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Northern Leaf Blight

 
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Northern Corn Leaf Blight

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Symptoms

Corn leaf with early lesion of northern leaf blight
 

Symptoms - Early

  • Early northern corn leaf blight lesions are gray-green and elliptical, beginning 1 to 2 weeks after infection.
  • In a susceptible reaction, fungal sporulation will begin within a few days.
Developing lesions of northern corn leaf blight
 

Symptoms - Fully Developed

  • Northern corn leaf blight lesions become pale gray to tan as they enlarge to 1 to 6 inches or longer.
  • Distinct cigar-shaped lesions unrestricted by leaf veins make northern corn leaf blight (NCLB) one of the easiest diseases to identify.
  • Under moist conditions, lesions produce dark gray spores, usually on the lower leaf surface, giving the lesions a "dirty" appearance.
  • As many lesions enlarge and coalesce, entire leaves or leaf areas may be covered.
  • Heavy blighting and lesion coalescence give leaves a gray/burned appearance.

Facts

  • Caused by Exserohilum turcicum (previously classified as Helminthosporium turcicum), a fungus found in humid climates wherever corn is grown.
  • Survives in corn debris and builds up over time in high-residue and continuous corn cropping systems.
  • Favored by heavy dews, frequent showers, high humidity and moderate temperatures.
  • Spores are spread by rain splash and air currents to the leaves of new crop plants in spring and early summer. Spores may be carried long distances by the wind.
  • Infection occurs when free water is present on the leaf surface for 6 to 18 hours and temperatures are 65 to 80 F.
  • Infections generally begin on lower leaves and progress up the plant, but infections may begin in the upper plant canopy when spore loads are high.
  • New NCLB lesions can produce spores in as little as 1 week, allowing NCLB to spread much faster than many other corn leaf diseases.

Disease Cycle

Northern corn leaf blight disease cycle
 

Impact on Crop

Field showing northern corn leaf blight damage
Field showing northern corn leaf blight damage
 
  • Infections by NCLB can occur at any growth stage, but plants are more susceptible after pollination.
  • Yield losses may be caused by:
    • decreased photosynthesis resulting in limited ear fill
    • harvest losses if secondary stalk rot infection and stalk lodging accompany loss of leaf area.
  • Yield losses are most severe when NCLB infects corn plants early and progresses to the upper plant leaves by pollination or early ear fill.
  • If ear development outpaces disease progression, yield losses will be lower.

Hybrid Selection

  • Pioneer researchers select for resistant parent lines and hybrids in multiple environments where NCLB pressure is consistently high year after year.
  • Pioneer hybrids are rated for NCLB resistance and ratings made available to customers.
  • Most hybrids are rated from "3" to "6" on Pioneer's 1 to 9 scale, where 9 indicates highly resistant.
  • Growers should choose hybrids rated a "5" or "6" for fields at risk of NCLB infection.
  • 2 types of resistance are available in hybrids:
Multigenic ResistanceSingle Gene Resistance
non-race-specific race-specific ("Ht" Resistance)
more stable over time may be overcome in time ("Ht" Resistance)
reduces number of lesions on a leaf delays spore production, limits sporulation ("Ht" Resistance)
 
HT lesion type: A chlorotic region may surround the lesion
 

Management

  • Crop rotation to reduce previous corn residues and disease inoculum
  • Tillage to help break down crop debris and reduce inoculum load
  • Fungicide application to reduce yield loss and improve harvestability
  • Consider hybrid susceptibility, previous crop, tillage, field history, application cost, corn price

Corn foliar fungicides and efficacy against NCLB. Adapted from Wise, 2014.

FungicideActive IngredientsChemical GroupNCLB Efficacy
Aproach® picoxystrobin methoxy-acrylates very good
Aproach
Prima
picoxystrobin + cyproconazole methoxy-acrylates & triazoles very good
Domark® tetraconazole triazoles no data
Headline®
AMP
pyraclostrobin + metconazole methoxy-carbamates & triazoles very good
Headline® EC
Headline® SC
pyraclostrobin methoxy-carbamates very good
Quadris® azoxystrobin methoxy-acrylates good
Quilt®
Quilt® Xcel
propiconazole & azoxystrobin triazoles & methoxya-crylates very good
Stratego® YLD prothioconazole & trifloxystrobin triazoles & oximino-acetates very good
Tilt® propiconazole triazoles good

Wise, K. 2015. Fungicide efficacy for control of corn diseases. Purdue Extension Publication BP-160-W.
Purdue University, West Lafayette, Indiana.

Pioneer® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents. Product responses are variable and subject to a variety of environmental, disease and pest pressures. Individual results may vary. Fungicide performance is variable and subject to a variety of environmental and disease pressures. Individual results may vary. Always read and follow all label directions and precautions for use when applying fungicides. Labels contain important precautions, directions for use and product warranty and liability limitations that must be read before using the product. Mention of a product does not imply a recommendation.

 
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