Brown Stem Rot and Sudden Death Syndrome: Are These Stealthy and Damaging Soybean Diseases Coming to a Field Near You?

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1 Brown Stem Rot and Sudden Death Syndrome: Are These Stealthy and Damaging Soybean Diseases Coming to a Field Near You? Dean Malvick Department of Plant Pathology University of Minnesota, St. Paul dmalvick@umn.edu

2 Brown Stem Rot (BSR) D. Malvick > Common & damaging in many areas of the North Central U.S. and Canada > Can be a hidden disease that is easily missed > First identified in central IL (near Cisco) in 1940 s

3 Significance of BSR BSR can be an important yield-reducing disease when conditions are favorable, and can decrease yields by reducing seed size and number BSR can cause yield losses exceeding 30%, but yield losses in the 10 20% range are likely more common This may be an underrecognized and undermanaged disease in Minnesota and North Dakota? 3

4 Brown Stem Rot Common in many years, but often unrecognized due to somewhat hidden symptoms Still important, but not as splashy as many other diseases such as SDS ( Peking example ) Managed with resistance and crop rotation This disease is most significant in the north Midwestern U.S.

5 Brown Stem Rot - Symptoms Symptoms usually develop after pods begin to fill - in mid August Vary depending on type of pathogen, environment, and soybean variety Become more severe as plants mature Wilting, premature defoliation, and lodging can develop 5

6 Symptoms of BSR Often the only symptoms are the internal stem symptoms 6

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8 BSR: Stem Browning but No Foliar Symptoms 8

9 Management of BSR Rotate crops - out of soybean (for example: at least 2 years out of soybean with corn or small grains as rotational crops) Plant soybean varieties resistant to BSR Take steps to enhance decay of soybean residue (some tillage may be beneficial) Manage soybean cyst nematode (Note: SCN can interact with BSR to increase severity of BSR) 9

10 Crop Rotation Effect on BSR. Right side - continuous soybean. 10

11 Brown Stem Rot: Management with Resistance D. Malvick, U. of Minnesota W. Pedersen

12 Sudden Death Syndrome (SDS) Counties with SDS confirmed in 2006 and 2007

13 SDS Symptoms At Different Stages Of Development On Soybean Leaves D. Malvick University of Minnesota

14 Brown/gray discoloration just under surface of lower stem, but pith remains white with SDS D. Malvick University of Minnesota

15 SDS Damage to Pinto Bean and Alfalfa Research results from Tammy Kolander, previous Graduate Student, U. of Minnesota Top photos pinto bean, bottom photos - alfalfa

16 Confirmed Distribution of SDS in Minnesota ~ 37 counties with confirmed SDS

17 Importance of SDS Soybean yield losses from SDS: 5% to >50% Losses depend on when plants are infected, weather, SCN, soybean variety. Early infections can result in pod abortion. SDS often is often severe in well-managed soybean fields with a high yield potential

18 Impact of SDS on Yield (In a Field with Low SCN) 70.0 Effect of SDS on Yield (bu/ac) of an SDS-Susceptible Variety Malvick data from Waseca, MN 2010 (based on 6 reps for each) Plots without SDS Plots with SDS Seed wt/200 seeds: 32.5 g 30.5 g

19 SDS Risk Factors Presence of SDS pathogen & field history of SDS Cool and wet soil 2-3 weeks after planting Compacted soil, poor drainage High SCN populations Susceptible soybean varieties Periodic heavy rain through mid-july followed by normal or greater rainfall through mid August

20 Scouting for SDS When: begin looking first week of August Where: usually but not always initially appears in low, poorly-drained, or compacted areas What to look for: look for yellow, diffuse spots on leaves that usually appear first in mid-canopy

21 Management of SDS Crop Rotation not effective Tillage not effective/no consistent effect Resistant Varieties EFFECTIVE Fungicides products that can suppress SDS are now available as seed treatments

22 Seed Treatments with SDS Activity Heads-Up from Plant Protectants, Inc. ILeVO from Bayer Crop Science Mertect 340-F from Syngenta (thiabendazole at new high rate)

23 BSR vs. SDS SIMILARITIES AND DIFFERENCES

24 Symptoms Sudden Death Syndrome (SDS) vs. Brown Stem Rot (BSR) SDS BSR D. Malvick D. Malvick No browning of pith in stems D. Malvick D. Malvick

25 BSR and SDS: Similarities BSR Soilborne fungal pathogen Infects roots early in summer Produces plant toxin Increased by SCN Most symptoms appear in Aug. Causes interveinal chlorosis SDS Soilborne fungal pathogen Infects roots early in summer Produces plant toxin Increased by SCN Most symptoms appear in Aug. Causes interveinal chlorosis

26 BSR and SDS: Differences BSR Widespread in MN Doesn t cause root rot Narrow host range Relatively short survival in soil Rotation effective for mgmt. Favored by wet then dry soil Common yield loss 10-15% Resistance single genes SDS Scattered but spreading in MN Causes root rot Wide host range Survives long in soil Rotation NOT effective for mgmt. Favored by wet soil into mid July Yield loss up to ~50% Resistance is complex, many minor genes

27 Final Points: BSR and SDS BSR and SDS are important and widespread diseases in the Midwest BSR symptoms often not visible on leaves Manage BSR with crop rotation and resistant soybean varieties Learn to recognize SDS (and BSR) and get proper diagnosis SDS and BSR may often be associated with SCN SDS heavily influenced by weather SDS management partially resistant varieties, manage SCN, seed treatments?

28 Questions or comments? Thanks for the financial support for research and tech transfer provided by the Minnesota Soybean Research and Promotion Council D. Malvick University of Minnesota