Rhizopus head rot

C/O: Rhizopus stolonifer

Symptoms:

• dark spots on the back of ripening heads, followed by a watery soft rot that later turns brown.
• As disease progresses, heads dry prematurely, shrivel, and tissues appear to shred.
• Inside shredded tissues, coarse, thread-like mycelial strands are observed, followed by the appearance of small black dots (sporangia).
• Sporangia are filled with spores that are easily released and wind-blown to other plants.
• Symptoms on the flower side of heads include the appearance of mycelium, a grayish, fuzzy substance that is covered with sporangia.

Etiology:

Pathogen produces dark brown or black coloured, non-septate hyphae.

The sporangiospores are dark coloured and ovoid.

Disease cycle:

• Saprophyte in nature
• Resting satge: zygospore
• Primary inoculum: zygospore, sporangiospore
• Secondary inoculum: wind borne conidia
• Transmission: air, water

Favorable condition:

• high temperatures and high relative humidity
• Prolonged rainy weather at flowering.
• Damage is caused by insects and caterpillars.

Management

• Treat the seeds with thiram or carbendazim at 2g/kg.
• Control the caterpillars feeding on the heads.
• Spray the head with Mancozeb at 2kg/ha during intermittent rainy season and repeat after 10 days, if the humid weather persists.