A) Post Flowering Stalk Rot and Cephalosporium Wilt (Black Bundle Disease and Late Wilt) in Maize

Causal Agents

• Cephalosporium acremonium
• Cephalosporium maydis

Symptoms

i) Cephalosporium acremonium

• • Stage of Appearance: Symptoms appear at the dough stage of maize.
  • Purpling of Leaves and Stalks: Initial symptoms include purpling.
  • Blackening of Vascular Bundles: Black streaks in vascular bundles, extending through several internodes.
  • Pith Shredding: Shredding of the internodal pith region.
  • Barren Plants and Excessive Tillering: Plants may appear barren with excessive tillering and multiple ears.

ii) Cephalosporium maydis

• • Stage of Appearance: Symptoms appear after the flowering stage.
  • Wilting Pattern: Plants show basipetal wilting (wilting from the base upwards).
  • Leaf Discoloration: Leaves turn dull green and eventually dry up.
  • Lower Internode Symptoms:
    • Turns reddish-brown and becomes shrunken, soft, then dry and hollow.
    • Reddish-brown vascular bundles are visible when stalks are split open.

Pathogen Characteristics

• Conidiophores: Swollen or slender.
• Conidia: One-celled, hyaline (colorless), produced successively at the tip, and embedded in a slimy drop.

Disease Cycle

• Survival: Pathogens survive in soil, plant debris, and seed.
• Dispersal: Spread occurs through contaminated soil, debris, and infected seeds.

Favourable Conditions: High Temperature and Low Soil Moisture (Drought) promote the disease.

Management

i) Cultural Practices

• • Crop Sanitation: Remove infected plant debris to reduce inoculum.
  • Crop Rotation: Avoid continuous maize cultivation to break the disease cycle.
  • Water Management: Avoid water stress, especially at the flowering stage.

ii) Seed Treatment Treat seeds with Thiram or Captan at 3 g/kg seed to prevent seed-borne infection.

iii) Resistant Varieties Use resistant cultivars such as: DHM-103, DHM-105, Hi-Starch, Ganga Safed-2

B) Downy Mildew in Maize and Other Crops

Causal Agents

1. Sorghum Downy Mildew – Peronosclerospora sorghi / P. philippinensis
2. Crazy Top Downy Mildew – Sclerophthora macrospora
3. Brown Stripe Downy Mildew – Sclerophthora rayssiae var. zeae
4. Sugarcane Downy Mildew – Peronosclerospora sacchari

Symptoms

• Chlorotic Streaks: Characteristic yellowish streaks on leaves.
• White Downy Growth: Visible on the lower leaf surface and on chlorotic streaks. Also seen on bracts of green, unopened male flowers in the tassel.
• Stunted and Bushy Appearance: Caused by shortening of internodes.
• Leaf Shredding: Affected leaves tear linearly.
• Tassel Malformation: Partial or complete transformation into a mass of narrow, twisted leafy structures.
• Crazy Top Symptoms: Proliferation of axillary buds on the stalk of tassels and cobs.

Pathogen Characteristics

• White Downy Growth: Composed of sporangiophores and sporangia.
  • Sporangiophores: Short, stout, and profusely branched with pointed sterigmata.
  • Sporangia (Conidia): Hyaline, oblong, or ovoid, which germinate directly to infect plants.
  • Oospores: Formed at advanced stages, spherical, thick-walled, and deep brown.

Favourable Conditions

• High Relative Humidity: About 90%.
• Water Logging and Light Drizzles: Favorable for disease development.
• Temperature Range: 20-25°C.
• Susceptibility: Young plants are highly susceptible.

Mode of Spread and Survival

• Primary Source: Survives in soil, plant debris, and collateral hosts (e.g., Sorghum bicolor, Sorghum halapense).
• In Punjab: Digitaria sanguinalis serves as the primary infection source.
• Secondary Spread: Through air-borne conidia.
• Oospore Survival: In soil and infected plant debris.

Management

i) Cultural Practices

1. • Destruction of Plant Debris: To reduce inoculum sources.
   • Removal of Collateral Hosts: To break the disease cycle.
   • Deep Summer Ploughing: Exposes oospores to sunlight, reducing viability.
   • Crop Rotation: Rotate with pulses to break pathogen life cycle.
2. Resistant Varieties DHM-1, DHM-103, DMR-5, and Ganaga II.
3. Seed Treatment Metalaxyl (Apron 35SD) at 4 g/kg seed.
4. Chemical Control Foliar Spray: Metalaxyl MZ (Ridomil MZ) @ 0.2%. Application Schedule: Spray 3-4 times, starting 20 days after sowing.

C) Turcicum Leaf Blight in Maize

Causal Agent: Helminthosporium turcicum (Syn: H. maydis)

Economic Importance Geographic Prevalence: Severe in Andhra Pradesh, particularly in the districts of Warangal, Karimnagar, Medak, Nizamabad, Adilabad, and Ranga Reddy.

Symptoms

• Lesions on Leaves:
  • Long, elliptical, grayish-green or tan lesions measuring 2.5 to 25 cm in length and up to 4 cm in width.
  • Initially appear as small yellowish round to oval spots, which gradually enlarge into bigger elliptical spots.
  • Color: Straw to grayish-brown centers with dark brown margins.
  • Blighted Appearance: Spots coalesce, giving a blighted look to the leaves.
  • Olive Green Velvety Masses: The lesions get covered with conidia and conidiophores.
  • Necrosis and Death: Under high humidity, the entire leaf area becomes necrotic, making the plant appear dead.
  • Extended Lesions: Can spread to husks.

Pathogen Characteristics

• Conidiophores: Occur in groups, geniculate (bent knee-like), mid dark brown, and become pale near the apex. Smooth surface.
• Conidia: Distinctly curved and fusiform (spindle-shaped). Pale to golden brown with 5-11 pseudosepta.

Disease Cycle

• Primary Source of Inoculum: Survives in plant debris, seed, and collateral hosts. Externally seed-borne.
• Host Range: Infects Sudan grass, Johnson grass, sorghum, wheat, barley, oats, sugarcane. Spores also associate with seeds of green gram, black gram, cowpea, and Teosinte.
• Secondary Spread: Through wind-borne conidia.

Favourable Conditions

• Temperature: 18 to 27°C is optimum for conidia germination.
• Moisture: Requires free water on the leaf surface for infection.
• Seasonality: Infection commonly occurs early in the wet season.

Management

1. Cultural Practices: Crop Rotation: To break the life cycle of the pathogen.
2. Resistant Varieties: DHM-1 is a resistant hybrid.
3. Seed Treatment: Captan or Thiram at 4 g/kg seed.
4. Chemical Control: Foliar Spray: Mancozeb @ 0.25%.

D) Charcoal Rot in Maize

Causal Agent: Macrophomina phaseolina
Sclerotial Stage: Rhizoctonia bataticola

Economic Importance

• Occurrence: Common in Rabi season, especially when post-flowering temperatures are high (35-45°C).
• Yield Losses: Ranges from 10-50%.

Symptoms

• Timing: Affects plants approaching maturity.
• Lesions on Roots: Initial brown, water-soaked lesions that later turn black.
• Stem Infection: Gray streaks develop on the surface of lower internodes. Leads to premature ripening, shredding, and breaking of the crown.
• Characteristic Symptom: When stalks are split open, numerous black sclerotia are observed on the vascular strands, giving the interior of stalks a charred appearance.Sclerotia may also be present on the roots.

Pathogen Characteristics

• Sclerotia: Round and black in color. Produced in large numbers.
• Pycnidia: Sometimes produced on stems or stalks.

Disease Cycle

• Host Range: Affects sorghum, bajra, ragi, and pulses.
• Survival: Can survive for over 16 years in infected plant debris.
• Primary Infection: Through soil-borne sclerotia.
• Secondary Spread: Irrigation water facilitates the spread of sclerotia.

Favourable Conditions

• Temperature and Weather: High temperatures (37°C) and dry weather during silking stage.
• Agronomic Practices: Imbalanced fertilizer application and high plant density increase disease severity.

Management

i) Cultural Practices

• • Long Crop Rotation: Use crops that are not hosts of the fungus.
  • Field Sanitation: Proper cleaning and disposal of infected debris.
  • Irrigation: Ensure adequate water supply from earhead emergence to maturity.

ii) Seed Treatment Carbendazim or Captan at 2 g/kg of seed.

iii) Resistant Varieties: DHM 103, DHM 105, Ganga Safed 2

E) Banded Leaf and Sheath Blight in Maize

Causal Agent: Rhizoctonia solani
Perfect Stage: Thanetophorus sasakii

Symptoms

• Discoloured Areas: Large, discoloured areas on leaves and sheaths with irregular dark bands.
• Blotching: Severe infection leads to blotching of leaf sheaths and leaves.
• Spread of Infection: Symptoms can extend to silk, glumes, and kernels under favorable conditions.
• Stage of Appearance: Generally appears at pre-flowering stage.
• Stalk and Internode Damage: Symptoms may also appear on the stalk, causing internodes to break at the point of infection.

Survival The fungus survives on weeds and in plant debris.

Management

1. Cultural Practices Clean Cultivation: Maintain a clean field to minimize fungal survival. Destruction of Crop Debris: Proper disposal of infected plant debris to reduce inoculum.
2. Chemical Control Spray Carbendazim or Propiconazole at 0.1% concentration.