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📈 Diseases of Maize

Diseases of Maize.

Maize (Zea mays) is the third most important cereal crop globally. It is susceptible to numerous fungal, bacterial, and viral diseases that affect leaves, stalks, ears, and kernels. This lecture covers the major diseases of maize in India and their management.

Turcicum Leaf Blight (Northern Corn Leaf Blight)

Causal Organism

Exserohilum turcicum (syn. Helminthosporium turcicum)

Symptoms

  • Long, elliptical, greyish-green to tan cigar-shaped lesions (5-25 cm) on leaves
  • Lesions start on lower leaves and progress upward
  • Severe infection causes premature drying and significant yield loss

Favorable Conditions

  • Moderate temperature (18-27 degrees C), high humidity, heavy dew

Management

  • Grow resistant hybrids carrying Ht genes (Ht1, Ht2, Ht3)
  • Foliar spray of Mancozeb 75 WP (0.25%) or Zineb at disease onset
  • Destroy crop debris after harvest

Maydis Leaf Blight (Southern Corn Leaf Blight)

Causal Organism

Bipolaris maydis (syn. Helminthosporium maydis)

Symptoms

  • Small, rectangular tan to brown lesions restricted by veins — smaller than Turcicum blight
  • Lesions are parallel-sided and develop on all leaves
  • Race T attacks T-cytoplasm maize causing severe ear rot

Favorable Conditions

  • Warm and humid conditions (20-32 degrees C)
  • Prolonged periods of leaf wetness

Management

  • Use resistant germplasm with normal cytoplasm
  • Spray Mancozeb or Propiconazole at disease initiation
  • Crop rotation with non-cereal crops

Downy Mildew (Sorghum Downy Mildew / Crazy Top)

Causal Organism

  • Peronosclerospora sorghi — Sorghum downy mildew
  • Sclerophthora macrospora — Crazy top

Symptoms

Disease Symptoms
Sorghum DM Chlorotic streaks on leaves, excessive tillering, leafy structures replacing ears
Crazy top Proliferation of floral parts into leafy twisted structures; tassels become bushy

Favorable Conditions

  • Warm temperatures (25-30 degrees C), high soil moisture, waterlogging

Management

  • Seed treatment with Metalaxyl 35 SD (6 g/kg seed)
  • Avoid waterlogged conditions
  • Rogue out systemically infected plants
  • Spray Metalaxyl + Mancozeb combination

Post-Flowering Stalk Rot Complex

Causal Organisms

  • Fusarium verticillioides — Fusarium stalk rot
  • Macrophomina phaseolina — Charcoal rot
  • Pythium spp. — Pythium stalk rot

Symptoms

  • Plants wilt suddenly after tasseling or grain filling
  • Internal stalk tissue becomes soft, discoloured, and shredded
  • Charcoal rot: Stalk pith is filled with minute black sclerotia
  • Fusarium rot: Pink to salmon-coloured fungal growth on stalk nodes

Favorable Conditions

  • Drought stress followed by warm temperatures
  • Poor soil fertility, high plant populations

Management

  • Balanced fertilization, especially potassium
  • Avoid moisture stress during grain filling
  • Grow tolerant hybrids
  • Harvest early to reduce stalk-rot losses

Ear Rot and Mycotoxin Concerns

Maize ears are affected by several fungi that produce dangerous mycotoxins:

  • Aspergillus flavus — Produces aflatoxins (carcinogenic)
  • Fusarium verticillioides — Produces fumonisins (linked to esophageal cancer)

Management

  • Timely harvest at proper moisture content
  • Proper drying and storage of grain
  • Biocontrol using atoxigenic strains of A. flavus

Summary Cheat Sheet

Disease Typical sign Core management
Turcicum leaf blight Long elliptical blight lesions Resistant hybrids + timely fungicide
Maydis leaf blight Smaller elongated brown lesions Seed treatment + foliar protection
Downy mildew Chlorotic striping and downy growth Seed treatment + rogueing

References

1 source

- ICAR maize pathology extension notes. - Agrios GN. Plant Pathology. 5th ed. - BSc Agriculture disease-management manuals.

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