Purple blotch is a common fungal disease that affects onions, causing unsightly purple lesions on the outer layers of the bulb. This disease is caused by the fungus Alternaria porri and can result in reduced yields and poor quality onions.
Symptoms of purple blotch typically appear on the leaves first, appearing as small, purple spots that eventually grow in size and merge together. As the disease progresses, the spots may also appear on the bulbs themselves, leading to purple blotches forming on the outer layers.
Purple blotch thrives in warm, humid conditions, making it particularly problematic in areas with high humidity or frequent rainfall. The disease spreads through spores produced by the fungus, which can be carried by wind, water, or contaminated equipment.
To prevent purple blotch in onions, it is important to practice good crop rotation and sanitation practices. Avoid planting onions in the same location year after year, as this can allow the fungus to build up in the soil. Remove and destroy any infected plant material to prevent the spread of the disease.
Fungicides can also be used to control purple blotch, but it is important to start treatment early in the season before symptoms appear. Fungicides containing active ingredients such as mancozeb or azoxystrobin are effective against Alternaria porri and can help prevent the spread of the disease.
Overall, purple blotch can be a challenging disease to manage, but with proper prevention and control measures, it is possible to minimize its impact on onion crops. By practicing good sanitation, crop rotation, and utilizing fungicides when needed, growers can help protect their onions from the damaging effects of purple blotch.