With the accent now on alternatives to fossil fuels, the large biomass of some weeds is being considered for future bio-fuels.
Insects, which pollinate crops, extensively use weeds as a source of nectar, when crops are not in flower. Predatory and parasitic insects also often feed on nectar from weeds. This assists in biological suppression of pests.
Many of the useful plants in Penny Woodward’s book (1) are considered weeds: she lists the particular uses of plants, whether they kill or repel, which insects a plant may repel, and the methods of use. Some of the plants listed are:
- insecticidal sprays: Lantana (Lantana camara), Camphor Laurel (Cinnamamom camphora), and Mustards (Brassica species)
- crushed fresh or dried leaves: Castor Oil Plant (Ricinus communis)
- insect repellent: Fennel (Foeniculum vulgare)
- nematode repellent: Mustards (Brassica species)
- anti-fungal and anti-bacterial; Stinging Nettle (Urtica dioica)
- excreted root chemicals help adjacent plants resist disease: Yarrow (Achillea millefolium)
Chandrasena (2) outlines a number of other uses:
- Weeds as raw materials for thatching, weaving and other products: A large variety of weeds, particularly grasses and sedges provide traditional material for roofing and thatching of for rural dwellings, and also as raw materials that can be woven into household products, such as baskets and mats.
- Weeds as raw materials for paper-making, bricks, and other industrial products: A large variety of colonising species, particularly grasses, are suitable for extraction of high quality lingo-cellulose fibre and other materials. The stems of Chromolaena odorata (Siam Weed) and Ageratum aadenophora
(Crofton Weed), which contain large amounts of cellulose, are also used for fibre-board manufacture in China. The large biomass produced by water hyacinth is also popular as raw material for paper and pulp industry in several countries in the Asia-Pacific region.
- weeds may be important sources of natural, plant-based dyes
- Some weeds provide useful ingredients of cosmetic products, such as soaps, perfumes, creams and hair oils.
- Woodward, Penny, 1997. Pest-repellent Plants. Hyland House, Victoria.
- Chandrasena, N, 2014. Living with weeds – a new paradigm. Indian Journal of Weed Science 46(1): 96–110, 2014 (PDF)