Friday, August 15, 2014

Soybean Disease Update from Steve Koenning

Physiological Scorch – Is it SDS, Stem Canker, Black Root Rot (CBR), Brown Stem Rot, or something else? 
We are receiving soybean samples in the Plant Disease and Insect Clinic (PDIC) that have symptoms of Physiological Scorch (Figure 1).  Most of the scorch in these samples is due to SDS or Sudden Death Syndrome, but numerous diseases can cause similar symptoms.  Regardless of the cause, this symptom is indicative of a problem with the vascular system once soybean has shifted to the reproductive phase.  Usually “Scorch” is the result of a root-rot such as SDS, CBR, dectes stem borer, or Phytophthora root rot.  Fungicide sprays will not impact these problems at all and should be avoided. Below are links to disease notes that will explain how to differentiate these diseases and what action to take in the future. 

Physiological scorch symptoms

Frogeye leaf spot, Target spot, and Stem Canker

Target spot of soybean and frogeye leaf spot have both been identified in North Carolina this year. Many cultivars are resistant to these diseases so there is no cause for alarm at this time.  If the disease is detected, a fungicide should be applied.  If target spot is identified, it warrants an application of a strobilurin fungicide.  If frogeye is identified, then a combination fungicide (StrategoYLD, Fortix, Quadris Top, or Affiance) may be warranted since resistance to strobilurin fungicides was identified last year in Beaufort County. See the North Carolina Agricultural Chemicals Manual for more information.  

Soybean Stem Canker has been found in the Piedmont and in Martin County.  Soybean stem canker must be controlled with varietal resistance. Fungicides rarely impact this disease, especially at this point in the season.

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