Combatting Alternaria alternata
syn Alternaria tenuis

Alternaria alternata or tenuis is the species of Alternaria mold or fungus that causes leaf spot on many fruiting and ornamental plants. When it is present in the home, it causes asthma. Here's how to control it.

Leaf Spot on Fatsia Japonica
Leaf Spot on Fatsia Japonica
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Alternaria Leaf Spot

Alternaria leaf spot is a fungal disease affecting kale and other cole crops including ornamental cabbage.

Impatiens , geraniums and petunias may also be affected. A. alternata has also been identified as the culprit when Hibiscus, dahlia or vinca periwinkle plants have been infected.

There are also many other Alternaria species which infect hundreds of plants.

They all present pretty much the same symptoms:

Little brown spots will appear on the leaves. The spots range from the size of a pinhead to half an inch in diameter. The lesions may have concentric circles inside them and are usually surrounded by yellow circles.

A closely related disease called Alternaria brown spot is also caused by A. alternata. It affects citrus trees (both the fruit and leaves) causing shoot and leaf death. In severe infestations, it can cause fruit drop.

But this is not the only way in which this Alternaria mold species menaces the human race.

Alternaria Allergy

Alternaria tenuis allergies are fairly common.

According to the University of Wisconsin Department of Medicine, this is one of the molds most commonly associated with asthma. It not only affects the development of the disease, but its severity.

Researchers found that Alternaria alternata caused asthma symptoms independent of the presence of dust mites or other allergens.

Outdoors, the peak Alternaria allergy season is from summer to fall. The indoor levels of the fungus spores remains level throughout the year.

The research suggests that having your home cleaned frequently, and preventing moisture problems, will help to lower the indoor levels of Alternaria mold.

Alternaria Control in the Garden

The single best way to control Alternaria fungus on plants is to keep the leaves dry.

The spores are spread mainly by water and wind. They are harbored in soil and plant debris, so clean up any fallen leaves or clippings and remove them from the area. Don't compost them. Bag them.

Sometimes these measures alone will control the disease.

If not, spray disease prone plants with a copper fungicide every 3 weeks between spring and mid summer. You may need to reapply the fungicide more often during wet weather.

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