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Neem – your backyard source of insecticide

July 11, 2010

Neem, Azadirachta indica (Meliaceae), is a member of the mahogany family and is common in Thailand. Traditionally its bitter leaves have been used as a vermicide, killing intestinal worms. The leaves and flowers are commonly sold in Thai markets. Also, it has a reputation of being the source of a good insecticide. At Dokmai Garden we have tested that ability. We have noticed that some neem trees were defoliated by insects – do not use the leaves of such individuals! Different individuals contain different amounts of active compounds, which is why natural sources may vary considerably while commercial insecticides always have the same strength. Neem grows quickly, and you can prune it. We found that the recipe below was sufficient in killing aphids that attacked our Gardenia coronaria:

1. Collect 2 kg of fresh neem leaves.

2. Pour six litres of waters into a large bucket, crush the leaves and put them in the water. Put a stone on top to keep the leaves soaked.

3. Soak 12-16 hours.

4. Filter the brew using an old shirt.

5. Add a few drops of detergent if your aim is mealy bugs, and fill a plastic spray bottle with the filtrate. Spray your pests. Use all of the filtrate that same day – do not save it.

6. The aphids die within two days.

Since many plants have natural insecticides, we simply extract them and apply them to other plants. Melia (Melia azedarach, Meliaceae), rotenone (Derris elliptica, Fabaceae) and tobacco  (Nicotiana tabacum, Solanaceae) are other useful insecticidal plants. The good thing is that their insecticidal compounds are quickly degraded, and you save time and money by not going by car downtown to buy a commercial insecticide. 

The neem has bitter leaves, a red bark and grows into a handsome tree.

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