Introduction

Onions are a vital crop in many agricultural economies, serving as a staple in kitchens worldwide due to their versatility and flavor. However, their cultivation is often challenged by various diseases that can severely impact yield and quality. Effective disease management is crucial to ensure a healthy crop and maximize productivity. In this blog, we will explore the most common diseases affecting onions, the symptoms to watch for, and the best practices for managing and preventing these issues. By implementing these strategies, farmers can protect their onion crops and achieve robust harvests season after season.

Basal Rot: Fusarium oxysporum f.sp. cepae

Symptoms:

The leaves turn yellow and then dry up slowly. The affected plant shows drying of leaf tip downwards. The entire plant shows complete drying of the foliage. The bulb of the affected plant shows soft rotting, and the roots get rotted. There will be a whitish mouldy growth on the scale. This disease can begin in the field and continue in storage. Pathogen The fungus produces many chlamydospores which are thick-walled resting spores and microconidia which are one celled and thin walled.

Management:

Growers must follow crop rotation and harvested bulbs must be thoroughly cured to reduce potential storage losses. Onions are very sensitive to low soil copper levels. To optimize crop production and disease susceptibility, additional soil copper fertility may be needed especially on mucky and sandy soils. Soil drenching with copper oxychloride 0.25 %.

Downy mildew: Peronospora destructor

Symptoms:

White downy growth appears on the surface of the leaves. Finally, the infected leaves are dried up. 128 Pathogen The sporangiophores are non-septate, long and swollen at the base. Sporangia are pyriform to fusiform, attached to the sterigmata by their pointed end. These sporangia germinate by one or two germ tubes. The coenocytic mycelium is intercellular with filamentous haustoria. Oogonia are formed in the intercellular spaces. As the upper portions of a leaf are killed, the fungus infects the next lower part of the leaf in each successive cycle of spore formation. Such cycles can be repeated several times until the leaf May 129 be completely killed. These repeated cycles of spore formation can result in severe and continued epidemics of DM if disease favourable environmental conditions persist.

Management:

Three spraying with Mancozeb 0.2 % is effective. Spraying should be started 20 days after transplanting and repeated at 10-12 days interval.

Summary

Onion crops can be susceptible to fungal diseases like Basal Rot and Downy Mildew. Basal Rot causes leaves to yellow and die progressively, leading to soft rot in the bulb. This fungus thrives in soil and survives on plant debris. To prevent this, rotate crops and ensure proper bulb curing after harvest. Additionally, sufficient soil copper levels are crucial. Downy Mildew, on the other hand, manifests as white patches on leaves followed by drying. Fungicide sprays with Mancozeb applied three times, starting 20 days after transplanting, can effectively control this disease.