Disease of Sunflower

A) Sclerotinia Stem Rot

Symptoms:

• Symptoms appear during pod development.
• Leaves wilt, turn gray-green, then brown, curl, and die.
• Plants show a sickly appearance and eventually wither and die.
• White cottony mycelium and mustard seed-sized sclerotial bodies develop on the stem near the soil level.

Etiology:

• Causal Organism: Sclerotium rolfsii
• Sub-division: Deuteromycotina
• The fungus produces sclerotia, which are survival structures that persist in soil and plant debris.

Disease Cycle:

• Primary Infection: Occurs through sclerotia in soil and plant debris.
• Secondary Infection: Spread via sclerotia by contaminated implements and irrigation water.

Favourable Conditions: Alternating periods of high soil moisture and water stress.

Management:

• Collect and destroy plant debris.
• Seed treatment with Carboxin + Thiram at 0.3%.
• Use antagonistic fungi like Trichoderma harzianum.
• Spray Validamycin at 0.2% for control.

B) Alternaria Leaf Spot

Symptoms:

• Brown spots appear on leaves, stems, sepals, and petals.
• Lesions are dark brown to black, circular to oval, ranging from 0.2 to 0.5 mm in diameter.
• Spots are surrounded by chlorotic zones with necrotic centers.
• Under high humidity, spots enlarge with concentric rings, coalescing into bigger lesions, leading to drying and defoliation.
• The disease may cause rotting of flower heads, reducing seed quality and germination.

Etiology: Causal Organism: Alternaria helianthi

• Sub-division: Deuteromycotina
• The fungus produces conidia, which are spread through wind to infect plants.

Disease Cycle:

• Primary Infection: From infected seeds, host debris, and weed hosts.
• Secondary Infection: Mainly through windblown conidia.

Favourable Conditions: Rainy weather, cool winter climates, and late-sown crops increase susceptibility.

Management: Remove and destroy infected plant debris. Spray Mancozeb at 0.2% or Carbendazim at 0.1% two to three times at 10-day intervals, starting from the first appearance of the disease or 35 days after sowing (DAS).