the sample add dry towels to absorb the moisture DON T Leave sample on the dash of the pickup Keep samples cool. Store in a refrigerator overnight/weekend if needed DON T Place samples in paper bags (especially leaf samples) DON T Mail Thursday or Friday

The accuracy of the diagnosis is often a function of the quality of the sample collected and the thoroughness of the background information provided.

Kyle Broderick, Diagnostician @UNLPlantClinic Available on-line at: https://cropwatch.unl.edu/plantdisease/unl-diagnostic-clinic-lincoln

More Soybean and Corn Disease Resources Crop Watch - http://cropwatch.unl.edu/ Newsletter, efficacy trial data, and publications Market Journal weekly episode or see videos at: http://marketjournal.unl.edu/soybeandiseases Videos YouTube UNL CropWatch channel short Corn/Soybean Disease videos Crop Protection Network http://cropprotectionnetwork.org Tamra Jackson-Ziems - @tjcksn Loren Giesler - @MulletManLG Contact local county Extension office

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