Disease of Sugarcane 

A) Red Rot 

Symptoms

• Tiny reddish lesions appear on the upper surface of leaves with dark dots in the center.
• Red spots on the mid-rib that develop into elongated lesions.
• Lesions are initially blood red with dark margins, later turning straw-colored in the center.
• Internal reddening of stalk tissues, especially in the vascular bundles.
• Cross-wise white patches interrupting the red tissues, giving a mosaic appearance.
• Acidic-sour odor emitted when infected canes are split open.
• Hollow, brittle cane stalks that break easily.
• Premature drying of leaves, giving a scorched appearance to the field.

Etiology

• Causal Organism: Colletotrichum falcatum
• Sub-division: Deuteromycotina
• Mode of Survival: Survives as mycelium and conidia in infected plant debris and setts.
• Mode of Spread: Primary Spread: Through infected setts used for planting. Secondary Spread: By conidia dispersed through irrigation water and cultivation tools.

Disease Cycle

• Primary Infection: Pathogen survives in infected setts and plant debris. Infection initiates from infected planting material.
• Secondary Infection: Airborne conidia spread through wind, water, and tools. Infection occurs through wounds or natural openings on the plant.

Favourable Conditions

• Mono-culturing of sugarcane and successive ratoon cropping.
• Waterlogged conditions and injuries caused by insects.
• High humidity and moderate temperatures favor disease development.

Management

• Cultural Practices:
  • Use disease-free setts from certified sources.
  • Crop rotation and avoid ratooning in infected fields.
  • Destroy infected plant debris to reduce inoculum.
• Chemical Control: Soak setts in 0.1% Carbendazim for 20 minutes before planting.
• Resistant Varieties: Plant resistant varieties like Co 419, Co 997, Co 1148, etc.

B) Smut of Sugarcane (Ustilago scitaminea)

Symptoms

• Central shoot is transformed into a long, whip-like black structure.
• Whip length varies from a few inches to several feet.
• Whip ruptures on maturity, releasing millions of black teliospores.
• Stunted growth and reduction in cane yield.
• Mummified arrows are seen:
  • Lower portion with normal flowers.
  • Upper portion with smutted whip.
• Affected clumps produce thin, lanky stalks with reduced sucrose content.

Etiology

• Causal Organism: Ustilago scitaminea
• Sub-division: Basidiomycotina
• Mode of Survival: Teliospores survive in soil and infected setts.
• Mode of Spread: Primary Spread: Through infected setts. Secondary Spread: Teliospores dispersed by wind and cultivation tools.

Disease Cycle

• Primary Infection: Infected setts are the primary source. Teliospores germinate and infect young buds.
• Secondary Infection: Airborne teliospores spread through wind. Infection occurs at the bud stage.

Favourable Conditions

• Mono-culturing of sugarcane and continuous ratooning.
• Dry weather during the tillering stage.
• Wounds on setts caused by insects or cultivation tools.

Management

• Cultural Practices:
  • Plant disease-free setts from smut-free fields.
  • Remove and destroy smutted clumps by burning.
  • Avoid ratooning of diseased crops.
• Physical Control: Hot water treatment of setts at 50°C for 2 hours.
• Chemical Control: Treat setts with 0.1% Carbendazim or 0.1% Carbathiin.
• Resistant Varieties: Grow resistant varieties like Co 419, Co 975, Co 1148, etc.

C) Wilt of Sugarcane (Cephalosporium sacchari)

Symptoms

• Visible at 4-5 months: The first symptoms appear in canes around 4-5 months of age.
• Withering in groups: Infected canes wither in clusters, showing a patchy appearance in the field.
• Stunted growth: Affected plants show stunted growth with yellowing and withering of crown leaves.
• Yellow midribs: Midribs of all leaves in the crown turn yellow, while the leaf lamina may remain green.
• Drying of leaves: The leaves dry up and become brittle.
• Hollowness in stem: Stems develop hollowness in the core or pith, which becomes brittle.
• Reddish discoloration: The pith shows reddish discoloration with longitudinal red streaks running from one internode to another.

Etiology

• Causal Organism: Cephalosporium sacchari
• Sub-division: Deuteromycotina
• Mode of Survival: Survives in infected setts and plant debris in the field.
• Mode of Spread: Primary Spread: Through infected setts. Secondary Spread: By wind, rain, and irrigation water.

Disease Cycle

• Primary Infection: Infected setts are the main source of primary infection.
• Secondary Infection: Airborne spores spread through wind, rain splashes, and irrigation water.
• Favourable Conditions: High day temperature (30-35°C) and low humidity (50-60%).
  • Low soil moisture, alkaline soils, and excess nitrogenous fertilizers.

Management

• Cultural Practices:
  • Select disease-free seed material from healthy plots.
  • Avoid ratooning in fields with a history of the disease.
  • Burn trash and stubbles to destroy residual inoculum.
• Physical Control: Hot water treatment of setts at 50°C for 2 hours.
• Chemical Control: Dipping setts in 0.05% Carbendazim for 15 minutes before planting.

D) Pokkah Boeng of Sugarcane (Fusarium moniliformae)

Symptoms

• Chlorotic Phase:
  • Chlorotic condition appears towards the base of young leaves, leading to:
    • Wrinkling, twisting, shortening, and malformation of leaves.
    • Irregular reddish stripes and specks on the chlorotic parts of mature leaves.
• Acute Phase (Top-Rot Phase):
  • Red specks and stripes develop on the young spindle.
  • Base of the young spindle becomes rotten and dries up quickly.
  • Top rot occurs in the tender apical tissue, leading to the death of the growing point.
• Knife Cut Phase:
  • Associated with the acute phase.
  • Transverse cuts appear on the rind of the stalk, resembling clean knife cuts.
  • Tissue removal gives a scarred knife-like appearance.

Etiology

• Causal Organism: Fusarium moniliformae
• Sub-division: Deuteromycotina
• Mode of Survival: Survives in infected plant debris and soil.
• Mode of Spread: Primary Spread: Through air-borne conidia dispersed by wind. Secondary Spread: Via infected setts, irrigation water, rain splashes, and soil.

Disease Cycle

• Primary Infection: Air-borne conidia infect young leaves and spindle.
• Secondary Infection: Spores spread through wind, rain, and irrigation water. Infected setts and soil also contribute to secondary spread.
• Favourable Conditions: Cool and dry conditions favor the survival of the fungus in plant debris.

Management

• Cultural Practices: Rogue out and destroy canes showing top rot or knife cut symptoms.
• Chemical Control: Spray 0.1% Carbendazim (1 gm/lit of water) or 0.2% Blitox-50 (2 gm/lit of water). Copper oxychloride or 0.3% Dithane M-45 (3 gm/lit of water) are effective fungicides.

E) Ratoon Stunt of Sugarcane

Symptoms:

• Stunted growth with reduced tillering and thin stalks.
• Shortened internodes and yellowish foliage (mild chlorosis).
• Discolored vascular bundles when mature canes are split open.
• Pink pin-head-like areas near the nodes in young canes.
• Decreased length, girth, and the number of canes per clump.

Etiology:

• Causal Organism: Clavibacter xyli pv. xyli (Xylem-limited fastidious bacteria).
• The bacteria colonize the xylem vessels, obstructing water and nutrient flow, leading to stunted growth.

Disease Cycle:

• Primary Infection: Occurs through the use of infected setts (seed cane).
• Secondary Infection: Spread by contaminated harvesting tools and equipment.
• Collateral Hosts: Maize, sorghum, Sudan grass, and Cynodon.

Management:

• Use disease-free setts for planting.
• Remove and burn infected clumps.
• Sterilize cutting knives and harvesting tools with antiseptic solutions.
• Hot Treatment Methods:
  • Hot air at 54°C for 8 hours.
  • Hot water at 50°C for 2 hours.
  • Aerated steam at 50°C for 1 hour.

F) Grassy Stunt of Sugarcane

Symptoms:

• Seen about two months after planting.
• Numerous lanky tillers are produced, giving a bushy or grass-like appearance.
• Pale yellow to completely chlorotic leaves that are thin and narrow.
• Reduction in internode length, leading to stunted growth.
• Infected clumps produce thin, weak, and small canes.
• Young leaves appear white (Albino), and buds are elongated, white, and papery.

Etiology:

• Causal Organism: Phytoplasma (a type of bacteria without a cell wall).
• The pathogen is transmitted through insect vectors, primarily aphids.

Disease Cycle:

• Primary Infection: Through collateral hosts, mainly sorghum.
• Secondary Infection: Spread by aphid vectors:
  • Aphis maidis
  • Rhopalosiphum maidis
  • Longiunguis sacchari

Management:

• Use disease-free setts for planting.
• Periodically remove and burn infected clumps.
• Avoid ratooning in affected areas to minimize disease spread.
• Hot Treatment Methods:
  • Hot Water Treatment (HWT) at 52°C for 30 minutes.
  • Aerated Steam Therapy (AST) at 50°C for 1 hour.
  • Steeping setts in Carbendazim (0.05%) solution for 15 minutes.
• Vector Control:
  • Spray Malathion or Dimethoate at 2 ml per liter to control aphid vectors.