Purple Blotch On Onions Dealing With Purple Blotch In Onion Crops

Purple blotch in onion is caused by the fungus Alternaria porri. A fairly common disease of onions, it first manifests as small, water-soaked lesions that rapidly develop white centers. As the lesions progress, they turn from brown to purple with a halo of yellow.

What causes purple blotch in onions?
How do you control purple blotches in onions?
What is purple blotch?
How do you treat onion downy mildew?
Why do white onions turn red?
Are onions purple?
What causes purple splotches on skin?
How do you control a Stemphylium leaf blight of an onion?
What causes downy mildew in onions?
Which fungicide is best for onion?
What diseases affect onions?
Which fungicide is used against downy mildew?

What causes purple blotch in onions?

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 50 percent, and up to 100 percent in Colorado.

How do you control purple blotches in onions?

Most commercial onion crops must be protected from purple blotch by using repeated applications of protective fungicides. Solutions based on the fungicides boscalid, chlorothalonil, fenamidone and mancozeb (all @ 0.20 - 0.25%) can be sprayed preventively at fortnightly intervals starting one month after transplanting.

What is purple blotch?

Purple blotch, caused by the fungus Alternaria porri, is a commonly occurring foliar disease of onions in Michigan. It first appears as small, water-soaked lesions that quickly develop white centers. As they age, the lesions turn brown to purple, surrounded by a zone of yellow.

How do you treat onion downy mildew?

The only real way to eliminate downy mildew in onion plants is to spray them with a fungicide. Dithiocarbamate fungicides are used for downy mildew on onions. If you do get an infection that takes hold in your garden, try crop rotation.

Why do white onions turn red?

Red onions are full of pH sensitive cyoanthins. They turn pinker when exposed to bases and purple-blue when exposed to acids. Or maybe it's the other way around, but they do change color according to pH.

Are onions purple?

Red Onions – With their deep purple outer skin and reddish flesh, these are really the odd-guys out in the onion family. ... Red onions are most often used in salads, salsas, and other raw preparations for their color and relatively mild flavor.

What causes purple splotches on skin?

Purpura occurs when small blood vessels burst, causing blood to pool under the skin. This can create purple spots on the skin that range in size from small dots to large patches. Purpura spots are generally benign, but may indicate a more serious medical condition, such as a blood clotting disorder.

How do you control a Stemphylium leaf blight of an onion?

Solution of the active ingredients azoxystrobin + difenoconazole, boscalid + pyraclostrobin, chlorothalonil, iprodione, mancozeb and prochloraz are highly effective at reducing the growth in S. vesicarium. Treatments should be done when conditions are unfavorable for the fungus (cool and dry weather).

What causes downy mildew in onions?

Onion downy mildew is caused by the fungus-like (Oomycete) organism Peronospora destructor, which infects first the leaves and later bulbs of onions and shallots in mild, humid weather in late spring and summer. Some perennial onions such as chives may also be infected. It is worse in cool wet seasons and in wet areas.

Which fungicide is best for onion?

The latest evolution in the FarMore Technology platform is FarMore FI500 fungicide/insecticide, which offers direct-seeded onion growers early- season disease and insect protection for a healthy crop start.

What diseases affect onions?

Area and distribution Neck rot of onion, garlic and shallot is one of the major bulbs destroying diseases which are caused by Botrytis allii, B. squamosa and B. cinerea. The fungus usually infects mature plants through the neck tissues or through wounds in the bulbs.

Which fungicide is used against downy mildew?

Chlorothalonil and mancozeb are the main protectant fungicides for downy mildew. Copper is not as effective. Most fungicides labeled for downy mildew are also labeled for Phytophthora blight, which is caused by a related (oomycete) pathogen.