Environmentally Friendly Biopesticide

Synthetic insecticide contains chemicals which have adverse effects on human health and the natural environment. The lush Chinese University campus has a great demand for insecticide. The Landscaping Section uses natural home-made pesticide which is both easy to make and environmentally friendly. It is Rotenone, an extract from the root of the plant Derris elliptica.

Belong to the Fabaceae (pea) family, the Derris elliptica is a large climber originating in India, Burma and Thailand and other tropical regions. It is also grown in Guangdong, Guangxi and Nanhai in China. The plants roots contain Rotenone which can be made into insecticidal formulations in the form of dust or aerosol.

The Landscaping Section buys dried Derris elliptica from an old-fashioned feed store in Yuen Long (photo 1). It is soaked in water for a day, then when soft, is pounded (photo 2) to loosen up the fibres. It is then returned to the water to soak for another three or four hours. The sap from the roots will turn the water into a milky-white fluid. This is then mixed with 50 or 100 parts water and sprayed on plants and grass.

Mr. Cheng Siu-bun of the Landscaping Section said, We generally spray Rotenone on campus once every three months. In pest-infested areas or during the mosquito breeding months of April and May, it may be shortened to once a month. Few people make insecticide this way now because the process is tedious and the plant is expensive. A can of synthetic insecticide may cost you a little over $10 but a catty of Derris elliptica costs over $40. However it is natural and safe for the human body. Well worth the trouble, I must say.