FloraQuest 2011: If We Cantelope, Lettuce Marry!

Neem Oil is a botanical extract used in agriculture as an organic pesticide and fungicide. The oil's active compound is a potassium salt of fatty acids. The oil is extracted from the seeds of the Neem Tree (Azadirachta indica), which is a semi-tropical tree native to the Indian sub-continent. A preparation of Neem oil can be either sprayed upon the plant's leaves or can be poured into the soil and absorbed by a plant's roots. Treated plants will absorb the active compound into its tissues and gain insecticidal and fungicidal properties. Exactly how these fatty acids in Neem Oil work is still a matter of speculation in the scientific community.

A common claim is that an insect which consumes the compound in Neem Oil will suffer a disruption to their reproductive and digestive systems on the hormonal level. I have read conflicting conclusions on this subject and will decline to reference them in favor of my own observations in using Neem Oil to combat Japanese Beetles on pole bean pants.

The Japanese Beetle (Popillia Japonica) is among the most destructive pests to ornamental, fruit and vegetable plants and turf grass to the eastern half of the continental United States and Canada. They are an invasive species which I began to see around 2002 or 2003 in my little corner of Chicagoland. That year the Virginia Creeper that grows on my deck trellis was completely skeletonized. The beetles also ate their share of wild Virginia Creeper and wild grape. They also damaged some corn in my garden they killed my Kentucky Wonder pole beans.

For a few years I resigned to the fate that I just could not grow things like beans and grapes anymore because of these loathsome little bugs.

In 2010 I read about Neem Oil and decided that I would employ the oil in an attempt to protect a substantial area of a vigorous pole bean called Fortex. With this wonder botanical and liberal planting of "super beans" I hoped that I would defeat the Japanese Beetle and enjoy tasty, meaty green beans once again!

I planted the beans in a 24' row along a 8' high trellis. The plants had grown tall and healthy by July and had set their first flowers by the time the first Japanese Beetles had hatched. I purchased a pre-mixed solution of a Neem Oil based insecticidal soap called K+Neem and began to spray the plants during the evening, after the pollinating bees retire and the insecticidal soap would pose no immediate threat to them. I repeated the application every week or sooner if there was a heavy rain. Within a few weeks the results were subtle but surprising!

As in years previous, my tall healthy plants soon were host to the Japanese Beetles. As before they started to cluster; eating the leaves and mounting each other. But instead of finding masses of leaves completely skeletonized, I found that the beetles would eat some of the leaves and then seem to loose their appetite. They just kind of hung about listlessly but flew about if disturbed. Found few beetles to be actually dead. Those that were had long turds hanging from them. Could Neem Oil give the beetles "Lethal Constipation!?"

I continued to apply the Neem Oil spray in the evenings about once a week throughout the summer. Hundreds of Japanese Beetles swarmed the plants but only ate enough of the leaves to become affected by the Neem Oil. For the first time in years, enjoyed green beans again. In fact I had over planted as I could not give away the quantities of green beans that I harvested. In contrast, the wild grapes growing in the vacant lot near my garden were thoroughly skeletonized as in years past, despite the fact that they were in the shade and the beans were in the full sun that the beetles prefer.

The final score card came in early this spring when I rototilled my garden. The claims that Neem Oil disrupts the Japanese Beetle's reproductive cycles seems to be substantiated: I hardly found any grubs in the soil.

This year, I will purchase a large volume of pure Neem Oil and mix my own solution of with the following recipe:

1 oz. of Neem oil
1 gallon water
A few drops of (non-insecticidal) dishwashing liquid to emulsify the oil

I will also broaden my use of Neem Oil as a fungicide this year. I have hope that this treatment will help with Early Blight in tomatoes and eggplants and Powdery Mildew in summer squash.

I also plan to spray the Neem Oil on cucumbers and melons in the hope that it might help inoculate cucumbers and melons from Bacterial Wilt which is spread by Cucumber Beetles, although I have yet to find a study to support this.

Footnote: See Japanese Beetle for a write-up on the life cycle, invasive history, and other common methods of control for The Japanese Beetle



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