Look Out for Gray Leaf Spot and Northern Corn Leaf Blight

Categories: GROWING, CORN
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Gray leaf spot
Gray leaf spot (GLS) is one of the biggest yield-robbing corn diseases farmers face in the U.S. GLS can rapidly increase with warm temperatures 70–90°, high humidity greater than 90% or periods of prolonged (12+ hours) leaf wetness. The likelihood of GLS increases greatly in fields with prior year corn residue that can host the pathogen, such as continuous corn crop rotations and/or minimal/no-till management.  

What to look for:
  • Infection starting in the lower canopy, progressing upward.
  • Lesions beginning as small oval, light-tan spots with circular halos.
  • Lesions typically expand into long, narrow, rectangular lesions parallel to the leaf veins and later turn gray.
  • Symptoms also can be confused with bacterial leaf streak (BLS), however, GLS has blocky/rectangular lesions, whereas BLS has wavier lesion margins.


A. Lower leaf progressing rapidly with GLS  B. Small beginning lesions with halos and expanded rectangular lesions 

Northern corn leaf blight  
Northern corn leaf blight (NCLB) is another leaf disease to protect our corn crop. This disease is caused by a fungus that overwinters as mycelium and spores in corn residue. Wind and splashing water disperse the spores. NCLB development typically occurs at or after silking, and is favored by extended periods of leaf wetness such as rain or heavy dew, and moderate temperatures of 65–80°.
What to look for:
  • Symptoms usually first appear on the lower leaves.
  • Cigar or elliptical-shaped lesions develop longitudinally with leaf veins.
  • Lesions are light green or gray in color, then soon turn tan.
  • Dark spores appear, making the leaf surface seem dirty within the lesion.
  • Severely affected plants will kill entire leaves, making it difficult to find individual lesions.

A. Early stage NCLB lesions  B. Medium stage NCLB lesions, typical cigar-shaped infection  C. Late stage NCLB lesions, when individual lesions coalesce together

Potential yield loss
Both diseases hurt yield by reducing the corn plant’s photosynthetic area, reducing carbohydrate production needed for kernel development. The reduction in photosynthetic leaf area results in carbohydrates being scavenged from the stalks, predisposing the plant to stalk rots and lodging. Early infection and conducive conditions for development can lead to significant yield losses. Table 1 illustrates the yield loss associated with varying levels of GLS infection at R5, or dent, roughly 25–30 days before reaching maturity (R6 to black layer).


During high moisture conditions conducive to pathogen development and early establishment of NCLB, yield losses can be as severe as 30–50%. However, with lower levels of infection or delayed infection (6 weeks after silking), yield losses are usually minimal.2

Management practices
Corn hybrids do have some levels of resistance to both diseases. However, there are truly no resistant or immune hybrids. Golden Harvest corn hybrids each have a specific rating for their genetic ability to handle GLS and NCLB. More information on hybrid disease tolerance is available in the product section, which should be referenced for future product placement.

Since both pathogens can overwinter, residue management also decreases future GLS and NCLB pressure. Practices that bury residue such as crop rotation and tillage can reduce spore carryover to the following year. 

​​​​​​​Fungicide applications are also effective for controlling both diseases. When lesions are present at the ear leaves 2 weeks prior to and after tasseling, using a proven product with good activity on target disease is recommended. If considering an early application to proactively prevent GLS or NCLB, spray a fungicide with preventive and curative disease control, such as Trivaprvo®, to help maximize yield and profit potential.

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights. 

Sources:

  1. Patrick Lipps, 1998, The Ohio State University. Gray leaf spot and yield losses in susceptible corn hybrids. Crop Observation and Recommendation Network. Issue 98-23.
  2. Salgado, J.D., Schoenhais, J, and Paul, P.A. 2016. Northern corn leaf blight. Ohio State Extension PLPATH-CER-10. http://ohioline.osu.edu/

Photos are eithe the property of Syngenta or used under agreement.

Syngenta hereby disclaims liability for third-party websites.


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