Gardening

What Causes White Rot On Alliums

Crops like garlic and onions are a favorite for many home gardeners. These kitchen staples are an excellent choice for overwintering in the vegetable patch and for growth in containers or raised beds. As with any crop, it’s important to pay close attention to the needs and growth requirements of the plants to ensure the best results possible.

This also means routine observation of potential pest and disease issues which may damage plants or diminish yields. One specific issue, allium white rot, should be monitored carefully, as it can result in complete loss of allium plants.

What is Sclerotium on Alliums?

Sclerotium on alliums, or allium white rot, is a fungal issue. What causes white rot specifically? Allium white rot is caused by a fungus called Sclerotium cepivorum. Even in small quantities, these fungal spores can quickly spread to infect large plantings of garlic and onions.

When conditions are ideal, with temperatures around 60 degrees F. (16 C.), the fungus is able to germinate and reproduce in the soil.

Allium white rot symptoms include yellowing of leaves and stunted plants. Upon closer inspection, growers of onions and garlic (and related allium plants) will find that the bulbs have also been affected. Bulbs of infected plants may appear dark in color and covered with a white, matted “fuzz” or black specks.

Treating Sclerotium White Rot

When allium white rot symptoms are first noticed in the garden, it is imperative that you promptly remove and destroy any infected plant matter. This will help to prevent the spread of the infection in the current season’s crop, though it may not prevent it completely.

Allium white rot can remain in the garden soil for up to 20 years after the initial infection. This makes it especially detrimental to home gardeners and those growing in limited spaces.

As with many soil-borne diseases, the best strategy is prevention. If allium plants have never been grown in the garden before, use plantings are disease free from the start. When buying, make certain only to purchase seed or transplants from a reputable source.

Once allium white rot has been established in your garden, controlling it may be difficult. Long-term crop rotation will be essential, as infected areas of the garden should no longer be used to grow onions or garlic. It will also be important to avoid the spread of the spores through the use of contaminated garden tools or even foot traffic on cultivated areas. 

Though the use of fungicides has provided some control, these options are seldom realistic for home gardeners. Select studies suggest that the use of solarization in the growing space has also helped to reduce the viability of the fungus present in the garden soil.

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