Downey mildew

Downey mildew
    Causal organism: Peronospora arborescens (Berk.) de Bary.
    Symptoms
    • In India it is noticed during a middle of February,When the crop is fully grown.
    • It is also noticed during November-February.It appears on seedling and such affected seedling s are killed out right.
    • The leaves near the tips and margins are covered with pale brown spots.
    • On the under surface grey-violet fungal growth is seen.
    • Under favorable conditions the disease spreads and affected leaves dry up and become papery and brittle.
    • In severe cases of attack entire leaf is killed. Infection may spread to inflorescence and stem also. Yield loss from 7-65%.
    Etiology
    • Mycelia- Aseptate
    • Asexual spores – Barrel shape conidia borne on sporangiophore in asexual fruiting body sporangia
    • Sexual spore- Oospores borne in oogonium
    • Sporangiophores are erect and very long. They are 7-10 times dichotomously branched and the ultimate branches are fine, curved, sharp, diverging almost at right angles, pointed at the tip.
    • At the tip bears a single round –oval conidium .Sporangia are hyaline or pale violet.
    • Oospores are round yellow, thick walled surrounded by an irregularly thick and reddish brown wall
    Mode of survival
    • Primary source of inoculum: Oospores, affected debris.
    • Secondary source of inoculum: Zoospores spread through wind, water splash
    • The fungus infects Argemone mexicona, A. platyceras Meconosis sp. Papaver dubium, P. argimone and P. rhoeas.
    • The disease is carried from one season to another by means of thick walled oospores. It is not seed borne. Mycelia fragments on capsule may serve as source of infection
    Epidemiology
    • Temperature 22-240C
    • Relative humidity- 90-95 %
    • Intermittent rain fall
    • Susceptible host.
    Management
    • All disease plant should be uprooted, collected and destroyed.
    • Seed treatment with apron 35SD (metalaxyl) at 5g/kg +3 sprays of metalaxyl (ridomyl 25WP) 0.1 % at 20, 60 and 80days of sowing.
    • Foliar spraying with mancozeb 0.25 % also controls the disease.
    • The poppy line Vo.141 is found to be highly resistant to the disease.

Last modified: Thursday, 1 March 2012, 1:33 PM