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Biological Control of Leaf Spot using a Fermented Food (Natto)

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I have 2 fig trees that are usually defoliated in late summer or early fall, around the time that the second crop starts to pop out. The second round of figs usually doesn't fully develop, they just fall off before getting large and edible. I knew that the leaves had some sort of disease (encouraged by the warm/humid Florida climate), so I did some searching, and found that figs are often affected by leaf blight caused by Cercospora fungi.

Then I came across this article that suggests that applying Bacillus subtilis can control Cercospora in sugar beets.


While the Bacillus subitilis bacteria might sound exotic and even scary to some people, I realized immediately that I have eaten it many times in the Japanese fermented food natto (aka 'sticky beans' aka 'stinky beans'

Natto is typically sold in the freezer section of Asian food stores, and costs about a dollar or two for a small portion (a few ounces). It can easily be thawed and run through a blender with some water to make a spray for foliage.

I plan on applying it in the afternoon/evening as direct sunlight might interfere. Might take several applications at weekly intervals to get the Bacillus-Fig interaction up to a point where the fungal disease is put into check.

This is all still theoretical. In the article I linked to, the researchers were 1) dealing with a different species of Cercospora, and 2) selecting for a strain of B. subtilis that is optimal (any random strain of the B. subtilis bacteria might or might not be good). But I think this is a natural approach that might help figs (and many other plants affected by Cercospora). This approach seems rather safe and low cost (and one can even make their own natto inexpensively using a small amount of store-bought natto as an inoculant).

There are many different species of Cercospora fungi that affect common edible and ornamental plants. A partial list of plants that are susceptible to Cercospora disease is provided below. Usually, the Cercospora disease is just called leaf spot or leaf blight, but for some plants, it has a more descriptive name:

sugarcane (black stripe)
cole crops - cabbage, broccoli, etc.
cannabis (olive leaf spot)
peppers (frog eye leaf spot)
watermelon and cucumber (cucurbit leaf spot)
strawberries leaf spot
many grasses
soybean (leaf blight, purple seed stain)
sugarcane (brown spot)
mango leaf spot
tobacco (frog eye leaf spot)
pearl millet
various drupe fruit trees (peach, plum, nectarine, etc)
soybean (frog eye leaf spot)
Corn (grey leaf spot)
Pelargonium and Geranium

My pear tree, persimmon tree, and mulberries also have brown spots on the leaves, so they will be fed natto as well.  It would be nice to establish a microbial ecology in the canopy that favors my permaculture plants over the fungal pests.
Brice Moss
Posts: 700
Location: rainier OR
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do let us know how it works I'll be watching with interest
Joel Hollingsworth
Posts: 2103
Location: Oakland, CA
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Here are some instructions on propagating the culture, which mention (in passing) that it's available in rice straw.


Sounds like a very inexpensive method, even if you had to make large vats of the stuff.
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Yes, according to legend, natto was discovered when a group of Samurai packed cooked soybeans in rice straw containers and went marching... they were hungry when they arrived, and they took a chance and ate the sticky fermented beans and lived to tell about it.
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