Contents
Symptoms and Management of Smut of Onion
Causal organism: Urocystis magica (syn.= U. cepulae) and U. colchici.
Origin
Smut was first observed on the onion in the Connecticut river valley of USA in 1869.
Symptoms of Smut of Onion
1. The earliest symptom appears on cotyledons and young leaves as longitudinal blisters that are blackish with a silver sheen.
2. Dark pustules (sori) appear as slightly thickened areas at the base of seedlings near ground level. Blisters rupture to expose black, powdery spore masses (smut teliospores).
3. The seedling often dies before emergence. Large lesion can cause leaves to curve downward and usually are shed prematurely.
4. Infection progresses inward from leaf to leaf and infected leaf become stunted and may die within 3-4 weeks after emergence
5. If the plants survive, the disease become systemic and they remain at a vegetative stage for the entire growing season.
6. Elongated, raised black blisters can also be found in the outer scales of the developing bulb.
Favourable condition of Smut of Onion
▲ Optimum temperature for spore germination and growth are 13-22C. ▲ Infection of seedling can occur equally well at temperature of 12-25C. ▲ Above 29C, Onion seedling grow without infection in even heavily infested soil.
Control Measures/Management of Smut of Onion
♦ Prevent the movement of soil and plant debris among fields to prevent the smut pathogen from being introduced into other fields.
♦ Practice a threeyear or longer rotation to nonhosts such as small grains and corn.
♦ Transplants should be used instead of seed in infested soil.
♦ The disease can be controlled by seed treatment with Thiram @ 45 gm for 0.45 kg of seed.
♦ Spraying formaldehyde solution in the furrow.
