Purple blotch is caused by by the fungus Alternaria porri. It is a concern throughout the entire growing season. Infection occurs when fungal spores from nearby plants are blown by wind into onion fields where they infect wounded plants. Overwinters in crop residue on or near the soil surface. Optimum temperatures for infection are between 77-85°F.

Symptoms of Purple Blotch of Onion and Garlic. 1. Symptoms first appear on leaves or seed stalks as small water-soaked lesions that quickly develop white centers. 2. Under favourable condition, these lesions enlarge, coalesce, become zonate and brown to purple that extend upward and downward. 3.

Downy mildew is identified by a purple-brown mold occurring in irregular shaped patches on onion leaves. The mold represents thousands of spores produced by the fungus in wet or humid weather. Severely affected leaves collapse and die in a few days.

Purple Blotch is caused by the fungus Alternaria porri. It is an important disease in warm, humid onion-growing regions around the world. Garlic and leeks may be affected as well as onions. Most long-day onion cultivars are susceptible, but sweet Spanish onions are generally more susceptible than common yellow cultivars. All short-day

Purple blotch of onion is caused by Alternaria porri. This fungus is also a pathogen of leek, garlic and chive, and is present throughout the United States and Canada. Field and storage loss estimates from this onion disease have ranged from 30 to …

Stemphylium leaf blight is more common than purple blotch in California, but symptoms and management are similar for both diseases. These fungi are often found infecting downy mildew lesions on onion but occur less commonly on garlic. Stemphlyium leaf blight is a common late-season problem in processing onions grown in the Tulelake area.

Purple Blotch is caused by the fungus Alternaria porri. It is an important disease in warm, humid onion-growing regions around the world. Garlic and leeks may be affected as well as onions. Most long-day onion cultivars are susceptible, but sweet Spanish onions are generally more susceptible than common yellow cultivars.

Purple blotch affects onions, garlic, leeks, and false shallot. The fungus that causes purple blotch (Alternaria porri) is closely related to the species that causes early blight on tomatoes and potatoes (Alternaria solani). Small, water-soaked, brownish lesions appear on leaves, flower stalks, and flowers of onions 1–4 days after infection occurs.

Nov 19, 2020 · Among the most commonly used fungicides, mancozeb, tebuconazole, difenaconazole and azoxystrobin were found to be the ideal for the management of purple blotch disease and increased garlic...

It is suspected that spores of the fungus that persist in the soil may directly infect the roots of young onion plants. These plants become systemically infected and serve as focal points for infection in commercial onion fields.